diff --git a/lib/std/debug.zig b/lib/std/debug.zig
index 5ef25ec9fc..94f81908da 100644
--- a/lib/std/debug.zig
+++ b/lib/std/debug.zig
@@ -2428,7 +2428,7 @@ fn resetSegfaultHandler() void {
     os.sigaction(os.SIGILL, &act, null);
 }
 
-extern fn handleSegfaultLinux(sig: i32, info: *const os.siginfo_t, ctx_ptr: *const c_void) noreturn {
+fn handleSegfaultLinux(sig: i32, info: *const os.siginfo_t, ctx_ptr: *const c_void) callconv(.C) noreturn {
     // Reset to the default handler so that if a segfault happens in this handler it will crash
     // the process. Also when this handler returns, the original instruction will be repeated
     // and the resulting segfault will crash the process rather than continually dump stack traces.
diff --git a/lib/std/json/test.zig b/lib/std/json/test.zig
index 2dc5b860ed..5cc069bda3 100644
--- a/lib/std/json/test.zig
+++ b/lib/std/json/test.zig
@@ -22,7 +22,7 @@ fn err(comptime s: []const u8) void {
     const allocator = &std.heap.FixedBufferAllocator.init(&mem_buffer).allocator;
     var p = std.json.Parser.init(allocator, false);
 
-    if(p.parse(s)) |_| {
+    if (p.parse(s)) |_| {
         unreachable;
     } else |_| {}
 }
@@ -33,7 +33,7 @@ fn any(comptime s: []const u8) void {
     var mem_buffer: [1024 * 20]u8 = undefined;
     const allocator = &std.heap.FixedBufferAllocator.init(&mem_buffer).allocator;
     var p = std.json.Parser.init(allocator, false);
-    
+
     _ = p.parse(s) catch {};
 }
 
@@ -44,7 +44,7 @@ fn anyStreamingErrNonStreaming(comptime s: []const u8) void {
     const allocator = &std.heap.FixedBufferAllocator.init(&mem_buffer).allocator;
     var p = std.json.Parser.init(allocator, false);
 
-    if(p.parse(s)) |_| {
+    if (p.parse(s)) |_| {
         unreachable;
     } else |_| {}
 }
@@ -1742,9 +1742,9 @@ test "i_number_double_huge_neg_exp" {
 test "i_number_huge_exp" {
     return error.SkipZigTest;
     // FIXME Integer overflow in parseFloat
-//     any(
-//         \\[0.4e00669999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999969999999006]
-//     );
+    //     any(
+    //         \\[0.4e00669999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999969999999006]
+    //     );
 }
 
 test "i_number_neg_int_huge_exp" {
diff --git a/lib/std/math/sqrt.zig b/lib/std/math/sqrt.zig
index 493e2cacf6..800a7574ae 100644
--- a/lib/std/math/sqrt.zig
+++ b/lib/std/math/sqrt.zig
@@ -70,4 +70,3 @@ pub fn Sqrt(comptime T: type) type {
         else => T,
     };
 }
-
diff --git a/lib/std/mutex.zig b/lib/std/mutex.zig
index 94ec598a5c..7fbe4fde18 100644
--- a/lib/std/mutex.zig
+++ b/lib/std/mutex.zig
@@ -17,7 +17,7 @@ const ResetEvent = std.ResetEvent;
 /// Example usage:
 /// var m = Mutex.init();
 /// defer m.deinit();
-/// 
+///
 /// const lock = m.acquire();
 /// defer lock.release();
 /// ... critical code
diff --git a/lib/std/os/linux.zig b/lib/std/os/linux.zig
index efba40bb8d..94fad4cfb7 100644
--- a/lib/std/os/linux.zig
+++ b/lib/std/os/linux.zig
@@ -512,7 +512,7 @@ pub fn clock_gettime(clk_id: i32, tp: *timespec) usize {
     return syscall2(SYS_clock_gettime, @bitCast(usize, @as(isize, clk_id)), @ptrToInt(tp));
 }
 
-extern fn init_vdso_clock_gettime(clk: i32, ts: *timespec) usize {
+fn init_vdso_clock_gettime(clk: i32, ts: *timespec) callconv(.C) usize {
     const ptr = @intToPtr(?*const c_void, vdso.lookup(VDSO_CGT_VER, VDSO_CGT_SYM));
     // Note that we may not have a VDSO at all, update the stub address anyway
     // so that clock_gettime will fall back on the good old (and slow) syscall
diff --git a/lib/std/os/linux/arm-eabi.zig b/lib/std/os/linux/arm-eabi.zig
index 879805696c..2e55abd688 100644
--- a/lib/std/os/linux/arm-eabi.zig
+++ b/lib/std/os/linux/arm-eabi.zig
@@ -91,7 +91,7 @@ pub extern fn clone(func: extern fn (arg: usize) u8, stack: usize, flags: u32, a
 // LLVM calls this when the read-tp-hard feature is set to false. Currently, there is no way to pass
 // that to llvm via zig, see https://github.com/ziglang/zig/issues/2883.
 // LLVM expects libc to provide this function as __aeabi_read_tp, so it is exported if needed from special/c.zig.
-pub extern fn getThreadPointer() usize {
+pub fn getThreadPointer() callconv(.C) usize {
     return asm volatile ("mrc p15, 0, %[ret], c13, c0, 3"
         : [ret] "=r" (-> usize)
     );
diff --git a/lib/std/os/test.zig b/lib/std/os/test.zig
index 877b95af1f..1e51dd6f82 100644
--- a/lib/std/os/test.zig
+++ b/lib/std/os/test.zig
@@ -166,7 +166,7 @@ test "sigaltstack" {
 // analyzed
 const dl_phdr_info = if (@hasDecl(os, "dl_phdr_info")) os.dl_phdr_info else c_void;
 
-extern fn iter_fn(info: *dl_phdr_info, size: usize, data: ?*usize) i32 {
+fn iter_fn(info: *dl_phdr_info, size: usize, data: ?*usize) callconv(.C) i32 {
     if (builtin.os == .windows or builtin.os == .wasi or builtin.os == .macosx)
         return 0;
 
diff --git a/lib/std/special/c.zig b/lib/std/special/c.zig
index 1e63d9911f..604bfd277a 100644
--- a/lib/std/special/c.zig
+++ b/lib/std/special/c.zig
@@ -40,19 +40,19 @@ comptime {
 extern var _fltused: c_int = 1;
 
 extern fn main(argc: c_int, argv: [*:null]?[*:0]u8) c_int;
-extern fn wasm_start() void {
+fn wasm_start() callconv(.C) void {
     _ = main(0, undefined);
 }
 
-extern fn strcmp(s1: [*:0]const u8, s2: [*:0]const u8) c_int {
+fn strcmp(s1: [*:0]const u8, s2: [*:0]const u8) callconv(.C) c_int {
     return std.cstr.cmp(s1, s2);
 }
 
-extern fn strlen(s: [*:0]const u8) usize {
+fn strlen(s: [*:0]const u8) callconv(.C) usize {
     return std.mem.len(u8, s);
 }
 
-extern fn strncmp(_l: [*:0]const u8, _r: [*:0]const u8, _n: usize) c_int {
+fn strncmp(_l: [*:0]const u8, _r: [*:0]const u8, _n: usize) callconv(.C) c_int {
     if (_n == 0) return 0;
     var l = _l;
     var r = _r;
@@ -65,7 +65,7 @@ extern fn strncmp(_l: [*:0]const u8, _r: [*:0]const u8, _n: usize) c_int {
     return @as(c_int, l[0]) - @as(c_int, r[0]);
 }
 
-extern fn strerror(errnum: c_int) [*:0]const u8 {
+fn strerror(errnum: c_int) callconv(.C) [*:0]const u8 {
     return "TODO strerror implementation";
 }
 
@@ -188,7 +188,7 @@ comptime {
         @export("clone", clone, builtin.GlobalLinkage.Strong);
     }
 }
-extern fn __stack_chk_fail() noreturn {
+fn __stack_chk_fail() callconv(.C) noreturn {
     @panic("stack smashing detected");
 }
 
@@ -750,7 +750,6 @@ test "sqrt special" {
     std.testing.expect(std.math.isNan(sqrt(std.math.nan(f64))));
 }
 
-
 export fn sqrtf(x: f32) f32 {
     const tiny: f32 = 1.0e-30;
     const sign: i32 = @bitCast(i32, @as(u32, 0x80000000));
@@ -848,4 +847,3 @@ test "sqrtf special" {
     std.testing.expect(std.math.isNan(sqrtf(-1.0)));
     std.testing.expect(std.math.isNan(sqrtf(std.math.nan(f32))));
 }
-
diff --git a/lib/std/special/compiler_rt.zig b/lib/std/special/compiler_rt.zig
index f821918ccc..3a6e9c97e2 100644
--- a/lib/std/special/compiler_rt.zig
+++ b/lib/std/special/compiler_rt.zig
@@ -309,7 +309,7 @@ pub fn panic(msg: []const u8, error_return_trace: ?*builtin.StackTrace) noreturn
     }
 }
 
-extern fn __stack_chk_fail() noreturn {
+fn __stack_chk_fail() callconv(.C) noreturn {
     @panic("stack smashing detected");
 }
 
@@ -320,17 +320,17 @@ extern var __stack_chk_guard: usize = blk: {
     break :blk @bitCast(usize, buf);
 };
 
-extern fn __aeabi_unwind_cpp_pr0() void {
+fn __aeabi_unwind_cpp_pr0() callconv(.C) void {
     unreachable;
 }
-extern fn __aeabi_unwind_cpp_pr1() void {
+fn __aeabi_unwind_cpp_pr1() callconv(.C) void {
     unreachable;
 }
-extern fn __aeabi_unwind_cpp_pr2() void {
+fn __aeabi_unwind_cpp_pr2() callconv(.C) void {
     unreachable;
 }
 
-extern fn __divmoddi4(a: i64, b: i64, rem: *i64) i64 {
+fn __divmoddi4(a: i64, b: i64, rem: *i64) callconv(.C) i64 {
     @setRuntimeSafety(is_test);
 
     const d = __divdi3(a, b);
@@ -338,7 +338,7 @@ extern fn __divmoddi4(a: i64, b: i64, rem: *i64) i64 {
     return d;
 }
 
-extern fn __divdi3(a: i64, b: i64) i64 {
+fn __divdi3(a: i64, b: i64) callconv(.C) i64 {
     @setRuntimeSafety(is_test);
 
     // Set aside the sign of the quotient.
@@ -352,7 +352,7 @@ extern fn __divdi3(a: i64, b: i64) i64 {
     return @bitCast(i64, (res ^ sign) -% sign);
 }
 
-extern fn __moddi3(a: i64, b: i64) i64 {
+fn __moddi3(a: i64, b: i64) callconv(.C) i64 {
     @setRuntimeSafety(is_test);
 
     // Take absolute value of a and b via abs(x) = (x^(x >> 63)) - (x >> 63).
@@ -365,12 +365,12 @@ extern fn __moddi3(a: i64, b: i64) i64 {
     return (@bitCast(i64, r) ^ (a >> 63)) -% (a >> 63);
 }
 
-extern fn __udivdi3(a: u64, b: u64) u64 {
+fn __udivdi3(a: u64, b: u64) callconv(.C) u64 {
     @setRuntimeSafety(is_test);
     return __udivmoddi4(a, b, null);
 }
 
-extern fn __umoddi3(a: u64, b: u64) u64 {
+fn __umoddi3(a: u64, b: u64) callconv(.C) u64 {
     @setRuntimeSafety(is_test);
 
     var r: u64 = undefined;
@@ -378,7 +378,7 @@ extern fn __umoddi3(a: u64, b: u64) u64 {
     return r;
 }
 
-extern fn __aeabi_uidivmod(n: u32, d: u32) extern struct {
+fn __aeabi_uidivmod(n: u32, d: u32) callconv(.C) extern struct {
     q: u32,
     r: u32,
 } {
@@ -389,7 +389,7 @@ extern fn __aeabi_uidivmod(n: u32, d: u32) extern struct {
     return result;
 }
 
-extern fn __aeabi_uldivmod(n: u64, d: u64) extern struct {
+fn __aeabi_uldivmod(n: u64, d: u64) callconv(.C) extern struct {
     q: u64,
     r: u64,
 } {
@@ -400,7 +400,7 @@ extern fn __aeabi_uldivmod(n: u64, d: u64) extern struct {
     return result;
 }
 
-extern fn __aeabi_idivmod(n: i32, d: i32) extern struct {
+fn __aeabi_idivmod(n: i32, d: i32) callconv(.C) extern struct {
     q: i32,
     r: i32,
 } {
@@ -411,7 +411,7 @@ extern fn __aeabi_idivmod(n: i32, d: i32) extern struct {
     return result;
 }
 
-extern fn __aeabi_ldivmod(n: i64, d: i64) extern struct {
+fn __aeabi_ldivmod(n: i64, d: i64) callconv(.C) extern struct {
     q: i64,
     r: i64,
 } {
@@ -635,7 +635,7 @@ fn __aeabi_memcmp() callconv(.Naked) noreturn {
     unreachable;
 }
 
-extern fn __divmodsi4(a: i32, b: i32, rem: *i32) i32 {
+fn __divmodsi4(a: i32, b: i32, rem: *i32) callconv(.C) i32 {
     @setRuntimeSafety(is_test);
 
     const d = __divsi3(a, b);
@@ -643,7 +643,7 @@ extern fn __divmodsi4(a: i32, b: i32, rem: *i32) i32 {
     return d;
 }
 
-extern fn __udivmodsi4(a: u32, b: u32, rem: *u32) u32 {
+fn __udivmodsi4(a: u32, b: u32, rem: *u32) callconv(.C) u32 {
     @setRuntimeSafety(is_test);
 
     const d = __udivsi3(a, b);
@@ -651,7 +651,7 @@ extern fn __udivmodsi4(a: u32, b: u32, rem: *u32) u32 {
     return d;
 }
 
-extern fn __divsi3(n: i32, d: i32) i32 {
+fn __divsi3(n: i32, d: i32) callconv(.C) i32 {
     @setRuntimeSafety(is_test);
 
     // Set aside the sign of the quotient.
@@ -665,7 +665,7 @@ extern fn __divsi3(n: i32, d: i32) i32 {
     return @bitCast(i32, (res ^ sign) -% sign);
 }
 
-extern fn __udivsi3(n: u32, d: u32) u32 {
+fn __udivsi3(n: u32, d: u32) callconv(.C) u32 {
     @setRuntimeSafety(is_test);
 
     const n_uword_bits: c_uint = u32.bit_count;
@@ -706,13 +706,13 @@ extern fn __udivsi3(n: u32, d: u32) u32 {
     return q;
 }
 
-extern fn __modsi3(n: i32, d: i32) i32 {
+fn __modsi3(n: i32, d: i32) callconv(.C) i32 {
     @setRuntimeSafety(is_test);
 
     return n -% __divsi3(n, d) *% d;
 }
 
-extern fn __umodsi3(n: u32, d: u32) u32 {
+fn __umodsi3(n: u32, d: u32) callconv(.C) u32 {
     @setRuntimeSafety(is_test);
 
     return n -% __udivsi3(n, d) *% d;
diff --git a/lib/std/special/compiler_rt/addXf3.zig b/lib/std/special/compiler_rt/addXf3.zig
index e3dd1819c3..ac38e1c8cd 100644
--- a/lib/std/special/compiler_rt/addXf3.zig
+++ b/lib/std/special/compiler_rt/addXf3.zig
@@ -6,29 +6,29 @@ const std = @import("std");
 const builtin = @import("builtin");
 const compiler_rt = @import("../compiler_rt.zig");
 
-pub extern fn __addsf3(a: f32, b: f32) f32 {
+pub fn __addsf3(a: f32, b: f32) callconv(.C) f32 {
     return addXf3(f32, a, b);
 }
 
-pub extern fn __adddf3(a: f64, b: f64) f64 {
+pub fn __adddf3(a: f64, b: f64) callconv(.C) f64 {
     return addXf3(f64, a, b);
 }
 
-pub extern fn __addtf3(a: f128, b: f128) f128 {
+pub fn __addtf3(a: f128, b: f128) callconv(.C) f128 {
     return addXf3(f128, a, b);
 }
 
-pub extern fn __subsf3(a: f32, b: f32) f32 {
+pub fn __subsf3(a: f32, b: f32) callconv(.C) f32 {
     const neg_b = @bitCast(f32, @bitCast(u32, b) ^ (@as(u32, 1) << 31));
     return addXf3(f32, a, neg_b);
 }
 
-pub extern fn __subdf3(a: f64, b: f64) f64 {
+pub fn __subdf3(a: f64, b: f64) callconv(.C) f64 {
     const neg_b = @bitCast(f64, @bitCast(u64, b) ^ (@as(u64, 1) << 63));
     return addXf3(f64, a, neg_b);
 }
 
-pub extern fn __subtf3(a: f128, b: f128) f128 {
+pub fn __subtf3(a: f128, b: f128) callconv(.C) f128 {
     const neg_b = @bitCast(f128, @bitCast(u128, b) ^ (@as(u128, 1) << 127));
     return addXf3(f128, a, neg_b);
 }
diff --git a/lib/std/special/compiler_rt/ashlti3.zig b/lib/std/special/compiler_rt/ashlti3.zig
index 65b23f22e5..211515f9dd 100644
--- a/lib/std/special/compiler_rt/ashlti3.zig
+++ b/lib/std/special/compiler_rt/ashlti3.zig
@@ -1,7 +1,7 @@
 const builtin = @import("builtin");
 const compiler_rt = @import("../compiler_rt.zig");
 
-pub extern fn __ashlti3(a: i128, b: i32) i128 {
+pub fn __ashlti3(a: i128, b: i32) callconv(.C) i128 {
     var input = twords{ .all = a };
     var result: twords = undefined;
 
diff --git a/lib/std/special/compiler_rt/ashrti3.zig b/lib/std/special/compiler_rt/ashrti3.zig
index 40ee89c3c4..1bcd40d2e4 100644
--- a/lib/std/special/compiler_rt/ashrti3.zig
+++ b/lib/std/special/compiler_rt/ashrti3.zig
@@ -1,7 +1,7 @@
 const builtin = @import("builtin");
 const compiler_rt = @import("../compiler_rt.zig");
 
-pub extern fn __ashrti3(a: i128, b: i32) i128 {
+pub fn __ashrti3(a: i128, b: i32) callconv(.C) i128 {
     var input = twords{ .all = a };
     var result: twords = undefined;
 
diff --git a/lib/std/special/compiler_rt/aulldiv.zig b/lib/std/special/compiler_rt/aulldiv.zig
index afc96492c1..2e2dd364d5 100644
--- a/lib/std/special/compiler_rt/aulldiv.zig
+++ b/lib/std/special/compiler_rt/aulldiv.zig
@@ -1,6 +1,6 @@
 const builtin = @import("builtin");
 
-pub extern fn _alldiv(a: i64, b: i64) callconv(.Stdcall) i64 {
+pub fn _alldiv(a: i64, b: i64) callconv(.Stdcall) i64 {
     @setRuntimeSafety(builtin.is_test);
     const s_a = a >> (i64.bit_count - 1);
     const s_b = b >> (i64.bit_count - 1);
diff --git a/lib/std/special/compiler_rt/aullrem.zig b/lib/std/special/compiler_rt/aullrem.zig
index 748aaa0f89..4244f1bb80 100644
--- a/lib/std/special/compiler_rt/aullrem.zig
+++ b/lib/std/special/compiler_rt/aullrem.zig
@@ -1,6 +1,6 @@
 const builtin = @import("builtin");
 
-pub extern fn _allrem(a: i64, b: i64) callconv(.Stdcall) i64 {
+pub fn _allrem(a: i64, b: i64) callconv(.Stdcall) i64 {
     @setRuntimeSafety(builtin.is_test);
     const s_a = a >> (i64.bit_count - 1);
     const s_b = b >> (i64.bit_count - 1);
diff --git a/lib/std/special/compiler_rt/comparedf2.zig b/lib/std/special/compiler_rt/comparedf2.zig
index 95dc878630..b6e08c49f4 100644
--- a/lib/std/special/compiler_rt/comparedf2.zig
+++ b/lib/std/special/compiler_rt/comparedf2.zig
@@ -27,7 +27,7 @@ const LE_EQUAL = @as(c_int, 0);
 const LE_GREATER = @as(c_int, 1);
 const LE_UNORDERED = @as(c_int, 1);
 
-pub extern fn __ledf2(a: fp_t, b: fp_t) c_int {
+pub fn __ledf2(a: fp_t, b: fp_t) callconv(.C) c_int {
     @setRuntimeSafety(is_test);
     const aInt: srep_t = @bitCast(srep_t, a);
     const bInt: srep_t = @bitCast(srep_t, b);
@@ -70,7 +70,7 @@ const GE_EQUAL = @as(c_int, 0);
 const GE_GREATER = @as(c_int, 1);
 const GE_UNORDERED = @as(c_int, -1); // Note: different from LE_UNORDERED
 
-pub extern fn __gedf2(a: fp_t, b: fp_t) c_int {
+pub fn __gedf2(a: fp_t, b: fp_t) callconv(.C) c_int {
     @setRuntimeSafety(is_test);
     const aInt: srep_t = @bitCast(srep_t, a);
     const bInt: srep_t = @bitCast(srep_t, b);
@@ -94,26 +94,26 @@ pub extern fn __gedf2(a: fp_t, b: fp_t) c_int {
     }
 }
 
-pub extern fn __unorddf2(a: fp_t, b: fp_t) c_int {
+pub fn __unorddf2(a: fp_t, b: fp_t) callconv(.C) c_int {
     @setRuntimeSafety(is_test);
     const aAbs: rep_t = @bitCast(rep_t, a) & absMask;
     const bAbs: rep_t = @bitCast(rep_t, b) & absMask;
     return @boolToInt(aAbs > infRep or bAbs > infRep);
 }
 
-pub extern fn __eqdf2(a: fp_t, b: fp_t) c_int {
+pub fn __eqdf2(a: fp_t, b: fp_t) callconv(.C) c_int {
     return __ledf2(a, b);
 }
 
-pub extern fn __ltdf2(a: fp_t, b: fp_t) c_int {
+pub fn __ltdf2(a: fp_t, b: fp_t) callconv(.C) c_int {
     return __ledf2(a, b);
 }
 
-pub extern fn __nedf2(a: fp_t, b: fp_t) c_int {
+pub fn __nedf2(a: fp_t, b: fp_t) callconv(.C) c_int {
     return __ledf2(a, b);
 }
 
-pub extern fn __gtdf2(a: fp_t, b: fp_t) c_int {
+pub fn __gtdf2(a: fp_t, b: fp_t) callconv(.C) c_int {
     return __gedf2(a, b);
 }
 
diff --git a/lib/std/special/compiler_rt/comparesf2.zig b/lib/std/special/compiler_rt/comparesf2.zig
index 4468da4fbe..fdb5737ad3 100644
--- a/lib/std/special/compiler_rt/comparesf2.zig
+++ b/lib/std/special/compiler_rt/comparesf2.zig
@@ -27,7 +27,7 @@ const LE_EQUAL = @as(c_int, 0);
 const LE_GREATER = @as(c_int, 1);
 const LE_UNORDERED = @as(c_int, 1);
 
-pub extern fn __lesf2(a: fp_t, b: fp_t) c_int {
+pub fn __lesf2(a: fp_t, b: fp_t) callconv(.C) c_int {
     @setRuntimeSafety(is_test);
     const aInt: srep_t = @bitCast(srep_t, a);
     const bInt: srep_t = @bitCast(srep_t, b);
@@ -70,7 +70,7 @@ const GE_EQUAL = @as(c_int, 0);
 const GE_GREATER = @as(c_int, 1);
 const GE_UNORDERED = @as(c_int, -1); // Note: different from LE_UNORDERED
 
-pub extern fn __gesf2(a: fp_t, b: fp_t) c_int {
+pub fn __gesf2(a: fp_t, b: fp_t) callconv(.C) c_int {
     @setRuntimeSafety(is_test);
     const aInt: srep_t = @bitCast(srep_t, a);
     const bInt: srep_t = @bitCast(srep_t, b);
@@ -94,26 +94,26 @@ pub extern fn __gesf2(a: fp_t, b: fp_t) c_int {
     }
 }
 
-pub extern fn __unordsf2(a: fp_t, b: fp_t) c_int {
+pub fn __unordsf2(a: fp_t, b: fp_t) callconv(.C) c_int {
     @setRuntimeSafety(is_test);
     const aAbs: rep_t = @bitCast(rep_t, a) & absMask;
     const bAbs: rep_t = @bitCast(rep_t, b) & absMask;
     return @boolToInt(aAbs > infRep or bAbs > infRep);
 }
 
-pub extern fn __eqsf2(a: fp_t, b: fp_t) c_int {
+pub fn __eqsf2(a: fp_t, b: fp_t) callconv(.C) c_int {
     return __lesf2(a, b);
 }
 
-pub extern fn __ltsf2(a: fp_t, b: fp_t) c_int {
+pub fn __ltsf2(a: fp_t, b: fp_t) callconv(.C) c_int {
     return __lesf2(a, b);
 }
 
-pub extern fn __nesf2(a: fp_t, b: fp_t) c_int {
+pub fn __nesf2(a: fp_t, b: fp_t) callconv(.C) c_int {
     return __lesf2(a, b);
 }
 
-pub extern fn __gtsf2(a: fp_t, b: fp_t) c_int {
+pub fn __gtsf2(a: fp_t, b: fp_t) callconv(.C) c_int {
     return __gesf2(a, b);
 }
 
diff --git a/lib/std/special/compiler_rt/comparetf2.zig b/lib/std/special/compiler_rt/comparetf2.zig
index e973018455..f2969f2112 100644
--- a/lib/std/special/compiler_rt/comparetf2.zig
+++ b/lib/std/special/compiler_rt/comparetf2.zig
@@ -21,7 +21,7 @@ const infRep = exponentMask;
 const builtin = @import("builtin");
 const is_test = builtin.is_test;
 
-pub extern fn __letf2(a: f128, b: f128) c_int {
+pub fn __letf2(a: f128, b: f128) callconv(.C) c_int {
     @setRuntimeSafety(is_test);
 
     const aInt = @bitCast(rep_t, a);
@@ -65,7 +65,7 @@ const GE_EQUAL = @as(c_int, 0);
 const GE_GREATER = @as(c_int, 1);
 const GE_UNORDERED = @as(c_int, -1); // Note: different from LE_UNORDERED
 
-pub extern fn __getf2(a: f128, b: f128) c_int {
+pub fn __getf2(a: f128, b: f128) callconv(.C) c_int {
     @setRuntimeSafety(is_test);
 
     const aInt = @bitCast(srep_t, a);
@@ -90,7 +90,7 @@ pub extern fn __getf2(a: f128, b: f128) c_int {
         GE_GREATER;
 }
 
-pub extern fn __unordtf2(a: f128, b: f128) c_int {
+pub fn __unordtf2(a: f128, b: f128) callconv(.C) c_int {
     @setRuntimeSafety(is_test);
 
     const aAbs = @bitCast(rep_t, a) & absMask;
diff --git a/lib/std/special/compiler_rt/divdf3.zig b/lib/std/special/compiler_rt/divdf3.zig
index 9937b09497..a8afd4a3a6 100644
--- a/lib/std/special/compiler_rt/divdf3.zig
+++ b/lib/std/special/compiler_rt/divdf3.zig
@@ -5,7 +5,7 @@
 const std = @import("std");
 const builtin = @import("builtin");
 
-pub extern fn __divdf3(a: f64, b: f64) f64 {
+pub fn __divdf3(a: f64, b: f64) callconv(.C) f64 {
     @setRuntimeSafety(builtin.is_test);
     const Z = @IntType(false, f64.bit_count);
     const SignedZ = @IntType(true, f64.bit_count);
diff --git a/lib/std/special/compiler_rt/divsf3.zig b/lib/std/special/compiler_rt/divsf3.zig
index 4ee2eed36c..ea882b4927 100644
--- a/lib/std/special/compiler_rt/divsf3.zig
+++ b/lib/std/special/compiler_rt/divsf3.zig
@@ -5,7 +5,7 @@
 const std = @import("std");
 const builtin = @import("builtin");
 
-pub extern fn __divsf3(a: f32, b: f32) f32 {
+pub fn __divsf3(a: f32, b: f32) callconv(.C) f32 {
     @setRuntimeSafety(builtin.is_test);
     const Z = @IntType(false, f32.bit_count);
 
diff --git a/lib/std/special/compiler_rt/divti3.zig b/lib/std/special/compiler_rt/divti3.zig
index fcb23a50d9..2b878f5269 100644
--- a/lib/std/special/compiler_rt/divti3.zig
+++ b/lib/std/special/compiler_rt/divti3.zig
@@ -1,7 +1,7 @@
 const udivmod = @import("udivmod.zig").udivmod;
 const builtin = @import("builtin");
 
-pub extern fn __divti3(a: i128, b: i128) i128 {
+pub fn __divti3(a: i128, b: i128) callconv(.C) i128 {
     @setRuntimeSafety(builtin.is_test);
 
     const s_a = a >> (i128.bit_count - 1);
@@ -16,7 +16,7 @@ pub extern fn __divti3(a: i128, b: i128) i128 {
 }
 
 const v128 = @Vector(2, u64);
-pub extern fn __divti3_windows_x86_64(a: v128, b: v128) v128 {
+pub fn __divti3_windows_x86_64(a: v128, b: v128) callconv(.C) v128 {
     return @bitCast(v128, @call(.{ .modifier = .always_inline }, __divti3, .{
         @bitCast(i128, a),
         @bitCast(i128, b),
diff --git a/lib/std/special/compiler_rt/extendXfYf2.zig b/lib/std/special/compiler_rt/extendXfYf2.zig
index 427bd4ec24..10227043aa 100644
--- a/lib/std/special/compiler_rt/extendXfYf2.zig
+++ b/lib/std/special/compiler_rt/extendXfYf2.zig
@@ -2,19 +2,19 @@ const std = @import("std");
 const builtin = @import("builtin");
 const is_test = builtin.is_test;
 
-pub extern fn __extendsfdf2(a: f32) f64 {
+pub fn __extendsfdf2(a: f32) callconv(.C) f64 {
     return @call(.{ .modifier = .always_inline }, extendXfYf2, .{ f64, f32, @bitCast(u32, a) });
 }
 
-pub extern fn __extenddftf2(a: f64) f128 {
+pub fn __extenddftf2(a: f64) callconv(.C) f128 {
     return @call(.{ .modifier = .always_inline }, extendXfYf2, .{ f128, f64, @bitCast(u64, a) });
 }
 
-pub extern fn __extendsftf2(a: f32) f128 {
+pub fn __extendsftf2(a: f32) callconv(.C) f128 {
     return @call(.{ .modifier = .always_inline }, extendXfYf2, .{ f128, f32, @bitCast(u32, a) });
 }
 
-pub extern fn __extendhfsf2(a: u16) f32 {
+pub fn __extendhfsf2(a: u16) callconv(.C) f32 {
     return @call(.{ .modifier = .always_inline }, extendXfYf2, .{ f32, f16, a });
 }
 
diff --git a/lib/std/special/compiler_rt/fixdfdi.zig b/lib/std/special/compiler_rt/fixdfdi.zig
index c108fd15aa..fb3b31d6e8 100644
--- a/lib/std/special/compiler_rt/fixdfdi.zig
+++ b/lib/std/special/compiler_rt/fixdfdi.zig
@@ -1,7 +1,7 @@
 const fixint = @import("fixint.zig").fixint;
 const builtin = @import("builtin");
 
-pub extern fn __fixdfdi(a: f64) i64 {
+pub fn __fixdfdi(a: f64) callconv(.C) i64 {
     @setRuntimeSafety(builtin.is_test);
     return fixint(f64, i64, a);
 }
diff --git a/lib/std/special/compiler_rt/fixdfsi.zig b/lib/std/special/compiler_rt/fixdfsi.zig
index 83a17b2b0d..de21c86e43 100644
--- a/lib/std/special/compiler_rt/fixdfsi.zig
+++ b/lib/std/special/compiler_rt/fixdfsi.zig
@@ -1,7 +1,7 @@
 const fixint = @import("fixint.zig").fixint;
 const builtin = @import("builtin");
 
-pub extern fn __fixdfsi(a: f64) i32 {
+pub fn __fixdfsi(a: f64) callconv(.C) i32 {
     @setRuntimeSafety(builtin.is_test);
     return fixint(f64, i32, a);
 }
diff --git a/lib/std/special/compiler_rt/fixdfti.zig b/lib/std/special/compiler_rt/fixdfti.zig
index e30f885cf6..0e21f0ba19 100644
--- a/lib/std/special/compiler_rt/fixdfti.zig
+++ b/lib/std/special/compiler_rt/fixdfti.zig
@@ -1,7 +1,7 @@
 const fixint = @import("fixint.zig").fixint;
 const builtin = @import("builtin");
 
-pub extern fn __fixdfti(a: f64) i128 {
+pub fn __fixdfti(a: f64) callconv(.C) i128 {
     @setRuntimeSafety(builtin.is_test);
     return fixint(f64, i128, a);
 }
diff --git a/lib/std/special/compiler_rt/fixsfdi.zig b/lib/std/special/compiler_rt/fixsfdi.zig
index ffa81d13ab..d3aaf9d470 100644
--- a/lib/std/special/compiler_rt/fixsfdi.zig
+++ b/lib/std/special/compiler_rt/fixsfdi.zig
@@ -1,7 +1,7 @@
 const fixint = @import("fixint.zig").fixint;
 const builtin = @import("builtin");
 
-pub extern fn __fixsfdi(a: f32) i64 {
+pub fn __fixsfdi(a: f32) callconv(.C) i64 {
     @setRuntimeSafety(builtin.is_test);
     return fixint(f32, i64, a);
 }
diff --git a/lib/std/special/compiler_rt/fixsfsi.zig b/lib/std/special/compiler_rt/fixsfsi.zig
index 9a94b4395b..81aa01dfa1 100644
--- a/lib/std/special/compiler_rt/fixsfsi.zig
+++ b/lib/std/special/compiler_rt/fixsfsi.zig
@@ -1,7 +1,7 @@
 const fixint = @import("fixint.zig").fixint;
 const builtin = @import("builtin");
 
-pub extern fn __fixsfsi(a: f32) i32 {
+pub fn __fixsfsi(a: f32) callconv(.C) i32 {
     @setRuntimeSafety(builtin.is_test);
     return fixint(f32, i32, a);
 }
diff --git a/lib/std/special/compiler_rt/fixsfti.zig b/lib/std/special/compiler_rt/fixsfti.zig
index 806a1678aa..d7ce4b3a60 100644
--- a/lib/std/special/compiler_rt/fixsfti.zig
+++ b/lib/std/special/compiler_rt/fixsfti.zig
@@ -1,7 +1,7 @@
 const fixint = @import("fixint.zig").fixint;
 const builtin = @import("builtin");
 
-pub extern fn __fixsfti(a: f32) i128 {
+pub fn __fixsfti(a: f32) callconv(.C) i128 {
     @setRuntimeSafety(builtin.is_test);
     return fixint(f32, i128, a);
 }
diff --git a/lib/std/special/compiler_rt/fixtfdi.zig b/lib/std/special/compiler_rt/fixtfdi.zig
index 8d99231b74..0ef3aa2259 100644
--- a/lib/std/special/compiler_rt/fixtfdi.zig
+++ b/lib/std/special/compiler_rt/fixtfdi.zig
@@ -1,7 +1,7 @@
 const fixint = @import("fixint.zig").fixint;
 const builtin = @import("builtin");
 
-pub extern fn __fixtfdi(a: f128) i64 {
+pub fn __fixtfdi(a: f128) callconv(.C) i64 {
     @setRuntimeSafety(builtin.is_test);
     return fixint(f128, i64, a);
 }
diff --git a/lib/std/special/compiler_rt/fixtfsi.zig b/lib/std/special/compiler_rt/fixtfsi.zig
index f3f83634b2..15e89a11b0 100644
--- a/lib/std/special/compiler_rt/fixtfsi.zig
+++ b/lib/std/special/compiler_rt/fixtfsi.zig
@@ -1,7 +1,7 @@
 const fixint = @import("fixint.zig").fixint;
 const builtin = @import("builtin");
 
-pub extern fn __fixtfsi(a: f128) i32 {
+pub fn __fixtfsi(a: f128) callconv(.C) i32 {
     @setRuntimeSafety(builtin.is_test);
     return fixint(f128, i32, a);
 }
diff --git a/lib/std/special/compiler_rt/fixtfti.zig b/lib/std/special/compiler_rt/fixtfti.zig
index 07d38f2c3b..733fa1eed1 100644
--- a/lib/std/special/compiler_rt/fixtfti.zig
+++ b/lib/std/special/compiler_rt/fixtfti.zig
@@ -1,7 +1,7 @@
 const fixint = @import("fixint.zig").fixint;
 const builtin = @import("builtin");
 
-pub extern fn __fixtfti(a: f128) i128 {
+pub fn __fixtfti(a: f128) callconv(.C) i128 {
     @setRuntimeSafety(builtin.is_test);
     return fixint(f128, i128, a);
 }
diff --git a/lib/std/special/compiler_rt/fixunsdfdi.zig b/lib/std/special/compiler_rt/fixunsdfdi.zig
index 1fa7ed758e..9d41d4b740 100644
--- a/lib/std/special/compiler_rt/fixunsdfdi.zig
+++ b/lib/std/special/compiler_rt/fixunsdfdi.zig
@@ -1,7 +1,7 @@
 const fixuint = @import("fixuint.zig").fixuint;
 const builtin = @import("builtin");
 
-pub extern fn __fixunsdfdi(a: f64) u64 {
+pub fn __fixunsdfdi(a: f64) callconv(.C) u64 {
     @setRuntimeSafety(builtin.is_test);
     return fixuint(f64, u64, a);
 }
diff --git a/lib/std/special/compiler_rt/fixunsdfsi.zig b/lib/std/special/compiler_rt/fixunsdfsi.zig
index a77cb8df89..044523512c 100644
--- a/lib/std/special/compiler_rt/fixunsdfsi.zig
+++ b/lib/std/special/compiler_rt/fixunsdfsi.zig
@@ -1,7 +1,7 @@
 const fixuint = @import("fixuint.zig").fixuint;
 const builtin = @import("builtin");
 
-pub extern fn __fixunsdfsi(a: f64) u32 {
+pub fn __fixunsdfsi(a: f64) callconv(.C) u32 {
     @setRuntimeSafety(builtin.is_test);
     return fixuint(f64, u32, a);
 }
diff --git a/lib/std/special/compiler_rt/fixunsdfti.zig b/lib/std/special/compiler_rt/fixunsdfti.zig
index 6e1ded46e5..3dcec6bf89 100644
--- a/lib/std/special/compiler_rt/fixunsdfti.zig
+++ b/lib/std/special/compiler_rt/fixunsdfti.zig
@@ -1,7 +1,7 @@
 const fixuint = @import("fixuint.zig").fixuint;
 const builtin = @import("builtin");
 
-pub extern fn __fixunsdfti(a: f64) u128 {
+pub fn __fixunsdfti(a: f64) callconv(.C) u128 {
     @setRuntimeSafety(builtin.is_test);
     return fixuint(f64, u128, a);
 }
diff --git a/lib/std/special/compiler_rt/fixunssfdi.zig b/lib/std/special/compiler_rt/fixunssfdi.zig
index 36d4acc28c..a42121aeec 100644
--- a/lib/std/special/compiler_rt/fixunssfdi.zig
+++ b/lib/std/special/compiler_rt/fixunssfdi.zig
@@ -1,7 +1,7 @@
 const fixuint = @import("fixuint.zig").fixuint;
 const builtin = @import("builtin");
 
-pub extern fn __fixunssfdi(a: f32) u64 {
+pub fn __fixunssfdi(a: f32) callconv(.C) u64 {
     @setRuntimeSafety(builtin.is_test);
     return fixuint(f32, u64, a);
 }
diff --git a/lib/std/special/compiler_rt/fixunssfsi.zig b/lib/std/special/compiler_rt/fixunssfsi.zig
index 53130286a1..00f7c8ad22 100644
--- a/lib/std/special/compiler_rt/fixunssfsi.zig
+++ b/lib/std/special/compiler_rt/fixunssfsi.zig
@@ -1,7 +1,7 @@
 const fixuint = @import("fixuint.zig").fixuint;
 const builtin = @import("builtin");
 
-pub extern fn __fixunssfsi(a: f32) u32 {
+pub fn __fixunssfsi(a: f32) callconv(.C) u32 {
     @setRuntimeSafety(builtin.is_test);
     return fixuint(f32, u32, a);
 }
diff --git a/lib/std/special/compiler_rt/fixunssfti.zig b/lib/std/special/compiler_rt/fixunssfti.zig
index f0cd788d2e..dff9eb7498 100644
--- a/lib/std/special/compiler_rt/fixunssfti.zig
+++ b/lib/std/special/compiler_rt/fixunssfti.zig
@@ -1,7 +1,7 @@
 const fixuint = @import("fixuint.zig").fixuint;
 const builtin = @import("builtin");
 
-pub extern fn __fixunssfti(a: f32) u128 {
+pub fn __fixunssfti(a: f32) callconv(.C) u128 {
     @setRuntimeSafety(builtin.is_test);
     return fixuint(f32, u128, a);
 }
diff --git a/lib/std/special/compiler_rt/fixunstfdi.zig b/lib/std/special/compiler_rt/fixunstfdi.zig
index e352044708..907116c165 100644
--- a/lib/std/special/compiler_rt/fixunstfdi.zig
+++ b/lib/std/special/compiler_rt/fixunstfdi.zig
@@ -1,7 +1,7 @@
 const fixuint = @import("fixuint.zig").fixuint;
 const builtin = @import("builtin");
 
-pub extern fn __fixunstfdi(a: f128) u64 {
+pub fn __fixunstfdi(a: f128) callconv(.C) u64 {
     @setRuntimeSafety(builtin.is_test);
     return fixuint(f128, u64, a);
 }
diff --git a/lib/std/special/compiler_rt/fixunstfsi.zig b/lib/std/special/compiler_rt/fixunstfsi.zig
index 579c559790..c66a3f18b4 100644
--- a/lib/std/special/compiler_rt/fixunstfsi.zig
+++ b/lib/std/special/compiler_rt/fixunstfsi.zig
@@ -1,7 +1,7 @@
 const fixuint = @import("fixuint.zig").fixuint;
 const builtin = @import("builtin");
 
-pub extern fn __fixunstfsi(a: f128) u32 {
+pub fn __fixunstfsi(a: f128) callconv(.C) u32 {
     @setRuntimeSafety(builtin.is_test);
     return fixuint(f128, u32, a);
 }
diff --git a/lib/std/special/compiler_rt/fixunstfti.zig b/lib/std/special/compiler_rt/fixunstfti.zig
index cd6178164a..1867c69234 100644
--- a/lib/std/special/compiler_rt/fixunstfti.zig
+++ b/lib/std/special/compiler_rt/fixunstfti.zig
@@ -1,7 +1,7 @@
 const fixuint = @import("fixuint.zig").fixuint;
 const builtin = @import("builtin");
 
-pub extern fn __fixunstfti(a: f128) u128 {
+pub fn __fixunstfti(a: f128) callconv(.C) u128 {
     @setRuntimeSafety(builtin.is_test);
     return fixuint(f128, u128, a);
 }
diff --git a/lib/std/special/compiler_rt/floatdidf.zig b/lib/std/special/compiler_rt/floatdidf.zig
index 1610136413..93bd0c8a3e 100644
--- a/lib/std/special/compiler_rt/floatdidf.zig
+++ b/lib/std/special/compiler_rt/floatdidf.zig
@@ -4,7 +4,7 @@ const std = @import("std");
 const twop52: f64 = 0x1.0p52;
 const twop32: f64 = 0x1.0p32;
 
-pub extern fn __floatdidf(a: i64) f64 {
+pub fn __floatdidf(a: i64) callconv(.C) f64 {
     @setRuntimeSafety(builtin.is_test);
 
     if (a == 0) return 0;
diff --git a/lib/std/special/compiler_rt/floatsiXf.zig b/lib/std/special/compiler_rt/floatsiXf.zig
index 917dfb47fc..30a09de90c 100644
--- a/lib/std/special/compiler_rt/floatsiXf.zig
+++ b/lib/std/special/compiler_rt/floatsiXf.zig
@@ -53,17 +53,17 @@ fn floatsiXf(comptime T: type, a: i32) T {
     return @bitCast(T, result);
 }
 
-pub extern fn __floatsisf(arg: i32) f32 {
+pub fn __floatsisf(arg: i32) callconv(.C) f32 {
     @setRuntimeSafety(builtin.is_test);
     return @call(.{ .modifier = .always_inline }, floatsiXf, .{ f32, arg });
 }
 
-pub extern fn __floatsidf(arg: i32) f64 {
+pub fn __floatsidf(arg: i32) callconv(.C) f64 {
     @setRuntimeSafety(builtin.is_test);
     return @call(.{ .modifier = .always_inline }, floatsiXf, .{ f64, arg });
 }
 
-pub extern fn __floatsitf(arg: i32) f128 {
+pub fn __floatsitf(arg: i32) callconv(.C) f128 {
     @setRuntimeSafety(builtin.is_test);
     return @call(.{ .modifier = .always_inline }, floatsiXf, .{ f128, arg });
 }
diff --git a/lib/std/special/compiler_rt/floattidf.zig b/lib/std/special/compiler_rt/floattidf.zig
index 1e83674598..6b5013287b 100644
--- a/lib/std/special/compiler_rt/floattidf.zig
+++ b/lib/std/special/compiler_rt/floattidf.zig
@@ -5,7 +5,7 @@ const maxInt = std.math.maxInt;
 
 const DBL_MANT_DIG = 53;
 
-pub extern fn __floattidf(arg: i128) f64 {
+pub fn __floattidf(arg: i128) callconv(.C) f64 {
     @setRuntimeSafety(is_test);
 
     if (arg == 0)
diff --git a/lib/std/special/compiler_rt/floattisf.zig b/lib/std/special/compiler_rt/floattisf.zig
index 0c02bfff1f..3f020dadd8 100644
--- a/lib/std/special/compiler_rt/floattisf.zig
+++ b/lib/std/special/compiler_rt/floattisf.zig
@@ -5,7 +5,7 @@ const maxInt = std.math.maxInt;
 
 const FLT_MANT_DIG = 24;
 
-pub extern fn __floattisf(arg: i128) f32 {
+pub fn __floattisf(arg: i128) callconv(.C) f32 {
     @setRuntimeSafety(is_test);
 
     if (arg == 0)
diff --git a/lib/std/special/compiler_rt/floattitf.zig b/lib/std/special/compiler_rt/floattitf.zig
index aac22e36d0..90bc241306 100644
--- a/lib/std/special/compiler_rt/floattitf.zig
+++ b/lib/std/special/compiler_rt/floattitf.zig
@@ -5,7 +5,7 @@ const maxInt = std.math.maxInt;
 
 const LDBL_MANT_DIG = 113;
 
-pub extern fn __floattitf(arg: i128) f128 {
+pub fn __floattitf(arg: i128) callconv(.C) f128 {
     @setRuntimeSafety(is_test);
 
     if (arg == 0)
diff --git a/lib/std/special/compiler_rt/floatundidf.zig b/lib/std/special/compiler_rt/floatundidf.zig
index 68759a2acd..c8803b4c6c 100644
--- a/lib/std/special/compiler_rt/floatundidf.zig
+++ b/lib/std/special/compiler_rt/floatundidf.zig
@@ -5,7 +5,7 @@ const twop52: f64 = 0x1.0p52;
 const twop84: f64 = 0x1.0p84;
 const twop84_plus_twop52: f64 = 0x1.00000001p84;
 
-pub extern fn __floatundidf(a: u64) f64 {
+pub fn __floatundidf(a: u64) callconv(.C) f64 {
     @setRuntimeSafety(builtin.is_test);
 
     if (a == 0) return 0;
diff --git a/lib/std/special/compiler_rt/floatunditf.zig b/lib/std/special/compiler_rt/floatunditf.zig
index 9af83a2b5d..b574d21bd8 100644
--- a/lib/std/special/compiler_rt/floatunditf.zig
+++ b/lib/std/special/compiler_rt/floatunditf.zig
@@ -2,7 +2,7 @@ const builtin = @import("builtin");
 const is_test = builtin.is_test;
 const std = @import("std");
 
-pub extern fn __floatunditf(a: u128) f128 {
+pub fn __floatunditf(a: u128) callconv(.C) f128 {
     @setRuntimeSafety(is_test);
 
     if (a == 0) {
diff --git a/lib/std/special/compiler_rt/floatunsidf.zig b/lib/std/special/compiler_rt/floatunsidf.zig
index d744009aea..92a7870806 100644
--- a/lib/std/special/compiler_rt/floatunsidf.zig
+++ b/lib/std/special/compiler_rt/floatunsidf.zig
@@ -4,7 +4,7 @@ const maxInt = std.math.maxInt;
 
 const implicitBit = @as(u64, 1) << 52;
 
-pub extern fn __floatunsidf(arg: u32) f64 {
+pub fn __floatunsidf(arg: u32) callconv(.C) f64 {
     @setRuntimeSafety(builtin.is_test);
 
     if (arg == 0) return 0.0;
diff --git a/lib/std/special/compiler_rt/floatunsitf.zig b/lib/std/special/compiler_rt/floatunsitf.zig
index 18397f8ad0..a10ff6b703 100644
--- a/lib/std/special/compiler_rt/floatunsitf.zig
+++ b/lib/std/special/compiler_rt/floatunsitf.zig
@@ -2,7 +2,7 @@ const builtin = @import("builtin");
 const is_test = builtin.is_test;
 const std = @import("std");
 
-pub extern fn __floatunsitf(a: u64) f128 {
+pub fn __floatunsitf(a: u64) callconv(.C) f128 {
     @setRuntimeSafety(is_test);
 
     if (a == 0) {
diff --git a/lib/std/special/compiler_rt/floatuntidf.zig b/lib/std/special/compiler_rt/floatuntidf.zig
index 5d3a201058..5b5adc0491 100644
--- a/lib/std/special/compiler_rt/floatuntidf.zig
+++ b/lib/std/special/compiler_rt/floatuntidf.zig
@@ -5,7 +5,7 @@ const maxInt = std.math.maxInt;
 
 const DBL_MANT_DIG = 53;
 
-pub extern fn __floatuntidf(arg: u128) f64 {
+pub fn __floatuntidf(arg: u128) callconv(.C) f64 {
     @setRuntimeSafety(is_test);
 
     if (arg == 0)
diff --git a/lib/std/special/compiler_rt/floatuntisf.zig b/lib/std/special/compiler_rt/floatuntisf.zig
index e450ad9a48..33e6e41a84 100644
--- a/lib/std/special/compiler_rt/floatuntisf.zig
+++ b/lib/std/special/compiler_rt/floatuntisf.zig
@@ -5,7 +5,7 @@ const maxInt = std.math.maxInt;
 
 const FLT_MANT_DIG = 24;
 
-pub extern fn __floatuntisf(arg: u128) f32 {
+pub fn __floatuntisf(arg: u128) callconv(.C) f32 {
     @setRuntimeSafety(is_test);
 
     if (arg == 0)
diff --git a/lib/std/special/compiler_rt/floatuntitf.zig b/lib/std/special/compiler_rt/floatuntitf.zig
index f92942e034..0b96076206 100644
--- a/lib/std/special/compiler_rt/floatuntitf.zig
+++ b/lib/std/special/compiler_rt/floatuntitf.zig
@@ -5,7 +5,7 @@ const maxInt = std.math.maxInt;
 
 const LDBL_MANT_DIG = 113;
 
-pub extern fn __floatuntitf(arg: u128) f128 {
+pub fn __floatuntitf(arg: u128) callconv(.C) f128 {
     @setRuntimeSafety(is_test);
 
     if (arg == 0)
diff --git a/lib/std/special/compiler_rt/lshrti3.zig b/lib/std/special/compiler_rt/lshrti3.zig
index 329968ae40..043be5e2a2 100644
--- a/lib/std/special/compiler_rt/lshrti3.zig
+++ b/lib/std/special/compiler_rt/lshrti3.zig
@@ -1,7 +1,7 @@
 const builtin = @import("builtin");
 const compiler_rt = @import("../compiler_rt.zig");
 
-pub extern fn __lshrti3(a: i128, b: i32) i128 {
+pub fn __lshrti3(a: i128, b: i32) callconv(.C) i128 {
     var input = twords{ .all = a };
     var result: twords = undefined;
 
diff --git a/lib/std/special/compiler_rt/modti3.zig b/lib/std/special/compiler_rt/modti3.zig
index d983ecba5f..a9d1f48468 100644
--- a/lib/std/special/compiler_rt/modti3.zig
+++ b/lib/std/special/compiler_rt/modti3.zig
@@ -6,7 +6,7 @@ const udivmod = @import("udivmod.zig").udivmod;
 const builtin = @import("builtin");
 const compiler_rt = @import("../compiler_rt.zig");
 
-pub extern fn __modti3(a: i128, b: i128) i128 {
+pub fn __modti3(a: i128, b: i128) callconv(.C) i128 {
     @setRuntimeSafety(builtin.is_test);
 
     const s_a = a >> (i128.bit_count - 1); // s = a < 0 ? -1 : 0
@@ -21,7 +21,7 @@ pub extern fn __modti3(a: i128, b: i128) i128 {
 }
 
 const v128 = @Vector(2, u64);
-pub extern fn __modti3_windows_x86_64(a: v128, b: v128) v128 {
+pub fn __modti3_windows_x86_64(a: v128, b: v128) callconv(.C) v128 {
     return @bitCast(v128, @call(.{ .modifier = .always_inline }, __modti3, .{
         @bitCast(i128, a),
         @bitCast(i128, b),
diff --git a/lib/std/special/compiler_rt/mulXf3.zig b/lib/std/special/compiler_rt/mulXf3.zig
index 11ee0b49a4..9457bfb86e 100644
--- a/lib/std/special/compiler_rt/mulXf3.zig
+++ b/lib/std/special/compiler_rt/mulXf3.zig
@@ -6,13 +6,13 @@ const std = @import("std");
 const builtin = @import("builtin");
 const compiler_rt = @import("../compiler_rt.zig");
 
-pub extern fn __multf3(a: f128, b: f128) f128 {
+pub fn __multf3(a: f128, b: f128) callconv(.C) f128 {
     return mulXf3(f128, a, b);
 }
-pub extern fn __muldf3(a: f64, b: f64) f64 {
+pub fn __muldf3(a: f64, b: f64) callconv(.C) f64 {
     return mulXf3(f64, a, b);
 }
-pub extern fn __mulsf3(a: f32, b: f32) f32 {
+pub fn __mulsf3(a: f32, b: f32) callconv(.C) f32 {
     return mulXf3(f32, a, b);
 }
 
diff --git a/lib/std/special/compiler_rt/muldi3.zig b/lib/std/special/compiler_rt/muldi3.zig
index 3efc5a9ac6..4f605d441c 100644
--- a/lib/std/special/compiler_rt/muldi3.zig
+++ b/lib/std/special/compiler_rt/muldi3.zig
@@ -39,7 +39,7 @@ fn __muldsi3(a: u32, b: u32) i64 {
     return r.all;
 }
 
-pub extern fn __muldi3(a: i64, b: i64) i64 {
+pub fn __muldi3(a: i64, b: i64) callconv(.C) i64 {
     @setRuntimeSafety(builtin.is_test);
 
     const x = dwords{ .all = a };
diff --git a/lib/std/special/compiler_rt/mulodi4.zig b/lib/std/special/compiler_rt/mulodi4.zig
index 21c7fd1f97..b70d1657e7 100644
--- a/lib/std/special/compiler_rt/mulodi4.zig
+++ b/lib/std/special/compiler_rt/mulodi4.zig
@@ -3,7 +3,7 @@ const compiler_rt = @import("../compiler_rt.zig");
 const maxInt = std.math.maxInt;
 const minInt = std.math.minInt;
 
-pub extern fn __mulodi4(a: i64, b: i64, overflow: *c_int) i64 {
+pub fn __mulodi4(a: i64, b: i64, overflow: *c_int) callconv(.C) i64 {
     @setRuntimeSafety(builtin.is_test);
 
     const min = @bitCast(i64, @as(u64, 1 << (i64.bit_count - 1)));
diff --git a/lib/std/special/compiler_rt/muloti4.zig b/lib/std/special/compiler_rt/muloti4.zig
index ad6ad43808..190959b801 100644
--- a/lib/std/special/compiler_rt/muloti4.zig
+++ b/lib/std/special/compiler_rt/muloti4.zig
@@ -1,7 +1,7 @@
 const builtin = @import("builtin");
 const compiler_rt = @import("../compiler_rt.zig");
 
-pub extern fn __muloti4(a: i128, b: i128, overflow: *c_int) i128 {
+pub fn __muloti4(a: i128, b: i128, overflow: *c_int) callconv(.C) i128 {
     @setRuntimeSafety(builtin.is_test);
 
     const min = @bitCast(i128, @as(u128, 1 << (i128.bit_count - 1)));
diff --git a/lib/std/special/compiler_rt/multi3.zig b/lib/std/special/compiler_rt/multi3.zig
index 56ff56cbb2..f46bd55421 100644
--- a/lib/std/special/compiler_rt/multi3.zig
+++ b/lib/std/special/compiler_rt/multi3.zig
@@ -5,7 +5,7 @@ const compiler_rt = @import("../compiler_rt.zig");
 // ae684fad6d34858c014c94da69c15e7774a633c3
 // 2018-08-13
 
-pub extern fn __multi3(a: i128, b: i128) i128 {
+pub fn __multi3(a: i128, b: i128) callconv(.C) i128 {
     @setRuntimeSafety(builtin.is_test);
     const x = twords{ .all = a };
     const y = twords{ .all = b };
@@ -15,7 +15,7 @@ pub extern fn __multi3(a: i128, b: i128) i128 {
 }
 
 const v128 = @Vector(2, u64);
-pub extern fn __multi3_windows_x86_64(a: v128, b: v128) v128 {
+pub fn __multi3_windows_x86_64(a: v128, b: v128) callconv(.C) v128 {
     return @bitCast(v128, @call(.{ .modifier = .always_inline }, __multi3, .{
         @bitCast(i128, a),
         @bitCast(i128, b),
diff --git a/lib/std/special/compiler_rt/negXf2.zig b/lib/std/special/compiler_rt/negXf2.zig
index c4be085d62..e21e36b955 100644
--- a/lib/std/special/compiler_rt/negXf2.zig
+++ b/lib/std/special/compiler_rt/negXf2.zig
@@ -1,10 +1,10 @@
 const std = @import("std");
 
-pub extern fn __negsf2(a: f32) f32 {
+pub fn __negsf2(a: f32) callconv(.C) f32 {
     return negXf2(f32, a);
 }
 
-pub extern fn __negdf2(a: f64) f64 {
+pub fn __negdf2(a: f64) callconv(.C) f64 {
     return negXf2(f64, a);
 }
 
diff --git a/lib/std/special/compiler_rt/popcountdi2.zig b/lib/std/special/compiler_rt/popcountdi2.zig
index ea36b0ec44..b7e7220c7b 100644
--- a/lib/std/special/compiler_rt/popcountdi2.zig
+++ b/lib/std/special/compiler_rt/popcountdi2.zig
@@ -2,7 +2,7 @@ const builtin = @import("builtin");
 const compiler_rt = @import("../compiler_rt.zig");
 
 // ported from llvm compiler-rt 8.0.0rc3 95e1c294cb0415a377a7b1d6c7c7d4f89e1c04e4
-pub extern fn __popcountdi2(a: i64) i32 {
+pub fn __popcountdi2(a: i64) callconv(.C) i32 {
     var x2 = @bitCast(u64, a);
     x2 = x2 - ((x2 >> 1) & 0x5555555555555555);
     // Every 2 bits holds the sum of every pair of bits (32)
diff --git a/lib/std/special/compiler_rt/truncXfYf2.zig b/lib/std/special/compiler_rt/truncXfYf2.zig
index d231c0d416..10b097e777 100644
--- a/lib/std/special/compiler_rt/truncXfYf2.zig
+++ b/lib/std/special/compiler_rt/truncXfYf2.zig
@@ -1,22 +1,22 @@
 const std = @import("std");
 
-pub extern fn __truncsfhf2(a: f32) u16 {
+pub fn __truncsfhf2(a: f32) callconv(.C) u16 {
     return @bitCast(u16, truncXfYf2(f16, f32, a));
 }
 
-pub extern fn __truncdfhf2(a: f64) u16 {
+pub fn __truncdfhf2(a: f64) callconv(.C) u16 {
     return @bitCast(u16, truncXfYf2(f16, f64, a));
 }
 
-pub extern fn __trunctfsf2(a: f128) f32 {
+pub fn __trunctfsf2(a: f128) callconv(.C) f32 {
     return truncXfYf2(f32, f128, a);
 }
 
-pub extern fn __trunctfdf2(a: f128) f64 {
+pub fn __trunctfdf2(a: f128) callconv(.C) f64 {
     return truncXfYf2(f64, f128, a);
 }
 
-pub extern fn __truncdfsf2(a: f64) f32 {
+pub fn __truncdfsf2(a: f64) callconv(.C) f32 {
     return truncXfYf2(f32, f64, a);
 }
 
diff --git a/lib/std/special/compiler_rt/udivmoddi4.zig b/lib/std/special/compiler_rt/udivmoddi4.zig
index de86c845e5..79f0f39986 100644
--- a/lib/std/special/compiler_rt/udivmoddi4.zig
+++ b/lib/std/special/compiler_rt/udivmoddi4.zig
@@ -1,7 +1,7 @@
 const udivmod = @import("udivmod.zig").udivmod;
 const builtin = @import("builtin");
 
-pub extern fn __udivmoddi4(a: u64, b: u64, maybe_rem: ?*u64) u64 {
+pub fn __udivmoddi4(a: u64, b: u64, maybe_rem: ?*u64) callconv(.C) u64 {
     @setRuntimeSafety(builtin.is_test);
     return udivmod(u64, a, b, maybe_rem);
 }
diff --git a/lib/std/special/compiler_rt/udivmodti4.zig b/lib/std/special/compiler_rt/udivmodti4.zig
index c74dff512d..7a3405c3e2 100644
--- a/lib/std/special/compiler_rt/udivmodti4.zig
+++ b/lib/std/special/compiler_rt/udivmodti4.zig
@@ -2,13 +2,13 @@ const udivmod = @import("udivmod.zig").udivmod;
 const builtin = @import("builtin");
 const compiler_rt = @import("../compiler_rt.zig");
 
-pub extern fn __udivmodti4(a: u128, b: u128, maybe_rem: ?*u128) u128 {
+pub fn __udivmodti4(a: u128, b: u128, maybe_rem: ?*u128) callconv(.C) u128 {
     @setRuntimeSafety(builtin.is_test);
     return udivmod(u128, a, b, maybe_rem);
 }
 
 const v128 = @Vector(2, u64);
-pub extern fn __udivmodti4_windows_x86_64(a: v128, b: v128, maybe_rem: ?*u128) v128 {
+pub fn __udivmodti4_windows_x86_64(a: v128, b: v128, maybe_rem: ?*u128) callconv(.C) v128 {
     @setRuntimeSafety(builtin.is_test);
     return @bitCast(v128, udivmod(u128, @bitCast(u128, a), @bitCast(u128, b), maybe_rem));
 }
diff --git a/lib/std/special/compiler_rt/udivti3.zig b/lib/std/special/compiler_rt/udivti3.zig
index ab451859bf..6283285e01 100644
--- a/lib/std/special/compiler_rt/udivti3.zig
+++ b/lib/std/special/compiler_rt/udivti3.zig
@@ -1,13 +1,13 @@
 const udivmodti4 = @import("udivmodti4.zig");
 const builtin = @import("builtin");
 
-pub extern fn __udivti3(a: u128, b: u128) u128 {
+pub fn __udivti3(a: u128, b: u128) callconv(.C) u128 {
     @setRuntimeSafety(builtin.is_test);
     return udivmodti4.__udivmodti4(a, b, null);
 }
 
 const v128 = @Vector(2, u64);
-pub extern fn __udivti3_windows_x86_64(a: v128, b: v128) v128 {
+pub fn __udivti3_windows_x86_64(a: v128, b: v128) callconv(.C) v128 {
     @setRuntimeSafety(builtin.is_test);
     return udivmodti4.__udivmodti4_windows_x86_64(a, b, null);
 }
diff --git a/lib/std/special/compiler_rt/umodti3.zig b/lib/std/special/compiler_rt/umodti3.zig
index 9d4a42147c..4f9890f512 100644
--- a/lib/std/special/compiler_rt/umodti3.zig
+++ b/lib/std/special/compiler_rt/umodti3.zig
@@ -2,7 +2,7 @@ const udivmodti4 = @import("udivmodti4.zig");
 const builtin = @import("builtin");
 const compiler_rt = @import("../compiler_rt.zig");
 
-pub extern fn __umodti3(a: u128, b: u128) u128 {
+pub fn __umodti3(a: u128, b: u128) callconv(.C) u128 {
     @setRuntimeSafety(builtin.is_test);
     var r: u128 = undefined;
     _ = udivmodti4.__udivmodti4(a, b, &r);
@@ -10,7 +10,7 @@ pub extern fn __umodti3(a: u128, b: u128) u128 {
 }
 
 const v128 = @Vector(2, u64);
-pub extern fn __umodti3_windows_x86_64(a: v128, b: v128) v128 {
+pub fn __umodti3_windows_x86_64(a: v128, b: v128) callconv(.C) v128 {
     return @bitCast(v128, @call(.{ .modifier = .always_inline }, __umodti3, .{
         @bitCast(u128, a),
         @bitCast(u128, b),
diff --git a/lib/std/start.zig b/lib/std/start.zig
index a919107266..7c1353e18b 100644
--- a/lib/std/start.zig
+++ b/lib/std/start.zig
@@ -43,11 +43,7 @@ comptime {
     }
 }
 
-fn _DllMainCRTStartup(
-    hinstDLL: std.os.windows.HINSTANCE,
-    fdwReason: std.os.windows.DWORD,
-    lpReserved: std.os.windows.LPVOID,
-) callconv(.Stdcall) std.os.windows.BOOL {
+fn _DllMainCRTStartup(hinstDLL: std.os.windows.HINSTANCE, fdwReason: std.os.windows.DWORD, lpReserved: std.os.windows.LPVOID) callconv(.Stdcall) std.os.windows.BOOL {
     if (@hasDecl(root, "DllMain")) {
         return root.DllMain(hinstDLL, fdwReason, lpReserved);
     }
@@ -55,13 +51,13 @@ fn _DllMainCRTStartup(
     return std.os.windows.TRUE;
 }
 
-extern fn wasm_freestanding_start() void {
+fn wasm_freestanding_start() callconv(.C) void {
     // This is marked inline because for some reason LLVM in release mode fails to inline it,
     // and we want fewer call frames in stack traces.
     _ = @call(.{ .modifier = .always_inline }, callMain, .{});
 }
 
-extern fn EfiMain(handle: uefi.Handle, system_table: *uefi.tables.SystemTable) usize {
+fn EfiMain(handle: uefi.Handle, system_table: *uefi.tables.SystemTable) callconv(.C) usize {
     const bad_efi_main_ret = "expected return type of main to be 'void', 'noreturn', or 'usize'";
     uefi.handle = handle;
     uefi.system_table = system_table;
@@ -198,7 +194,7 @@ fn callMainWithArgs(argc: usize, argv: [*][*:0]u8, envp: [][*:0]u8) u8 {
     return initEventLoopAndCallMain();
 }
 
-extern fn main(c_argc: i32, c_argv: [*][*:0]u8, c_envp: [*:null]?[*:0]u8) i32 {
+fn main(c_argc: i32, c_argv: [*][*:0]u8, c_envp: [*:null]?[*:0]u8) callconv(.C) i32 {
     var env_count: usize = 0;
     while (c_envp[env_count] != null) : (env_count += 1) {}
     const envp = @ptrCast([*][*:0]u8, c_envp)[0..env_count];
diff --git a/lib/std/thread.zig b/lib/std/thread.zig
index dcc762f30e..c482405c44 100644
--- a/lib/std/thread.zig
+++ b/lib/std/thread.zig
@@ -156,7 +156,7 @@ pub const Thread = struct {
                     thread: Thread,
                     inner: Context,
                 };
-                extern fn threadMain(raw_arg: windows.LPVOID) windows.DWORD {
+                fn threadMain(raw_arg: windows.LPVOID) callconv(.C) windows.DWORD {
                     const arg = if (@sizeOf(Context) == 0) {} else @ptrCast(*Context, @alignCast(@alignOf(Context), raw_arg)).*;
                     switch (@typeId(@TypeOf(startFn).ReturnType)) {
                         .Int => {
@@ -198,7 +198,7 @@ pub const Thread = struct {
         }
 
         const MainFuncs = struct {
-            extern fn linuxThreadMain(ctx_addr: usize) u8 {
+            fn linuxThreadMain(ctx_addr: usize) callconv(.C) u8 {
                 const arg = if (@sizeOf(Context) == 0) {} else @intToPtr(*const Context, ctx_addr).*;
 
                 switch (@typeId(@TypeOf(startFn).ReturnType)) {
@@ -212,7 +212,7 @@ pub const Thread = struct {
                     else => @compileError("expected return type of startFn to be 'u8', 'noreturn', 'void', or '!void'"),
                 }
             }
-            extern fn posixThreadMain(ctx: ?*c_void) ?*c_void {
+            fn posixThreadMain(ctx: ?*c_void) callconv(.C) ?*c_void {
                 if (@sizeOf(Context) == 0) {
                     _ = startFn({});
                     return null;
diff --git a/lib/std/unicode/throughput_test.zig b/lib/std/unicode/throughput_test.zig
index 922c25ebc6..7265361b31 100644
--- a/lib/std/unicode/throughput_test.zig
+++ b/lib/std/unicode/throughput_test.zig
@@ -22,7 +22,7 @@ pub fn main() !void {
     const elapsed_ns_orig = timer.lap();
     @fence(.SeqCst);
 
-    var buffer2: [32767] u16 align(4096) = undefined;
+    var buffer2: [32767]u16 align(4096) = undefined;
     _ = try std.unicode.utf8ToUtf16Le_better(&buffer2, args[1]);
 
     @fence(.SeqCst);
diff --git a/test/compile_errors.zig b/test/compile_errors.zig
index f5798a5460..bf3ee14bec 100644
--- a/test/compile_errors.zig
+++ b/test/compile_errors.zig
@@ -2972,7 +2972,7 @@ pub fn addCases(cases: *tests.CompileErrorContext) void {
         \\    foo(bar);
         \\}
         \\
-        \\extern fn bar(x: *void) void { }
+        \\fn bar(x: *void) callconv(.C) void { }
         \\export fn entry2() void {
         \\    bar(&{});
         \\}
@@ -3871,7 +3871,7 @@ pub fn addCases(cases: *tests.CompileErrorContext) void {
         \\
         \\export fn entry() usize { return @sizeOf(@TypeOf(fns)); }
     , &[_][]const u8{
-        "tmp.zig:1:37: error: expected type 'fn(i32) i32', found 'extern fn(i32) i32'",
+        "tmp.zig:1:37: error: expected type 'fn(i32) i32', found 'fn(i32) callconv(.C) i32'",
     });
 
     cases.add("colliding invalid top level functions",
@@ -5618,7 +5618,7 @@ pub fn addCases(cases: *tests.CompileErrorContext) void {
     });
 
     cases.add("wrong types given to @export",
-        \\extern fn entry() void { }
+        \\fn entry() callconv(.C) void { }
         \\comptime {
         \\    @export("entry", entry, @as(u32, 1234));
         \\}
diff --git a/test/stage1/behavior/align.zig b/test/stage1/behavior/align.zig
index 1812394f2e..c83d2379b4 100644
--- a/test/stage1/behavior/align.zig
+++ b/test/stage1/behavior/align.zig
@@ -221,14 +221,14 @@ test "alignment of structs" {
     }) == @alignOf(usize));
 }
 
-test "alignment of extern() void" {
+test "alignment of function with c calling convention" {
     var runtime_nothing = nothing;
     const casted1 = @ptrCast(*const u8, runtime_nothing);
-    const casted2 = @ptrCast(extern fn () void, casted1);
+    const casted2 = @ptrCast(fn () callconv(.C) void, casted1);
     casted2();
 }
 
-extern fn nothing() void {}
+fn nothing() callconv(.C) void {}
 
 test "return error union with 128-bit integer" {
     expect(3 == try give());
diff --git a/test/stage1/behavior/bugs/1310.zig b/test/stage1/behavior/bugs/1310.zig
index f0f696e4bc..788cba5756 100644
--- a/test/stage1/behavior/bugs/1310.zig
+++ b/test/stage1/behavior/bugs/1310.zig
@@ -3,7 +3,7 @@ const expect = std.testing.expect;
 
 pub const VM = ?[*]const struct_InvocationTable_;
 pub const struct_InvocationTable_ = extern struct {
-    GetVM: ?extern fn (?[*]VM) c_int,
+    GetVM: ?fn (?[*]VM) callconv(.C) c_int,
 };
 
 pub const struct_VM_ = extern struct {
@@ -15,7 +15,7 @@ pub const struct_VM_ = extern struct {
 pub const InvocationTable_ = struct_InvocationTable_;
 pub const VM_ = struct_VM_;
 
-extern fn agent_callback(_vm: [*]VM, options: [*]u8) i32 {
+fn agent_callback(_vm: [*]VM, options: [*]u8) callconv(.C) i32 {
     return 11;
 }
 
diff --git a/test/stage1/behavior/cast.zig b/test/stage1/behavior/cast.zig
index aca8c6fc34..ae2530af61 100644
--- a/test/stage1/behavior/cast.zig
+++ b/test/stage1/behavior/cast.zig
@@ -477,7 +477,7 @@ test "compile time int to ptr of function" {
 }
 
 pub const FUNCTION_CONSTANT = @intToPtr(PFN_void, maxInt(usize));
-pub const PFN_void = extern fn (*c_void) void;
+pub const PFN_void = fn (*c_void) callconv(.C) void;
 
 fn foobar(func: PFN_void) void {
     std.testing.expect(@ptrToInt(func) == maxInt(usize));
@@ -587,7 +587,7 @@ test "peer cast *[0]T to []const T" {
 
 var global_array: [4]u8 = undefined;
 test "cast from array reference to fn" {
-    const f = @ptrCast(extern fn () void, &global_array);
+    const f = @ptrCast(fn () callconv(.C) void, &global_array);
     expect(@ptrToInt(f) == @ptrToInt(&global_array));
 }
 
diff --git a/test/stage1/behavior/misc.zig b/test/stage1/behavior/misc.zig
index 0b29189cde..9b9771a24c 100644
--- a/test/stage1/behavior/misc.zig
+++ b/test/stage1/behavior/misc.zig
@@ -19,7 +19,7 @@ comptime {
     @export("disabledExternFn", disabledExternFn, builtin.GlobalLinkage.Internal);
 }
 
-extern fn disabledExternFn() void {}
+fn disabledExternFn() callconv(.C) void {}
 
 test "call disabled extern fn" {
     disabledExternFn();
diff --git a/test/stage1/behavior/struct.zig b/test/stage1/behavior/struct.zig
index 2d51498a85..8e5ab29db3 100644
--- a/test/stage1/behavior/struct.zig
+++ b/test/stage1/behavior/struct.zig
@@ -580,7 +580,7 @@ test "default struct initialization fields" {
     expectEqual(1239, x.a + x.b);
 }
 
-test "extern fn returns struct by value" {
+test "fn with C calling convention returns struct by value" {
     const S = struct {
         fn entry() void {
             var x = makeBar(10);
@@ -591,7 +591,7 @@ test "extern fn returns struct by value" {
             handle: i32,
         };
 
-        extern fn makeBar(t: i32) ExternBar {
+        fn makeBar(t: i32) callconv(.C) ExternBar {
             return ExternBar{
                 .handle = t,
             };
diff --git a/test/standalone/load_dynamic_library/main.zig b/test/standalone/load_dynamic_library/main.zig
index d1cba72db5..197e3ca47c 100644
--- a/test/standalone/load_dynamic_library/main.zig
+++ b/test/standalone/load_dynamic_library/main.zig
@@ -9,7 +9,7 @@ pub fn main() !void {
     var lib = try std.DynLib.open(dynlib_name);
     defer lib.close();
 
-    const addFn = lib.lookup(extern fn (i32, i32) i32, "add") orelse return error.SymbolNotFound;
+    const addFn = lib.lookup(fn (i32, i32) callconv(.C) i32, "add") orelse return error.SymbolNotFound;
 
     const result = addFn(12, 34);
     std.debug.assert(result == 46);
diff --git a/test/translate_c.zig b/test/translate_c.zig
index c20989b835..a78c56fd73 100644
--- a/test/translate_c.zig
+++ b/test/translate_c.zig
@@ -238,7 +238,7 @@ pub fn addCases(cases: *tests.TranslateCContext) void {
         \\pub extern fn foo() void;
         \\pub export fn bar() void {
         \\    var func_ptr: ?*c_void = @ptrCast(?*c_void, foo);
-        \\    var typed_func_ptr: ?extern fn () void = @intToPtr(?extern fn () void, @intCast(c_ulong, @ptrToInt(func_ptr)));
+        \\    var typed_func_ptr: ?fn () callconv(.C) void = @intToPtr(?fn () callconv(.C) void, @intCast(c_ulong, @ptrToInt(func_ptr)));
         \\}
     });
 
@@ -2297,7 +2297,7 @@ pub fn addCases(cases: *tests.TranslateCContext) void {
         \\}
     , &[_][]const u8{
         \\pub fn bar() callconv(.C) void {}
-        \\pub export fn foo(arg_baz: ?extern fn () [*c]c_int) void {
+        \\pub export fn foo(arg_baz: ?fn () callconv(.C) [*c]c_int) void {
         \\    var baz = arg_baz;
         \\    bar();
         \\    _ = baz.?();