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x64: use freeze/unfreeze api; TODO for PIE

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This commit is contained in:
Jakub Konka 2022-02-03 14:31:16 +01:00
parent e52af26856
commit f4e0641450
2 changed files with 34 additions and 26 deletions
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57
src/arch/x86_64/CodeGen.zig
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@ -1685,6 +1685,7 @@ fn airLoad(self: *Self, inst: Air.Inst.Index) !void {
fn store(self: *Self, ptr: MCValue, value: MCValue, ptr_ty: Type, value_ty: Type) InnerError!void {
_ = ptr_ty;
const abi_size = value_ty.abiSize(self.target.*);
switch (ptr) {
.none => unreachable,
.undef => unreachable,
@ -1705,6 +1706,9 @@ fn store(self: *Self, ptr: MCValue, value: MCValue, ptr_ty: Type, value_ty: Type
return self.fail("TODO implement storing to MCValue.embedded_in_code", .{});
},
.register => |reg| {
self.register_manager.freezeRegs(&.{reg});
defer self.register_manager.unfreezeRegs(&.{reg});
switch (value) {
.none => unreachable,
.undef => unreachable,
@ -1713,7 +1717,6 @@ fn store(self: *Self, ptr: MCValue, value: MCValue, ptr_ty: Type, value_ty: Type
.compare_flags_unsigned => unreachable,
.compare_flags_signed => unreachable,
.immediate => |imm| {
const abi_size = value_ty.abiSize(self.target.*);
switch (abi_size) {
1, 2, 4 => {
// TODO this is wasteful!
@ -1760,7 +1763,6 @@ fn store(self: *Self, ptr: MCValue, value: MCValue, ptr_ty: Type, value_ty: Type
}
},
.register => |src_reg| {
const abi_size = value_ty.abiSize(self.target.*);
_ = try self.addInst(.{
.tag = .mov,
.ops = (Mir.Ops{
@ -1777,9 +1779,16 @@ fn store(self: *Self, ptr: MCValue, value: MCValue, ptr_ty: Type, value_ty: Type
}
},
.memory => |addr| {
if (self.bin_file.options.pie) {
return self.fail("TODO implement storing to memory when targeting PIE", .{});
}
// TODO: in case the address fits in an imm32 we can use [ds:imm32]
// instead of wasting an instruction copying the address to a register
if (value.isRegister()) self.register_manager.freezeRegs(&.{value.register});
defer if (value.isRegister()) self.register_manager.unfreezeRegs(&.{value.register});
const addr_reg = try self.copyToTmpRegister(ptr_ty, .{ .immediate = addr });
// to get the actual address of the value we want to modify we have to go through the GOT
// mov reg, [reg]
@ -1793,37 +1802,39 @@ fn store(self: *Self, ptr: MCValue, value: MCValue, ptr_ty: Type, value_ty: Type
.data = .{ .imm = 0 },
});
const abi_size = value_ty.abiSize(self.target.*);
switch (value) {
.immediate => |imm| {
if (abi_size > 8) {
return self.fail("TODO saving imm to memory for abi_size {}", .{abi_size});
}
const payload = try self.addExtra(Mir.ImmPair{
.dest_off = 0,
.operand = @intCast(u32, imm),
});
const flags: u2 = switch (abi_size) {
1 => 0b00,
2 => 0b01,
4 => 0b10,
8 => 0b11,
else => unreachable,
};
if (flags == 0b11) {
const top_bits: u32 = @intCast(u32, imm >> 32);
const can_extend = if (value_ty.isUnsignedInt())
(top_bits == 0) and (imm & 0x8000_0000) == 0
else
top_bits == 0xffff_ffff;
if (!can_extend) {
return self.fail("TODO imm64 would get incorrectly sign extended", .{});
}
}
_ = try self.addInst(.{
.tag = .mov_mem_imm,
.ops = (Mir.Ops{
.reg1 = addr_reg.to64(),
.flags = switch (abi_size) {
1 => 0b00,
2 => 0b01,
4 => 0b10,
8 => flag: {
const top_bits: u32 = @intCast(u32, imm >> 32);
const can_extend = if (value_ty.isUnsignedInt())
(top_bits == 0) and (imm & 0x8000_0000) == 0
else
top_bits == 0xffff_ffff;
if (!can_extend) {
return self.fail("TODO imm64 would get incorrectly sign extended", .{});
}
break :flag 0b11;
},
else => {
return self.fail("TODO saving imm to memory for abi_size {}", .{abi_size});
},
},
.flags = flags,
}).encode(),
.data = .{ .payload = payload },
});

3
test/behavior/bugs/1486.zig
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@ -1,13 +1,10 @@
const std = @import("std");
const builtin = @import("builtin");
const expect = std.testing.expect;
const ptr = &global;
var global: usize = 123;
test "constant pointer to global variable causes runtime load" {
if (builtin.zig_backend == .stage2_x86_64) return error.SkipZigTest;
global = 1234;
try expect(&global == ptr);
try expect(ptr.* == 1234);