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wasm-linker: create TLS Wasm globals correctly

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Previously, they were only created when we had any TLS segment.
This meant that while the symbol existed, the global itself wouldn't.
The result of this was a crash during symbol names writing as it
would attempt to write the symbol name of a global that didn't exist.
Now we always create them, and instead update its `init` value during
`setupMemory`.

In the future, the entire symbol (and global) will be removed by
the garbage collector.
This commit is contained in:
Luuk de Gram 2023-07-18 19:55:20 +02:00
parent 1a3304ed23
commit 142dbc7b82
No known key found for this signature in database
GPG Key ID: A8CFE58E4DC7D664
2 changed files with 63 additions and 36 deletions
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40
src/link/Wasm.zig
View File

@ -410,7 +410,7 @@ pub fn openPath(allocator: Allocator, sub_path: []const u8, options: link.Option
},
);
} else {
symbol.index = @as(u32, @intCast(wasm_bin.imported_globals_count + wasm_bin.wasm_globals.items.len));
symbol.index = @intCast(wasm_bin.imported_globals_count + wasm_bin.wasm_globals.items.len);
symbol.setFlag(.WASM_SYM_VISIBILITY_HIDDEN);
const global = try wasm_bin.wasm_globals.addOne(allocator);
global.* = .{
@ -433,7 +433,7 @@ pub fn openPath(allocator: Allocator, sub_path: []const u8, options: link.Option
};
if (options.output_mode == .Obj or options.import_table) {
symbol.setUndefined(true);
symbol.index = @as(u32, @intCast(wasm_bin.imported_tables_count));
symbol.index = @intCast(wasm_bin.imported_tables_count);
wasm_bin.imported_tables_count += 1;
try wasm_bin.imports.put(allocator, loc, .{
.module_name = try wasm_bin.string_table.put(allocator, wasm_bin.host_name),
@ -467,16 +467,31 @@ pub fn openPath(allocator: Allocator, sub_path: []const u8, options: link.Option
const loc = try wasm_bin.createSyntheticSymbol("__tls_base", .global);
const symbol = loc.getSymbol(wasm_bin);
symbol.setFlag(.WASM_SYM_VISIBILITY_HIDDEN);
symbol.index = @intCast(wasm_bin.imported_globals_count + wasm_bin.wasm_globals.items.len);
try wasm_bin.wasm_globals.append(wasm_bin.base.allocator, .{
.global_type = .{ .valtype = .i32, .mutable = true },
.init = .{ .i32_const = undefined },
});
}
{
const loc = try wasm_bin.createSyntheticSymbol("__tls_size", .global);
const symbol = loc.getSymbol(wasm_bin);
symbol.setFlag(.WASM_SYM_VISIBILITY_HIDDEN);
symbol.index = @intCast(wasm_bin.imported_globals_count + wasm_bin.wasm_globals.items.len);
try wasm_bin.wasm_globals.append(wasm_bin.base.allocator, .{
.global_type = .{ .valtype = .i32, .mutable = false },
.init = .{ .i32_const = undefined },
});
}
{
const loc = try wasm_bin.createSyntheticSymbol("__tls_align", .global);
const symbol = loc.getSymbol(wasm_bin);
symbol.setFlag(.WASM_SYM_VISIBILITY_HIDDEN);
symbol.index = @intCast(wasm_bin.imported_globals_count + wasm_bin.wasm_globals.items.len);
try wasm_bin.wasm_globals.append(wasm_bin.base.allocator, .{
.global_type = .{ .valtype = .i32, .mutable = false },
.init = .{ .i32_const = undefined },
});
}
{
const loc = try wasm_bin.createSyntheticSymbol("__wasm_init_tls", .function);
@ -2757,27 +2772,18 @@ fn setupMemory(wasm: *Wasm) !void {
if (mem.eql(u8, entry.key_ptr.*, ".tdata")) {
if (wasm.findGlobalSymbol("__tls_size")) |loc| {
const sym = loc.getSymbol(wasm);
sym.index = @as(u32, @intCast(wasm.wasm_globals.items.len)) + wasm.imported_globals_count;
try wasm.wasm_globals.append(wasm.base.allocator, .{
.global_type = .{ .valtype = .i32, .mutable = false },
.init = .{ .i32_const = @as(i32, @intCast(segment.size)) },
});
wasm.wasm_globals.items[sym.index - wasm.imported_globals_count].init.i32_const = @intCast(segment.size);
}
if (wasm.findGlobalSymbol("__tls_align")) |loc| {
const sym = loc.getSymbol(wasm);
sym.index = @as(u32, @intCast(wasm.wasm_globals.items.len)) + wasm.imported_globals_count;
try wasm.wasm_globals.append(wasm.base.allocator, .{
.global_type = .{ .valtype = .i32, .mutable = false },
.init = .{ .i32_const = @as(i32, @intCast(segment.alignment)) },
});
wasm.wasm_globals.items[sym.index - wasm.imported_globals_count].init.i32_const = @intCast(segment.alignment);
}
if (wasm.findGlobalSymbol("__tls_base")) |loc| {
const sym = loc.getSymbol(wasm);
sym.index = @as(u32, @intCast(wasm.wasm_globals.items.len)) + wasm.imported_globals_count;
try wasm.wasm_globals.append(wasm.base.allocator, .{
.global_type = .{ .valtype = .i32, .mutable = wasm.base.options.shared_memory },
.init = .{ .i32_const = if (wasm.base.options.shared_memory) @as(u32, 0) else @as(i32, @intCast(memory_ptr)) },
});
wasm.wasm_globals.items[sym.index - wasm.imported_globals_count].init.i32_const = if (wasm.base.options.shared_memory)
@as(i32, 0)
else
@as(i32, @intCast(memory_ptr));
}
}

59
test/link/wasm/shared-memory/build.zig
View File

@ -5,11 +5,9 @@ pub fn build(b: *std.Build) void {
b.default_step = test_step;
add(b, test_step, .Debug);
// Enable the following build modes once garbage-collection is implemented properly.
// add(b, test_step, .ReleaseFast);
// add(b, test_step, .ReleaseSmall);
// add(b, test_step, .ReleaseSafe);
add(b, test_step, .ReleaseFast);
add(b, test_step, .ReleaseSmall);
add(b, test_step, .ReleaseSafe);
}
fn add(b: *std.Build, test_step: *std.Build.Step, optimize_mode: std.builtin.OptimizeMode) void {
@ -47,30 +45,53 @@ fn add(b: *std.Build, test_step: *std.Build.Step, optimize_mode: std.builtin.Opt
// This section *must* be emit as the start function is set to the index
// of __wasm_init_memory
check_lib.checkStart("Section start");
// release modes will have the TLS segment optimized out in our test-case.
// This means we won't have __wasm_init_memory in such case, and therefore
// should also not have a section "start"
if (optimize_mode == .Debug) {
check_lib.checkStart("Section start");
}
// This section is only and *must* be emit when shared-memory is enabled
check_lib.checkStart("Section data_count");
check_lib.checkNext("count 3");
// release modes will have the TLS segment optimized out in our test-case.
if (optimize_mode == .Debug) {
check_lib.checkStart("Section data_count");
check_lib.checkNext("count 3");
}
check_lib.checkStart("Section custom");
check_lib.checkNext("name name");
check_lib.checkNext("type function");
check_lib.checkNext("name __wasm_init_memory");
if (optimize_mode == .Debug) {
check_lib.checkNext("name __wasm_init_memory");
}
check_lib.checkNext("name __wasm_init_tls");
check_lib.checkNext("type global");
check_lib.checkNext("name __tls_size");
check_lib.checkNext("name __tls_align");
check_lib.checkNext("name __tls_base");
// In debug mode the symbol __tls_base is resolved to an undefined symbol
// from the object file, hence its placement differs than in release modes
// where the entire tls segment is optimized away, and tls_base will have
// its original position.
if (optimize_mode == .Debug) {
check_lib.checkNext("name __tls_size");
check_lib.checkNext("name __tls_align");
check_lib.checkNext("name __tls_base");
} else {
check_lib.checkNext("name __tls_base");
check_lib.checkNext("name __tls_size");
check_lib.checkNext("name __tls_align");
}
check_lib.checkNext("type data_segment");
check_lib.checkNext("names 3");
check_lib.checkNext("index 0");
check_lib.checkNext("name .rodata");
check_lib.checkNext("index 1");
check_lib.checkNext("name .bss");
check_lib.checkNext("index 2");
check_lib.checkNext("name .tdata");
if (optimize_mode == .Debug) {
check_lib.checkNext("names 3");
check_lib.checkNext("index 0");
check_lib.checkNext("name .rodata");
check_lib.checkNext("index 1");
check_lib.checkNext("name .bss");
check_lib.checkNext("index 2");
check_lib.checkNext("name .tdata");
}
test_step.dependOn(&check_lib.step);
}