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Merge pull request #14838 from Luukdegram/bss-fix

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wasm-linker: fix storing atoms in the correct segment
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Luuk de Gram 2023-03-19 15:42:39 +01:00 committed by GitHub
commit 322ace70f9
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3 changed files with 91 additions and 37 deletions
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15
src/link/Wasm.zig
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@ -2828,22 +2828,31 @@ pub fn flushModule(wasm: *Wasm, comp: *Compilation, prog_node: *std.Progress.Nod
const decl = mod.declPtr(entry.key_ptr.*);
if (decl.isExtern()) continue;
const atom_index = entry.value_ptr.*;
const atom = wasm.getAtomPtr(atom_index);
if (decl.ty.zigTypeTag() == .Fn) {
try wasm.parseAtom(atom_index, .function);
} else if (decl.getVariable()) |variable| {
if (!variable.is_mutable) {
try wasm.parseAtom(atom_index, .{ .data = .read_only });
} else if (variable.init.isUndefDeep()) {
try wasm.parseAtom(atom_index, .{ .data = .uninitialized });
// for safe build modes, we store the atom in the data segment,
// whereas for unsafe build modes we store it in bss.
const is_initialized = wasm.base.options.optimize_mode == .Debug or
wasm.base.options.optimize_mode == .ReleaseSafe;
try wasm.parseAtom(atom_index, .{ .data = if (is_initialized) .initialized else .uninitialized });
} else {
try wasm.parseAtom(atom_index, .{ .data = .initialized });
// when the decl is all zeroes, we store the atom in the bss segment,
// in all other cases it will be in the data segment.
const is_zeroes = for (atom.code.items) |byte| {
if (byte != 0) break false;
} else true;
try wasm.parseAtom(atom_index, .{ .data = if (is_zeroes) .uninitialized else .initialized });
}
} else {
try wasm.parseAtom(atom_index, .{ .data = .read_only });
}
// also parse atoms for a decl's locals
const atom = wasm.getAtomPtr(atom_index);
for (atom.locals.items) |local_atom_index| {
try wasm.parseAtom(local_atom_index, .{ .data = .read_only });
}

108
test/link/wasm/bss/build.zig
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@ -6,38 +6,78 @@ pub fn build(b: *std.Build) void {
const test_step = b.step("test", "Test");
b.default_step = test_step;
const lib = b.addSharedLibrary(.{
.name = "lib",
.root_source_file = .{ .path = "lib.zig" },
.target = .{ .cpu_arch = .wasm32, .os_tag = .freestanding },
.optimize = .Debug,
});
lib.use_llvm = false;
lib.use_lld = false;
lib.strip = false;
// to make sure the bss segment is emitted, we must import memory
lib.import_memory = true;
lib.install();
const check_lib = lib.checkObject();
// since we import memory, make sure it exists with the correct naming
check_lib.checkStart("Section import");
check_lib.checkNext("entries 1");
check_lib.checkNext("module env"); // default module name is "env"
check_lib.checkNext("name memory"); // as per linker specification
// since we are importing memory, ensure it's not exported
check_lib.checkNotPresent("Section export");
// validate the name of the stack pointer
check_lib.checkStart("Section custom");
check_lib.checkNext("type data_segment");
check_lib.checkNext("names 2");
check_lib.checkNext("index 0");
check_lib.checkNext("name .rodata");
check_lib.checkNext("index 1"); // bss section always last
check_lib.checkNext("name .bss");
test_step.dependOn(&check_lib.step);
add(b, test_step, .Debug, true);
add(b, test_step, .ReleaseFast, false);
add(b, test_step, .ReleaseSmall, false);
add(b, test_step, .ReleaseSafe, true);
}
fn add(b: *std.Build, test_step: *std.Build.Step, optimize_mode: std.builtin.OptimizeMode, is_safe: bool) void {
{
const lib = b.addSharedLibrary(.{
.name = "lib",
.root_source_file = .{ .path = "lib.zig" },
.target = .{ .cpu_arch = .wasm32, .os_tag = .freestanding },
.optimize = optimize_mode,
});
lib.use_llvm = false;
lib.use_lld = false;
lib.strip = false;
// to make sure the bss segment is emitted, we must import memory
lib.import_memory = true;
const check_lib = lib.checkObject();
// since we import memory, make sure it exists with the correct naming
check_lib.checkStart("Section import");
check_lib.checkNext("entries 1");
check_lib.checkNext("module env"); // default module name is "env"
check_lib.checkNext("name memory"); // as per linker specification
// since we are importing memory, ensure it's not exported
check_lib.checkNotPresent("Section export");
// validate the name of the stack pointer
check_lib.checkStart("Section custom");
check_lib.checkNext("type data_segment");
check_lib.checkNext("names 2");
check_lib.checkNext("index 0");
check_lib.checkNext("name .rodata");
// for safe optimization modes `undefined` is stored in data instead of bss.
if (is_safe) {
check_lib.checkNext("index 1");
check_lib.checkNext("name .data");
check_lib.checkNotPresent("name .bss");
} else {
check_lib.checkNext("index 1"); // bss section always last
check_lib.checkNext("name .bss");
}
test_step.dependOn(&check_lib.step);
}
// verify zero'd declaration is stored in bss for all optimization modes.
{
const lib = b.addSharedLibrary(.{
.name = "lib",
.root_source_file = .{ .path = "lib2.zig" },
.target = .{ .cpu_arch = .wasm32, .os_tag = .freestanding },
.optimize = optimize_mode,
});
lib.use_llvm = false;
lib.use_lld = false;
lib.strip = false;
// to make sure the bss segment is emitted, we must import memory
lib.import_memory = true;
const check_lib = lib.checkObject();
check_lib.checkStart("Section custom");
check_lib.checkNext("type data_segment");
check_lib.checkNext("names 2");
check_lib.checkNext("index 0");
check_lib.checkNext("name .rodata");
check_lib.checkNext("index 1");
check_lib.checkNext("name .bss");
test_step.dependOn(&check_lib.step);
}
}

5
test/link/wasm/bss/lib2.zig Normal file
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@ -0,0 +1,5 @@
pub var bss: u32 = 0;
export fn foo() void {
_ = bss;
}