authorgravatar for luuk@degram.devLuuk de Gram <luuk@degram.dev> 2023-03-19 15:42:39+01:00
committergravatar for noreply@github.comGitHub <noreply@github.com> 2023-03-19 15:42:39+01:00
log322ace70f9fb5c3e8833255d1df033208c448349
tree1fbb00c9ca79b1c7bcb0cf16d8fbc17a1bd0c668
parent8f481dfc3c4f12327499485e3bf10fbbb1023186
parentd0fb1ef9625b55cc71b41438265f596a00d63749
signaturebadge-question-mark Signed by PGP key 4AEE18F83AFDEB23

Merge pull request #14838 from Luukdegram/bss-fix

wasm-linker: fix storing atoms in the correct segment

3 files changed, 91 insertions(+), 37 deletions(-)

src/link/Wasm.zig+12-3
......@@ -2828,22 +2828,31 @@ pub fn flushModule(wasm: *Wasm, comp: *Compilation, prog_node: *std.Progress.Nod
28282828 const decl = mod.declPtr(entry.key_ptr.*);
28292829 if (decl.isExtern()) continue;
28302830 const atom_index = entry.value_ptr.*;
2831 const atom = wasm.getAtomPtr(atom_index);
28312832 if (decl.ty.zigTypeTag() == .Fn) {
28322833 try wasm.parseAtom(atom_index, .function);
28332834 } else if (decl.getVariable()) |variable| {
28342835 if (!variable.is_mutable) {
28352836 try wasm.parseAtom(atom_index, .{ .data = .read_only });
28362837 } else if (variable.init.isUndefDeep()) {
2837 try wasm.parseAtom(atom_index, .{ .data = .uninitialized });
2838 // for safe build modes, we store the atom in the data segment,
2839 // whereas for unsafe build modes we store it in bss.
2840 const is_initialized = wasm.base.options.optimize_mode == .Debug or
2841 wasm.base.options.optimize_mode == .ReleaseSafe;
2842 try wasm.parseAtom(atom_index, .{ .data = if (is_initialized) .initialized else .uninitialized });
28382843 } else {
2839 try wasm.parseAtom(atom_index, .{ .data = .initialized });
2844 // when the decl is all zeroes, we store the atom in the bss segment,
2845 // in all other cases it will be in the data segment.
2846 const is_zeroes = for (atom.code.items) |byte| {
2847 if (byte != 0) break false;
2848 } else true;
2849 try wasm.parseAtom(atom_index, .{ .data = if (is_zeroes) .uninitialized else .initialized });
28402850 }
28412851 } else {
28422852 try wasm.parseAtom(atom_index, .{ .data = .read_only });
28432853 }
28442854
28452855 // also parse atoms for a decl's locals
2846 const atom = wasm.getAtomPtr(atom_index);
28472856 for (atom.locals.items) |local_atom_index| {
28482857 try wasm.parseAtom(local_atom_index, .{ .data = .read_only });
28492858 }
test/link/wasm/bss/build.zig+74-34
......@@ -6,38 +6,78 @@ pub fn build(b: *std.Build) void {
66 const test_step = b.step("test", "Test");
77 b.default_step = test_step;
88
9 const lib = b.addSharedLibrary(.{
10 .name = "lib",
11 .root_source_file = .{ .path = "lib.zig" },
12 .target = .{ .cpu_arch = .wasm32, .os_tag = .freestanding },
13 .optimize = .Debug,
14 });
15 lib.use_llvm = false;
16 lib.use_lld = false;
17 lib.strip = false;
18 // to make sure the bss segment is emitted, we must import memory
19 lib.import_memory = true;
20 lib.install();
21
22 const check_lib = lib.checkObject();
23
24 // since we import memory, make sure it exists with the correct naming
25 check_lib.checkStart("Section import");
26 check_lib.checkNext("entries 1");
27 check_lib.checkNext("module env"); // default module name is "env"
28 check_lib.checkNext("name memory"); // as per linker specification
29
30 // since we are importing memory, ensure it's not exported
31 check_lib.checkNotPresent("Section export");
32
33 // validate the name of the stack pointer
34 check_lib.checkStart("Section custom");
35 check_lib.checkNext("type data_segment");
36 check_lib.checkNext("names 2");
37 check_lib.checkNext("index 0");
38 check_lib.checkNext("name .rodata");
39 check_lib.checkNext("index 1"); // bss section always last
40 check_lib.checkNext("name .bss");
41
42 test_step.dependOn(&check_lib.step);
9 add(b, test_step, .Debug, true);
10 add(b, test_step, .ReleaseFast, false);
11 add(b, test_step, .ReleaseSmall, false);
12 add(b, test_step, .ReleaseSafe, true);
13}
14
15fn add(b: *std.Build, test_step: *std.Build.Step, optimize_mode: std.builtin.OptimizeMode, is_safe: bool) void {
16 {
17 const lib = b.addSharedLibrary(.{
18 .name = "lib",
19 .root_source_file = .{ .path = "lib.zig" },
20 .target = .{ .cpu_arch = .wasm32, .os_tag = .freestanding },
21 .optimize = optimize_mode,
22 });
23 lib.use_llvm = false;
24 lib.use_lld = false;
25 lib.strip = false;
26 // to make sure the bss segment is emitted, we must import memory
27 lib.import_memory = true;
28
29 const check_lib = lib.checkObject();
30
31 // since we import memory, make sure it exists with the correct naming
32 check_lib.checkStart("Section import");
33 check_lib.checkNext("entries 1");
34 check_lib.checkNext("module env"); // default module name is "env"
35 check_lib.checkNext("name memory"); // as per linker specification
36
37 // since we are importing memory, ensure it's not exported
38 check_lib.checkNotPresent("Section export");
39
40 // validate the name of the stack pointer
41 check_lib.checkStart("Section custom");
42 check_lib.checkNext("type data_segment");
43 check_lib.checkNext("names 2");
44 check_lib.checkNext("index 0");
45 check_lib.checkNext("name .rodata");
46 // for safe optimization modes `undefined` is stored in data instead of bss.
47 if (is_safe) {
48 check_lib.checkNext("index 1");
49 check_lib.checkNext("name .data");
50 check_lib.checkNotPresent("name .bss");
51 } else {
52 check_lib.checkNext("index 1"); // bss section always last
53 check_lib.checkNext("name .bss");
54 }
55 test_step.dependOn(&check_lib.step);
56 }
57
58 // verify zero'd declaration is stored in bss for all optimization modes.
59 {
60 const lib = b.addSharedLibrary(.{
61 .name = "lib",
62 .root_source_file = .{ .path = "lib2.zig" },
63 .target = .{ .cpu_arch = .wasm32, .os_tag = .freestanding },
64 .optimize = optimize_mode,
65 });
66 lib.use_llvm = false;
67 lib.use_lld = false;
68 lib.strip = false;
69 // to make sure the bss segment is emitted, we must import memory
70 lib.import_memory = true;
71
72 const check_lib = lib.checkObject();
73 check_lib.checkStart("Section custom");
74 check_lib.checkNext("type data_segment");
75 check_lib.checkNext("names 2");
76 check_lib.checkNext("index 0");
77 check_lib.checkNext("name .rodata");
78 check_lib.checkNext("index 1");
79 check_lib.checkNext("name .bss");
80
81 test_step.dependOn(&check_lib.step);
82 }
4383}
test/link/wasm/bss/lib2.zig created+5
......@@ -0,0 +1,5 @@
1pub var bss: u32 = 0;
2
3export fn foo() void {
4 _ = bss;
5}