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wasm linker: fix corruption of string bytes

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if any fixups are emitted in lowering data, keep the string bytes
allocated even if all zeroes because it is used as a fixup staging area.
This commit is contained in:
Andrew Kelley 2025-01-10 19:08:44 -08:00
parent 9c14645b58
commit e18a397c85
1 changed files with 16 additions and 8 deletions
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24
src/link/Wasm.zig
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@ -3064,7 +3064,8 @@ pub fn updateFunc(wasm: *Wasm, pt: Zcu.PerThread, func_index: InternPool.Index,
dev.check(.wasm_backend);
const gpa = pt.zcu.gpa;
const zcu = pt.zcu;
const gpa = zcu.gpa;
try wasm.functions.ensureUnusedCapacity(gpa, 1);
try wasm.zcu_funcs.ensureUnusedCapacity(gpa, 1);
@ -3074,9 +3075,8 @@ pub fn updateFunc(wasm: *Wasm, pt: Zcu.PerThread, func_index: InternPool.Index,
// That lowering happens during `flush`, after garbage collection, which
// can affect function and global indexes, which affects the LEB integer
// encoding, which affects the output binary size.
wasm.zcu_funcs.putAssumeCapacity(func_index, .{
.function = try CodeGen.function(wasm, pt, func_index, air, liveness),
});
const function = try CodeGen.function(wasm, pt, func_index, air, liveness);
wasm.zcu_funcs.putAssumeCapacity(func_index, .{ .function = function });
wasm.functions.putAssumeCapacity(.pack(wasm, .{ .zcu_func = @enumFromInt(wasm.zcu_funcs.entries.len - 1) }), {});
try zds.finish(wasm, pt);
@ -3356,7 +3356,7 @@ pub fn prelink(wasm: *Wasm, prog_node: std.Progress.Node) link.File.FlushError!v
}
}
fn markFunctionImport(
pub fn markFunctionImport(
wasm: *Wasm,
name: String,
import: *FunctionImport,
@ -4455,12 +4455,19 @@ pub fn isBss(wasm: *const Wasm, optional_name: OptionalString) bool {
fn lowerZcuData(wasm: *Wasm, pt: Zcu.PerThread, ip_index: InternPool.Index) !ZcuDataObj {
const code_start: u32 = @intCast(wasm.string_bytes.items.len);
const relocs_start: u32 = @intCast(wasm.out_relocs.len);
const uav_fixups_start: u32 = @intCast(wasm.uav_fixups.items.len);
const nav_fixups_start: u32 = @intCast(wasm.nav_fixups.items.len);
const func_table_fixups_start: u32 = @intCast(wasm.func_table_fixups.items.len);
wasm.string_bytes_lock.lock();
try codegen.generateSymbol(&wasm.base, pt, .unneeded, .fromInterned(ip_index), &wasm.string_bytes, .none);
const code_len: u32 = @intCast(wasm.string_bytes.items.len - code_start);
const relocs_len: u32 = @intCast(wasm.out_relocs.len - relocs_start);
const any_fixups =
uav_fixups_start != wasm.uav_fixups.items.len or
nav_fixups_start != wasm.nav_fixups.items.len or
func_table_fixups_start != wasm.func_table_fixups.items.len;
wasm.string_bytes_lock.unlock();
const naive_code: DataPayload = .{
@ -4469,8 +4476,9 @@ fn lowerZcuData(wasm: *Wasm, pt: Zcu.PerThread, ip_index: InternPool.Index) !Zcu
};
// Only nonzero init values need to take up space in the output.
const all_zeroes = std.mem.allEqual(u8, naive_code.slice(wasm), 0);
const code: DataPayload = if (!all_zeroes) naive_code else c: {
// If any fixups are present, we still need the string bytes allocated since
// that is the staging area for the fixups.
const code: DataPayload = if (!any_fixups and std.mem.allEqual(u8, naive_code.slice(wasm), 0)) c: {
wasm.string_bytes.shrinkRetainingCapacity(code_start);
// Indicate empty by making off and len the same value, however, still
// transmit the data size by using the size as that value.
@ -4478,7 +4486,7 @@ fn lowerZcuData(wasm: *Wasm, pt: Zcu.PerThread, ip_index: InternPool.Index) !Zcu
.off = .none,
.len = naive_code.len,
};
};
} else naive_code;
return .{
.code = code,