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std: fix sentinel handling in Allocator interface

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Currently the only function that handles sentinel terminated slices
properly is free. All uses of mem.sliceAsBytes() in the allocator
interface lack proper handling of a possible sentinel.

This commit changes the Allocator interface to use @ptrCast() plus
the new mem.absorbSentinel() instead.

Reported-by: David Vanderson <david.vanderson@gmail.com>
References: https://github.com/ziglang/zig/pull/19984
References: https://github.com/ziglang/zig/pull/23020
This commit is contained in:
Isaac Freund
2025-03-26 14:12:25 +01:00
parent 3d16c1eb76
commit 4848c3a1ad
1 changed files with 4 additions and 5 deletions
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lib/std/mem/Allocator.zig
+4 -5
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@@ -322,7 +322,7 @@ pub fn resize(self: Allocator, allocation: anytype, new_len: usize) bool {
if (allocation.len == 0) {
return false;
}
const old_memory = mem.sliceAsBytes(allocation);
const old_memory: []u8 = @ptrCast(@constCast(mem.absorbSentinel(allocation)));
// I would like to use saturating multiplication here, but LLVM cannot lower it
// on WebAssembly: https://github.com/ziglang/zig/issues/9660
//const new_len_bytes = new_len *| @sizeOf(T);
@@ -368,7 +368,7 @@ pub fn remap(self: Allocator, allocation: anytype, new_len: usize) ?@TypeOf(allo
new_memory.len = new_len;
return new_memory;
}
const old_memory = mem.sliceAsBytes(allocation);
const old_memory: []u8 = @ptrCast(@constCast(mem.absorbSentinel(allocation)));
// I would like to use saturating multiplication here, but LLVM cannot lower it
// on WebAssembly: https://github.com/ziglang/zig/issues/9660
//const new_len_bytes = new_len *| @sizeOf(T);
@@ -420,7 +420,7 @@ pub fn reallocAdvanced(
return ptr;
}
const old_byte_slice = mem.sliceAsBytes(old_mem);
const old_byte_slice: []u8 = @ptrCast(@constCast(mem.absorbSentinel(old_mem)));
const byte_count = math.mul(usize, @sizeOf(T), new_n) catch return error.OutOfMemory;
// Note: can't set shrunk memory to undefined as memory shouldn't be modified on realloc failure
if (self.rawRemap(old_byte_slice, .fromByteUnits(slice_info.alignment orelse @alignOf(T)), byte_count, return_address)) |p| {
@@ -443,8 +443,7 @@ pub fn reallocAdvanced(
pub fn free(self: Allocator, memory: anytype) void {
const slice_info = @typeInfo(@TypeOf(memory)).pointer;
comptime assert(slice_info.size == .slice);
const mem_with_sent = memory[0 .. memory.len + @intFromBool(slice_info.sentinel() != null)];
const bytes: []u8 = @ptrCast(@constCast(mem_with_sent));
const bytes: []u8 = @ptrCast(@constCast(mem.absorbSentinel(memory)));
if (bytes.len == 0) return;
@memset(bytes, undefined);
self.rawFree(bytes, .fromByteUnits(slice_info.alignment orelse @alignOf(slice_info.child)), @returnAddress());