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Use mmap std.heap.page_allocator impl when compiling for Wasm + libc

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When linking libc, it should be the libc that manages the heap. The main
Wasm memory might have been configured as non-growable, which makes
`WasmAllocator` a poor default and causes the common `DebugAllocator`
use case fail with OOM errors unless the user uses `std_options` to
override the default page allocator. Additionally, on Emscripten,
growing Wasm memory without notifying the JS glue code will cause array
buffers to get detached and lead to spurious crashes.
This commit is contained in:
Carl Åstholm 2025-11-07 22:15:30 +01:00
parent d05156eb71
commit 3f1e290b45
3 changed files with 14 additions and 12 deletions
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15
lib/std/c.zig
View file

@ -1830,7 +1830,16 @@ pub const POLL = switch (native_os) {
/// Basic memory protection flags
pub const PROT = switch (native_os) {
.linux => linux.PROT,
.emscripten => emscripten.PROT,
// https://github.com/emscripten-core/emscripten/blob/08e2de1031913e4ba7963b1c56f35f036a7d4d56/system/lib/libc/musl/include/sys/mman.h#L57-L62
// lib/libc/include/wasm-wasi-musl/sys/mman.h
.emscripten, .wasi => struct {
pub const NONE = 0;
pub const READ = 1;
pub const WRITE = 2;
pub const EXEC = 4;
pub const GROWSDOWN = 0x01000000;
pub const GROWSUP = 0x02000000;
},
// https://github.com/SerenityOS/serenity/blob/6d59d4d3d9e76e39112842ec487840828f1c9bfe/Kernel/API/POSIX/sys/mman.h#L28-L31
.openbsd, .haiku, .dragonfly, .netbsd, .illumos, .freebsd, .windows, .serenity => struct {
/// page can not be accessed
@ -8692,7 +8701,9 @@ pub const O = switch (native_os) {
pub const MAP = switch (native_os) {
.linux => linux.MAP,
.emscripten => packed struct(u32) {
// https://github.com/emscripten-core/emscripten/blob/08e2de1031913e4ba7963b1c56f35f036a7d4d56/system/lib/libc/musl/include/sys/mman.h#L21-L39
// lib/libc/include/wasm-wasi-musl/sys/mman.h
.emscripten, .wasi => packed struct(u32) {
TYPE: enum(u4) {
SHARED = 0x01,
PRIVATE = 0x02,

2
lib/std/heap.zig
View file

@ -366,7 +366,7 @@ pub const page_allocator: Allocator = if (@hasDecl(root, "os") and
@hasDecl(root.os, "heap") and
@hasDecl(root.os.heap, "page_allocator"))
root.os.heap.page_allocator
else if (builtin.target.cpu.arch.isWasm()) .{
else if (builtin.target.cpu.arch.isWasm() and !builtin.link_libc) .{
.ptr = undefined,
.vtable = &WasmAllocator.vtable,
} else if (builtin.target.os.tag == .plan9) .{

9
lib/std/os/emscripten.zig
View file

@ -331,15 +331,6 @@ pub const POLL = struct {
pub const RDBAND = 0x080;
};
pub const PROT = struct {
pub const NONE = 0x0;
pub const READ = 0x1;
pub const WRITE = 0x2;
pub const EXEC = 0x4;
pub const GROWSDOWN = 0x01000000;
pub const GROWSUP = 0x02000000;
};
pub const rlim_t = u64;
pub const RLIM = struct {