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deps(mimalloc): set MI_OVERRIDE=OFF on Windows #29467

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Merged
dylan-conway merged 2 commits into from
Apr 18, 2026
Merged

deps(mimalloc): set MI_OVERRIDE=OFF on Windows #29467

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deps(mimalloc): set MI_OVERRIDE=OFF on Windows
dylan-conway Apr 18, 2026
1432ab3
deps(mimalloc): add Windows row to override decision matrix
dylan-conway Apr 18, 2026
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22 changes: 13 additions & 9 deletions scripts/build/deps/mimalloc.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -59,13 +59,16 @@ export const mimalloc: Dependency = {

// ─── Override behavior (global malloc replacement) ───
// The decision matrix:
// ASAN: always OFF — ASAN interceptors must see the real malloc.
// macOS: OFF — macOS's malloc zones are sufficient and overriding
// causes issues with system frameworks (SecureTransport, etc.)
// that have their own allocator expectations.
// Linux: ON — this is the main win. All malloc/free goes through
// mimalloc, including WebKit's bmalloc when it falls back
// to system malloc.
// ASAN: always OFF — ASAN interceptors must see the real malloc.
// macOS: OFF — macOS's malloc zones are sufficient and overriding
// causes issues with system frameworks (SecureTransport, etc.)
// that have their own allocator expectations.
// Linux: ON — this is the main win. All malloc/free goes through
// mimalloc, including WebKit's bmalloc when it falls back
// to system malloc.
// Windows: OFF — Bun links the static CRT and calls mi_* directly;
// dev3's alloc-override.c emits _expand/_msize/free which
// duplicate against libucrt(d) at link time.
if (cfg.asan) {
args.MI_TRACK_ASAN = "ON";
args.MI_OVERRIDE = "OFF";
Expand All @@ -83,9 +86,10 @@ export const mimalloc: Dependency = {
args.MI_OVERRIDE = "ON";
args.MI_OSX_ZONE = "OFF";
args.MI_OSX_INTERPOSE = "OFF";
} else if (cfg.windows) {
// mimalloc's *default* is ON, so this must be explicit.
args.MI_OVERRIDE = "OFF";
}
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claude[bot] marked this conversation as resolved.
// Windows: use mimalloc's defaults (no override; Windows has its own
// mechanism via the static CRT we link).

if (cfg.debug) {
// Heavy debug checks: guard bytes, freed-memory poisoning, double-free
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