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add comments on overriding in macOSX

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daan 2020-02-09 18:26:50 -08:00
parent 9062f39764
commit afe434463a
1 changed files with 6 additions and 80 deletions
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86
src/alloc-override-osx.c
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@ -17,6 +17,12 @@ terms of the MIT license. A copy of the license can be found in the file
/* ------------------------------------------------------ /* ------------------------------------------------------
Override system malloc on macOS Override system malloc on macOS
This is done through the malloc zone interface. This is done through the malloc zone interface.
It seems we also need to interpose (see `alloc-override.c`)
or otherwise we get zone errors as there are usually
already allocations done by the time we take over the
zone. Unfortunately, that means we need to replace
the `free` with a checked free (`cfree`) impacting
performance.
------------------------------------------------------ */ ------------------------------------------------------ */
#include <AvailabilityMacros.h> #include <AvailabilityMacros.h>
@ -181,85 +187,6 @@ static malloc_zone_t* mi_get_default_zone()
} }
} }
#if 0
// directly overwrite the default zone as per:
// <https://lists.apple.com/archives/darwin-dev/2005/Apr/msg00050.html>
#include <mach/mach.h>
static void __attribute__((constructor)) _mi_macos_override_malloc_direct()
{
static malloc_introspection_t intro;
memset(&intro, 0, sizeof(intro));
intro.enumerator = &intro_enumerator;
intro.good_size = &intro_good_size;
intro.check = &intro_check;
intro.print = &intro_print;
intro.log = &intro_log;
intro.force_lock = &intro_force_lock;
intro.force_unlock = &intro_force_unlock;
static malloc_zone_t oldzone;
static malloc_zone_t* zone;
zone = mi_get_default_zone(); // get the `malloc` backing default zone
if (zone == NULL) return;
// save the default zone in oldzone
memset(&oldzone, 0, sizeof(oldzone));
if (zone->version >= 9) memcpy(&oldzone, zone, sizeof(oldzone));
if (zone->version >= 8) {
vm_protect(mach_task_self(), (uintptr_t)zone, sizeof(*zone), 0,
VM_PROT_READ|VM_PROT_WRITE);
}
// overwrite default zone functions in-place
zone->zone_name = "mimalloc";
zone->size = &zone_size;
zone->introspect = &intro;
zone->malloc = &zone_malloc;
zone->calloc = &zone_calloc;
zone->valloc = &zone_valloc;
zone->free = &zone_free;
zone->realloc = &zone_realloc;
zone->destroy = &zone_destroy;
zone->batch_malloc = &zone_batch_malloc;
zone->batch_free = &zone_batch_free;
malloc_zone_t* purgeable_zone = NULL;
#if defined(MAC_OS_X_VERSION_10_6) && \
MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_6
// switch to version 9 on OSX 10.6 to support memalign.
// zone->version = 9;
zone->memalign = &zone_memalign;
zone->free_definite_size = &zone_free_definite_size;
zone->pressure_relief = &zone_pressure_relief;
intro.zone_locked = &intro_zone_locked;
intro.statistics = &intro_statistics;
/*
// force the purgeable zone to exist to avoid strange bugs
if (malloc_default_purgeable_zone) {
purgeable_zone = malloc_default_purgeable_zone();
}
*/
#endif
if (zone->version >= 8) {
vm_protect(mach_task_self(), (uintptr_t)zone, sizeof(*zone), 0,
VM_PROT_READ);
}
/*
// Unregister, and re-register the purgeable_zone to avoid bugs if it occurs
// earlier than the default zone.
if (purgeable_zone != NULL) {
malloc_zone_unregister(purgeable_zone);
malloc_zone_register(purgeable_zone);
}
*/
}
#else
static void __attribute__((constructor)) _mi_macos_override_malloc() static void __attribute__((constructor)) _mi_macos_override_malloc()
{ {
static malloc_introspection_t intro; static malloc_introspection_t intro;
@ -326,6 +253,5 @@ static void __attribute__((constructor)) _mi_macos_override_malloc()
} }
} }
#endif
#endif // MI_MALLOC_OVERRIDE #endif // MI_MALLOC_OVERRIDE