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add comments on overriding in macOSX

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This commit is contained in:
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
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>
@ -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 malloc_introspection_t intro;
@ -326,6 +253,5 @@ static void __attribute__((constructor)) _mi_macos_override_malloc()
}
}
#endif
#endif // MI_MALLOC_OVERRIDE