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LibGC: Use mach_vm_map() for BlockAllocator on macOS

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This allows us to get a correctly aligned allocation with a single
syscall, unlike posix_memalign() which makes no such guarantees.
This commit is contained in:
Andreas Kling
2025-12-18 17:53:26 -06:00
committed by Andreas Kling
parent 82f63334d0
commit 5af4bc81e1
Notes: github-actions[bot] 2025-12-20 02:22:31 +00:00 
Author: https://github.com/awesomekling
Commit: https://github.com/LadybirdBrowser/ladybird/commit/5af4bc81e12
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/7187
1 changed files with 31 additions and 7 deletions
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38
Libraries/LibGC/BlockAllocator.cpp
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@@ -14,6 +14,11 @@
#include <LibGC/HeapBlock.h>
#include <sys/mman.h>
#if defined(AK_OS_MACOS)
# include <mach/mach.h>
# include <mach/mach_vm.h>
#endif
#ifdef HAS_ADDRESS_SANITIZER
# include <sanitizer/asan_interface.h>
# include <sanitizer/lsan_interface.h>
@@ -30,13 +35,16 @@ BlockAllocator::~BlockAllocator()
{
for (auto* block : m_blocks) {
ASAN_UNPOISON_MEMORY_REGION(block, HeapBlock::BLOCK_SIZE);
#if !defined(AK_OS_WINDOWS)
free(block);
#else
#if defined(AK_OS_MACOS)
kern_return_t kr = mach_vm_deallocate(mach_task_self(), reinterpret_cast<mach_vm_address_t>(block), HeapBlock::BLOCK_SIZE);
VERIFY(kr == KERN_SUCCESS);
#elif defined(AK_OS_WINDOWS)
if (!VirtualFree(block, 0, MEM_RELEASE)) {
warnln("{}", Error::from_windows_error());
VERIFY_NOT_REACHED();
}
#else
free(block);
#endif
}
}
@@ -58,13 +66,29 @@ void* BlockAllocator::allocate_block([[maybe_unused]] char const* name)
return block;
}
#if !defined(AK_OS_WINDOWS)
#if defined(AK_OS_MACOS)
mach_vm_address_t address = 0;
kern_return_t kr = mach_vm_map(
mach_task_self(),
&address,
HeapBlock::BLOCK_SIZE,
HeapBlock::BLOCK_SIZE - 1,
VM_FLAGS_ANYWHERE,
MEMORY_OBJECT_NULL,
0,
false,
VM_PROT_READ | VM_PROT_WRITE,
VM_PROT_READ | VM_PROT_WRITE,
VM_INHERIT_DEFAULT);
VERIFY(kr == KERN_SUCCESS);
auto* block = reinterpret_cast<void*>(address);
#elif defined(AK_OS_WINDOWS)
auto* block = VirtualAlloc(NULL, HeapBlock::BLOCK_SIZE, MEM_COMMIT, PAGE_READWRITE);
VERIFY(block);
#else
void* block = nullptr;
auto rc = posix_memalign(&block, HeapBlock::BLOCK_SIZE, HeapBlock::BLOCK_SIZE);
VERIFY(rc == 0);
#else
auto* block = VirtualAlloc(NULL, HeapBlock::BLOCK_SIZE, MEM_COMMIT, PAGE_READWRITE);
VERIFY(block);
#endif
LSAN_REGISTER_ROOT_REGION(block, HeapBlock::BLOCK_SIZE);
return block;