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LibC: Add malloc_size() to tell you how big an allocation might be.

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It can't be 100% precise but it doesn't really matter. Use this to implement
realloc() nicely. This also fixes a bug in realloc() where we didn't take
the size of the allocation metadata into account when computing the size of
an allocation backed by a BigAllocationBlock.
This commit is contained in:
Andreas Kling 2019-05-30 02:37:40 +02:00
parent a906098579
commit b160677e9e
2 changed files with 17 additions and 11 deletions
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27
LibC/malloc.cpp
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@ -155,9 +155,7 @@ void* malloc(size_t size)
}
}
#endif
char buffer[64];
snprintf(buffer, sizeof(buffer), "malloc: BigAllocationBlock(%u)", real_size);
auto* block = (BigAllocationBlock*)os_alloc(real_size, buffer);
auto* block = (BigAllocationBlock*)os_alloc(real_size, "malloc: BigAllocationBlock");
new (block) BigAllocationBlock(real_size);
return &block->m_slot[0];
}
@ -277,20 +275,27 @@ void* calloc(size_t count, size_t size)
return ptr;
}
size_t malloc_size(void* ptr)
{
if (!ptr)
return 0;
void* page_base = (void*)((uintptr_t)ptr & (uintptr_t)~0xfff);
auto* header = (const CommonHeader*)page_base;
auto size = header->m_size;
if (header->m_magic == MAGIC_BIGALLOC_HEADER)
size -= sizeof(CommonHeader);
return size;
}
void* realloc(void* ptr, size_t size)
{
if (!ptr)
return malloc(size);
size_t old_size = 0;
void* page_base = (void*)((uintptr_t)ptr & (uintptr_t)~0xfff);
auto* header = (const CommonHeader*)page_base;
old_size = header->m_size;
if (malloc_good_size(size) == old_size)
auto existing_allocation_size = malloc_size(ptr);
if (size <= existing_allocation_size)
return ptr;
auto* new_ptr = malloc(size);
memcpy(new_ptr, ptr, min(old_size, size));
memcpy(new_ptr, ptr, min(existing_allocation_size, size));
free(ptr);
return new_ptr;
}