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Some improvements to LibC malloc().

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This commit is contained in:
Andreas Kling 2018-11-19 01:40:19 +01:00
parent 85649077cd
commit 526dcafd57
Notes: sideshowbarker 2024-07-19 16:09:43 +09:00
1 changed files with 37 additions and 33 deletions
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70
LibC/stdlib.cpp
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@ -10,19 +10,25 @@
extern "C" {
#define SANITIZE_LIBC_MALLOC
#define MALLOC_SCRUB_BYTE 0x85
#define FREE_SCRUB_BYTE 0x82
struct MallocHeader {
uint16_t magic;
uint16_t first_chunk_index;
uint16_t chunk_count;
uint16_t xorcheck;
size_t size;
uint32_t compute_xorcheck() const
{
return 0x19820413 ^ ((first_chunk_index << 16) | chunk_count) ^ size;
}
};
#define MALLOC_MAGIC 0x0413 // happy birthday k
#define CHUNK_SIZE 32
struct MallocFooter {
uint32_t xorcheck;
};
#define CHUNK_SIZE 8
#define POOL_SIZE 128 * 1024
static const size_t malloc_budget = POOL_SIZE;
@ -35,7 +41,7 @@ static uint32_t s_malloc_sum_free = POOL_SIZE;
void* malloc(size_t size)
{
// We need space for the MallocHeader structure at the head of the block.
size_t real_size = size + sizeof(MallocHeader);
size_t real_size = size + sizeof(MallocHeader) + sizeof(MallocFooter);
if (s_malloc_sum_free < real_size) {
fprintf(stderr, "malloc(): Out of memory\ns_malloc_sum_free=%u, real_size=%x\n", s_malloc_sum_free, real_size);
@ -72,17 +78,18 @@ void* malloc(size_t size)
byte* ptr = ((byte*)header) + sizeof(MallocHeader);
header->chunk_count = chunks_needed;
header->first_chunk_index = first_chunk;
header->magic = MALLOC_MAGIC;
header->xorcheck = header->magic ^ header->first_chunk_index ^ header->chunk_count;
header->size = size;
auto* footer = (MallocFooter*)((byte*)header + (header->chunk_count * CHUNK_SIZE) - sizeof(MallocFooter));
footer->xorcheck = header->compute_xorcheck();
for (size_t k = first_chunk; k < (first_chunk + chunks_needed); ++k)
s_malloc_map[k / 8] |= 1 << (k % 8);
s_malloc_sum_alloc += header->chunk_count * CHUNK_SIZE;
s_malloc_sum_free -= header->chunk_count * CHUNK_SIZE;
#ifdef SANITIZE_LIBC_MALLOC
memset(ptr, MALLOC_SCRUB_BYTE, (header->chunk_count * CHUNK_SIZE) - sizeof(MallocHeader));
#endif
memset(ptr, MALLOC_SCRUB_BYTE, (header->chunk_count * CHUNK_SIZE) - (sizeof(MallocHeader) + sizeof(MallocFooter)));
return ptr;
}
}
@ -100,30 +107,35 @@ void* malloc(size_t size)
return nullptr;
}
void free(void *ptr)
static void validate_mallocation(void* ptr, const char* func)
{
auto* header = (MallocHeader*)((((byte*)ptr) - sizeof(MallocHeader)));
if (header->size == 0) {
fprintf(stderr, "%s called on bad pointer %p, size=0\n", func, ptr);
assert(false);
}
auto* footer = (MallocFooter*)((byte*)header + (header->chunk_count * CHUNK_SIZE) - sizeof(MallocFooter));
uint32_t expected_xorcheck = header->compute_xorcheck();
if (footer->xorcheck != expected_xorcheck) {
fprintf(stderr, "%s called on bad pointer %p, xorcheck=%w (expected %w)\n", func, ptr, footer->xorcheck, expected_xorcheck);
assert(false);
}
}
void free(void* ptr)
{
if (!ptr)
return;
validate_mallocation(ptr, "free()");
auto* header = (MallocHeader*)((((byte*)ptr) - sizeof(MallocHeader)));
if (header->magic != MALLOC_MAGIC) {
fprintf(stderr, "free() called on bad pointer %p, magic=%w\n", ptr, header->magic);
assert(false);
}
if (header->xorcheck != (header->magic ^ header->first_chunk_index ^ header->chunk_count)) {
fprintf(stderr, "free() called on bad pointer %p, xorcheck=%w\n", ptr, header->xorcheck);
assert(false);
}
for (unsigned i = header->first_chunk_index; i < (header->first_chunk_index + header->chunk_count); ++i)
s_malloc_map[i / 8] &= ~(1 << (i % 8));
s_malloc_sum_alloc -= header->chunk_count * CHUNK_SIZE;
s_malloc_sum_free += header->chunk_count * CHUNK_SIZE;
#ifdef SANITIZE_LIBC_MALLOC
memset(header, FREE_SCRUB_BYTE, header->chunk_count * CHUNK_SIZE);
#endif
}
void __malloc_init()
@ -143,17 +155,9 @@ void* calloc(size_t nmemb, size_t)
void* realloc(void *ptr, size_t size)
{
validate_mallocation(ptr, "realloc()");
auto* header = (MallocHeader*)((((byte*)ptr) - sizeof(MallocHeader)));
if (header->magic != MALLOC_MAGIC) {
fprintf(stderr, "realloc() called on bad pointer %p, magic=%w\n", ptr, header->magic);
assert(false);
}
if (header->xorcheck != (header->magic ^ header->first_chunk_index ^ header->chunk_count)) {
fprintf(stderr, "realloc() called on bad pointer %p, xorcheck=%w\n", ptr, header->xorcheck);
assert(false);
}
size_t old_size = header->chunk_count * CHUNK_SIZE;
size_t old_size = header->size;
auto* new_ptr = malloc(size);
memcpy(new_ptr, ptr, old_size);
return new_ptr;