glibc 2.23버전에서 malloc의 동작과정을 살펴보았기 때문에 해당 과정에 대한 이해가 있다라고 생각하고 바뀐 코드 위주로 정리할 것이다
각 소제목에 해당되는 상세 설명은 각 리스트 아래 더보기 참고
전체 코드는 아래 더보기
더보기
static void *
_int_malloc (mstate av, size_t bytes)
{
INTERNAL_SIZE_T nb; /* normalized request size */
unsigned int idx; /* associated bin index */
mbinptr bin; /* associated bin */
mchunkptr victim; /* inspected/selected chunk */
INTERNAL_SIZE_T size; /* its size */
int victim_index; /* its bin index */
mchunkptr remainder; /* remainder from a split */
unsigned long remainder_size; /* its size */
unsigned int block; /* bit map traverser */
unsigned int bit; /* bit map traverser */
unsigned int map; /* current word of binmap */
mchunkptr fwd; /* misc temp for linking */
mchunkptr bck; /* misc temp for linking */
#if USE_TCACHE
size_t tcache_unsorted_count; /* count of unsorted chunks processed */
#endif
const char *errstr = NULL;
/*
Convert request size to internal form by adding SIZE_SZ bytes
overhead plus possibly more to obtain necessary alignment and/or
to obtain a size of at least MINSIZE, the smallest allocatable
size. Also, checked_request2size traps (returning 0) request sizes
that are so large that they wrap around zero when padded and
aligned.
*/
checked_request2size (bytes, nb);
/* There are no usable arenas. Fall back to sysmalloc to get a chunk from
mmap. */
if (__glibc_unlikely (av == NULL))
{
void *p = sysmalloc (nb, av);
if (p != NULL)
alloc_perturb (p, bytes);
return p;
}
/*
If the size qualifies as a fastbin, first check corresponding bin.
This code is safe to execute even if av is not yet initialized, so we
can try it without checking, which saves some time on this fast path.
*/
#define REMOVE_FB(fb, victim, pp) \
do \
{ \
victim = pp; \
if (victim == NULL) \
break; \
} \
while ((pp = catomic_compare_and_exchange_val_acq (fb, victim->fd, victim)) \
!= victim); \
if ((unsigned long) (nb) <= (unsigned long) (get_max_fast ()))
{
idx = fastbin_index (nb);
mfastbinptr *fb = &fastbin (av, idx);
mchunkptr pp = *fb;
REMOVE_FB (fb, victim, pp);
if (victim != 0)
{
if (__builtin_expect (fastbin_index (chunksize (victim)) != idx, 0))
{
errstr = "malloc(): memory corruption (fast)";
errout:
malloc_printerr (check_action, errstr, chunk2mem (victim), av);
return NULL;
}
check_remalloced_chunk (av, victim, nb);
#if USE_TCACHE
/* While we're here, if we see other chunks of the same size,
stash them in the tcache. */
size_t tc_idx = csize2tidx (nb);
if (tcache && tc_idx < mp_.tcache_bins)
{
mchunkptr tc_victim;
/* While bin not empty and tcache not full, copy chunks over. */
while (tcache->counts[tc_idx] < mp_.tcache_count
&& (pp = *fb) != NULL)
{
REMOVE_FB (fb, tc_victim, pp);
if (tc_victim != 0)
{
tcache_put (tc_victim, tc_idx);
}
}
}
#endif
void *p = chunk2mem (victim);
alloc_perturb (p, bytes);
return p;
}
}
/*
If a small request, check regular bin. Since these "smallbins"
hold one size each, no searching within bins is necessary.
(For a large request, we need to wait until unsorted chunks are
processed to find best fit. But for small ones, fits are exact
anyway, so we can check now, which is faster.)
*/
if (in_smallbin_range (nb))
{
idx = smallbin_index (nb);
bin = bin_at (av, idx);
if ((victim = last (bin)) != bin)
{
if (victim == 0) /* initialization check */
malloc_consolidate (av);
else
{
bck = victim->bk;
if (__glibc_unlikely (bck->fd != victim))
{
errstr = "malloc(): smallbin double linked list corrupted";
goto errout;
}
set_inuse_bit_at_offset (victim, nb);
bin->bk = bck;
bck->fd = bin;
if (av != &main_arena)
set_non_main_arena (victim);
check_malloced_chunk (av, victim, nb);
#if USE_TCACHE
/* While we're here, if we see other chunks of the same size,
stash them in the tcache. */
size_t tc_idx = csize2tidx (nb);
if (tcache && tc_idx < mp_.tcache_bins)
{
mchunkptr tc_victim;
/* While bin not empty and tcache not full, copy chunks over. */
while (tcache->counts[tc_idx] < mp_.tcache_count
&& (tc_victim = last (bin)) != bin)
{
if (tc_victim != 0)
{
bck = tc_victim->bk;
set_inuse_bit_at_offset (tc_victim, nb);
if (av != &main_arena)
set_non_main_arena (tc_victim);
bin->bk = bck;
bck->fd = bin;
tcache_put (tc_victim, tc_idx);
}
}
}
#endif
void *p = chunk2mem (victim);
alloc_perturb (p, bytes);
return p;
}
}
}
/*
If this is a large request, consolidate fastbins before continuing.
While it might look excessive to kill all fastbins before
even seeing if there is space available, this avoids
fragmentation problems normally associated with fastbins.
Also, in practice, programs tend to have runs of either small or
large requests, but less often mixtures, so consolidation is not
invoked all that often in most programs. And the programs that
it is called frequently in otherwise tend to fragment.
*/
else
{
idx = largebin_index (nb);
if (have_fastchunks (av))
malloc_consolidate (av);
}
/*
Process recently freed or remaindered chunks, taking one only if
it is exact fit, or, if this a small request, the chunk is remainder from
the most recent non-exact fit. Place other traversed chunks in
bins. Note that this step is the only place in any routine where
chunks are placed in bins.
The outer loop here is needed because we might not realize until
near the end of malloc that we should have consolidated, so must
do so and retry. This happens at most once, and only when we would
otherwise need to expand memory to service a "small" request.
*/
#if USE_TCACHE
INTERNAL_SIZE_T tcache_nb = 0;
size_t tc_idx = csize2tidx (nb);
if (tcache && tc_idx < mp_.tcache_bins)
tcache_nb = nb;
int return_cached = 0;
tcache_unsorted_count = 0;
#endif
for (;; )
{
int iters = 0;
while ((victim = unsorted_chunks (av)->bk) != unsorted_chunks (av))
{
bck = victim->bk;
if (__builtin_expect (chunksize_nomask (victim) <= 2 * SIZE_SZ, 0)
|| __builtin_expect (chunksize_nomask (victim)
> av->system_mem, 0))
malloc_printerr (check_action, "malloc(): memory corruption",
chunk2mem (victim), av);
size = chunksize (victim);
/*
If a small request, try to use last remainder if it is the
only chunk in unsorted bin. This helps promote locality for
runs of consecutive small requests. This is the only
exception to best-fit, and applies only when there is
no exact fit for a small chunk.
*/
if (in_smallbin_range (nb) &&
bck == unsorted_chunks (av) &&
victim == av->last_remainder &&
(unsigned long) (size) > (unsigned long) (nb + MINSIZE))
{
/* split and reattach remainder */
remainder_size = size - nb;
remainder = chunk_at_offset (victim, nb);
unsorted_chunks (av)->bk = unsorted_chunks (av)->fd = remainder;
av->last_remainder = remainder;
remainder->bk = remainder->fd = unsorted_chunks (av);
if (!in_smallbin_range (remainder_size))
{
remainder->fd_nextsize = NULL;
remainder->bk_nextsize = NULL;
}
set_head (victim, nb | PREV_INUSE |
(av != &main_arena ? NON_MAIN_ARENA : 0));
set_head (remainder, remainder_size | PREV_INUSE);
set_foot (remainder, remainder_size);
check_malloced_chunk (av, victim, nb);
void *p = chunk2mem (victim);
alloc_perturb (p, bytes);
return p;
}
/* remove from unsorted list */
unsorted_chunks (av)->bk = bck;
bck->fd = unsorted_chunks (av);
/* Take now instead of binning if exact fit */
if (size == nb)
{
set_inuse_bit_at_offset (victim, size);
if (av != &main_arena)
set_non_main_arena (victim);
#if USE_TCACHE
/* Fill cache first, return to user only if cache fills.
We may return one of these chunks later. */
if (tcache_nb
&& tcache->counts[tc_idx] < mp_.tcache_count)
{
tcache_put (victim, tc_idx);
return_cached = 1;
continue;
}
else
{
#endif
check_malloced_chunk (av, victim, nb);
void *p = chunk2mem (victim);
alloc_perturb (p, bytes);
return p;
#if USE_TCACHE
}
#endif
}
/* place chunk in bin */
if (in_smallbin_range (size))
{
victim_index = smallbin_index (size);
bck = bin_at (av, victim_index);
fwd = bck->fd;
}
else
{
victim_index = largebin_index (size);
bck = bin_at (av, victim_index);
fwd = bck->fd;
/* maintain large bins in sorted order */
if (fwd != bck)
{
/* Or with inuse bit to speed comparisons */
size |= PREV_INUSE;
/* if smaller than smallest, bypass loop below */
assert (chunk_main_arena (bck->bk));
if ((unsigned long) (size)
< (unsigned long) chunksize_nomask (bck->bk))
{
fwd = bck;
bck = bck->bk;
victim->fd_nextsize = fwd->fd;
victim->bk_nextsize = fwd->fd->bk_nextsize;
fwd->fd->bk_nextsize = victim->bk_nextsize->fd_nextsize = victim;
}
else
{
assert (chunk_main_arena (fwd));
while ((unsigned long) size < chunksize_nomask (fwd))
{
fwd = fwd->fd_nextsize;
assert (chunk_main_arena (fwd));
}
if ((unsigned long) size
== (unsigned long) chunksize_nomask (fwd))
/* Always insert in the second position. */
fwd = fwd->fd;
else
{
victim->fd_nextsize = fwd;
victim->bk_nextsize = fwd->bk_nextsize;
fwd->bk_nextsize = victim;
victim->bk_nextsize->fd_nextsize = victim;
}
bck = fwd->bk;
}
}
else
victim->fd_nextsize = victim->bk_nextsize = victim;
}
mark_bin (av, victim_index);
victim->bk = bck;
victim->fd = fwd;
fwd->bk = victim;
bck->fd = victim;
#if USE_TCACHE
/* If we've processed as many chunks as we're allowed while
filling the cache, return one of the cached ones. */
++tcache_unsorted_count;
if (return_cached
&& mp_.tcache_unsorted_limit > 0
&& tcache_unsorted_count > mp_.tcache_unsorted_limit)
{
return tcache_get (tc_idx);
}
#endif
#define MAX_ITERS 10000
if (++iters >= MAX_ITERS)
break;
}
#if USE_TCACHE
/* If all the small chunks we found ended up cached, return one now. */
if (return_cached)
{
return tcache_get (tc_idx);
}
#endif
/*
If a large request, scan through the chunks of current bin in
sorted order to find smallest that fits. Use the skip list for this.
*/
if (!in_smallbin_range (nb))
{
bin = bin_at (av, idx);
/* skip scan if empty or largest chunk is too small */
if ((victim = first (bin)) != bin
&& (unsigned long) chunksize_nomask (victim)
>= (unsigned long) (nb))
{
victim = victim->bk_nextsize;
while (((unsigned long) (size = chunksize (victim)) <
(unsigned long) (nb)))
victim = victim->bk_nextsize;
/* Avoid removing the first entry for a size so that the skip
list does not have to be rerouted. */
if (victim != last (bin)
&& chunksize_nomask (victim)
== chunksize_nomask (victim->fd))
victim = victim->fd;
remainder_size = size - nb;
unlink (av, victim, bck, fwd);
/* Exhaust */
if (remainder_size < MINSIZE)
{
set_inuse_bit_at_offset (victim, size);
if (av != &main_arena)
set_non_main_arena (victim);
}
/* Split */
else
{
remainder = chunk_at_offset (victim, nb);
/* We cannot assume the unsorted list is empty and therefore
have to perform a complete insert here. */
bck = unsorted_chunks (av);
fwd = bck->fd;
if (__glibc_unlikely (fwd->bk != bck))
{
errstr = "malloc(): corrupted unsorted chunks";
goto errout;
}
remainder->bk = bck;
remainder->fd = fwd;
bck->fd = remainder;
fwd->bk = remainder;
if (!in_smallbin_range (remainder_size))
{
remainder->fd_nextsize = NULL;
remainder->bk_nextsize = NULL;
}
set_head (victim, nb | PREV_INUSE |
(av != &main_arena ? NON_MAIN_ARENA : 0));
set_head (remainder, remainder_size | PREV_INUSE);
set_foot (remainder, remainder_size);
}
check_malloced_chunk (av, victim, nb);
void *p = chunk2mem (victim);
alloc_perturb (p, bytes);
return p;
}
}
/*
Search for a chunk by scanning bins, starting with next largest
bin. This search is strictly by best-fit; i.e., the smallest
(with ties going to approximately the least recently used) chunk
that fits is selected.
The bitmap avoids needing to check that most blocks are nonempty.
The particular case of skipping all bins during warm-up phases
when no chunks have been returned yet is faster than it might look.
*/
++idx;
bin = bin_at (av, idx);
block = idx2block (idx);
map = av->binmap[block];
bit = idx2bit (idx);
for (;; )
{
/* Skip rest of block if there are no more set bits in this block. */
if (bit > map || bit == 0)
{
do
{
if (++block >= BINMAPSIZE) /* out of bins */
goto use_top;
}
while ((map = av->binmap[block]) == 0);
bin = bin_at (av, (block << BINMAPSHIFT));
bit = 1;
}
/* Advance to bin with set bit. There must be one. */
while ((bit & map) == 0)
{
bin = next_bin (bin);
bit <<= 1;
assert (bit != 0);
}
/* Inspect the bin. It is likely to be non-empty */
victim = last (bin);
/* If a false alarm (empty bin), clear the bit. */
if (victim == bin)
{
av->binmap[block] = map &= ~bit; /* Write through */
bin = next_bin (bin);
bit <<= 1;
}
else
{
size = chunksize (victim);
/* We know the first chunk in this bin is big enough to use. */
assert ((unsigned long) (size) >= (unsigned long) (nb));
remainder_size = size - nb;
/* unlink */
unlink (av, victim, bck, fwd);
/* Exhaust */
if (remainder_size < MINSIZE)
{
set_inuse_bit_at_offset (victim, size);
if (av != &main_arena)
set_non_main_arena (victim);
}
/* Split */
else
{
remainder = chunk_at_offset (victim, nb);
/* We cannot assume the unsorted list is empty and therefore
have to perform a complete insert here. */
bck = unsorted_chunks (av);
fwd = bck->fd;
if (__glibc_unlikely (fwd->bk != bck))
{
errstr = "malloc(): corrupted unsorted chunks 2";
goto errout;
}
remainder->bk = bck;
remainder->fd = fwd;
bck->fd = remainder;
fwd->bk = remainder;
/* advertise as last remainder */
if (in_smallbin_range (nb))
av->last_remainder = remainder;
if (!in_smallbin_range (remainder_size))
{
remainder->fd_nextsize = NULL;
remainder->bk_nextsize = NULL;
}
set_head (victim, nb | PREV_INUSE |
(av != &main_arena ? NON_MAIN_ARENA : 0));
set_head (remainder, remainder_size | PREV_INUSE);
set_foot (remainder, remainder_size);
}
check_malloced_chunk (av, victim, nb);
void *p = chunk2mem (victim);
alloc_perturb (p, bytes);
return p;
}
}
use_top:
/*
If large enough, split off the chunk bordering the end of memory
(held in av->top). Note that this is in accord with the best-fit
search rule. In effect, av->top is treated as larger (and thus
less well fitting) than any other available chunk since it can
be extended to be as large as necessary (up to system
limitations).
We require that av->top always exists (i.e., has size >=
MINSIZE) after initialization, so if it would otherwise be
exhausted by current request, it is replenished. (The main
reason for ensuring it exists is that we may need MINSIZE space
to put in fenceposts in sysmalloc.)
*/
victim = av->top;
size = chunksize (victim);
if ((unsigned long) (size) >= (unsigned long) (nb + MINSIZE))
{
remainder_size = size - nb;
remainder = chunk_at_offset (victim, nb);
av->top = remainder;
set_head (victim, nb | PREV_INUSE |
(av != &main_arena ? NON_MAIN_ARENA : 0));
set_head (remainder, remainder_size | PREV_INUSE);
check_malloced_chunk (av, victim, nb);
void *p = chunk2mem (victim);
alloc_perturb (p, bytes);
return p;
}
/* When we are using atomic ops to free fast chunks we can get
here for all block sizes. */
else if (have_fastchunks (av))
{
malloc_consolidate (av);
/* restore original bin index */
if (in_smallbin_range (nb))
idx = smallbin_index (nb);
else
idx = largebin_index (nb);
}
/*
Otherwise, relay to handle system-dependent cases
*/
else
{
void *p = sysmalloc (nb, av);
if (p != NULL)
alloc_perturb (p, bytes);
return p;
}
}
}인자 및 변수 (추가)
변경 및 추가된 코드
- tcache와 관련된 변수 추가
더보기
#if USE_TCACHE
size_t tcache_unsorted_count; /* count of unsorted chunks processed */
#endif변수가 하나 추가 되었다 해당 변수는 tcache가 채워진 상태에서 freed chunk가 bin에 저장된 횟수를 저장한다
이후에 mp_.tcache_unsorted_limit에서 정해진 값을 넘어서면 tcache_get함수를 호출해 더이상 bins에 chunk가 쌓이는 것을 방지한다
initical check (동일)
glibc 2.23버전과 동일하다
fastbin (변경, 추가)
변경 및 추가된 코드
- fastbin을 갱신하고 최상단 청크를 가져오는 코드를 매크로로 정의해 사용
- tcache 관련 코드 추가 ( tcache를 채우는 코드 )
더보기
fastbinsY 갱신
REMOVE_FB (fb, victim, pp);fastbin을 제거하는 코드를 REMOVE_FB매크로를 정의하여 사용 (상세 내용 아래 더보기)
#define REMOVE_FB(fb, victim, pp) \
do \
{ \
victim = pp; \
if (victim == NULL) \
break; \
} \
while ((pp = catomic_compare_and_exchange_val_acq (fb, victim->fd, victim)) \
!= victim); \fastbin을 제거하는 코드가 위에서 메크로로 정의되어 사용된다
fastbin 재사용할 경우
check_remalloced_chunk이후에 tcache관련 코드가 추가 되었다
이는 tcache가 비어있고 요청한 크기의 fastbin이 존재할 경우 fastbin에 있는 freed chunk를 tcache로 옮기는 작업을 수행한다
#if USE_TCACHE
/* While we're here, if we see other chunks of the same size,
stash them in the tcache. */
size_t tc_idx = csize2tidx (nb);
if (tcache && tc_idx < mp_.tcache_bins)
{
mchunkptr tc_victim;
/* While bin not empty and tcache not full, copy chunks over. */
while (tcache->counts[tc_idx] < mp_.tcache_count
&& (pp = *fb) != NULL)
{
REMOVE_FB (fb, tc_victim, pp);
if (tc_victim != 0)
{
tcache_put (tc_victim, tc_idx);
}
}
}
#endif
해당 코드에서는 할당 요청한 크기의 bins에 저장된 fred 청크를 tcache로 옮기게 된다
- tcache_perthread_struct가 존재하고 tc_idx가 범위내에 존재하는 지 확인
- while문을 최대 7번 돌면서 fastbin에 있는 freed chunk를 뽑아와서 tcache에 저장
추가된 보안 검사
- 없음
Small bin (추가)
변경 및 추가된 코드
- tcache 관련 코드 추가 ( tcache를 채우는 코드 )
더보기
small bin reuse
check_malloced_chunk이후에 tcache 관련 코드 추가되었다
#if USE_TCACHE
/* While we're here, if we see other chunks of the same size,
stash them in the tcache. */
size_t tc_idx = csize2tidx (nb);
if (tcache && tc_idx < mp_.tcache_bins)
{
mchunkptr tc_victim;
/* While bin not empty and tcache not full, copy chunks over. */
while (tcache->counts[tc_idx] < mp_.tcache_count
&& (tc_victim = last (bin)) != bin)
{
if (tc_victim != 0)
{
bck = tc_victim->bk;
set_inuse_bit_at_offset (tc_victim, nb);
if (av != &main_arena)
set_non_main_arena (tc_victim);
bin->bk = bck;
bck->fd = bin;
tcache_put (tc_victim, tc_idx);
}
}
}2.23버전에서 check_malloced_chunk 이후에 위의 코드가 추가 되었다
- tcache_perthread_struct가 존재하고 tc_idx가 범위내에 존재하는 지 확인
- tcache->count가 7보다 작고 tc_victim에 bin->bk를 저장하고 비워져있는지 확인
- tc_victim이 NULL이 아니면 small bin에서 chunk 뽑아서 tcache에 저장
추가된 보안 검사
- 없음
large bin (동일)
glibc 2.23버전과 동일하다
using unsorted bin (추가)
변경 및 추가된 코드
- 루프가 수행되기 전에 tcache 관련 변수 추가
- unsorted bin 재할당할 때 tcache 관련 코드 추가 ( tcache를 채우는 코드 )
- while문 마지막에 tcache로 재할당하는 코드 추가 not commonly used
- while문 이후에 tcache로 재할당하는 코드 추가
더보기
before loop
#if USE_TCACHE
INTERNAL_SIZE_T tcache_nb = 0;
size_t tc_idx = csize2tidx (nb);
if (tcache && tc_idx < mp_.tcache_bins)
tcache_nb = nb;
int return_cached = 0;
tcache_unsorted_count = 0;
#endif
for (;; )
{
...루프에 들어가기 전에 tcache 관련 변수를 초기화하는 코드가 추가 되었다
- tcache_perthread_struct가 존재하고 tc_idx가 tcache_bins보다 작으면 tcache_nb를 nb로 초기화 ( 틀리면 0 )
- return cached 0으로 초기화
- tcache_unsorted_count 0으로 초기화
unsorted bin 재할당
unsorted bin을 재할당할때 NON_MAIN_ARENA비트를 설정하는 코드 뒤에 tcache관련 코드가 추가되었다
if (size == nb)
{
set_inuse_bit_at_offset (victim, size);
if (av != &main_arena)
set_non_main_arena (victim);
#if USE_TCACHE
/* Fill cache first, return to user only if cache fills.
We may return one of these chunks later. */
if (tcache_nb
&& tcache->counts[tc_idx] < mp_.tcache_count)
{
tcache_put (victim, tc_idx);
return_cached = 1;
continue;
}
else
{
#endif
check_malloced_chunk (av, victim, nb);
void *p = chunk2mem (victim);
alloc_perturb (p, bytes);
return p;
#if USE_TCACHE
}
#endif
}주석에서 말했듯이 unsored bin에 있는 freed chunk가 tcache 범위내에 존재하면 tcache를 우선적으로 채운 뒤에 재할당이 이루어진다
이때 tcache에 chunk를 채울 때 return_cached 값을 1로 설정한다
tcache 재할당 ( end of while loop )
while문의 마지막 부분에서 unsorted bin에서 tcache로 옮겨진 chunk가 존재하고 tcache_unsorted_count가 mp_.tcache_unsorted_lemit의 값을 넘겼을때 tcache_get함수를 호출하는 코드가 추가되었다
#if USE_TCACHE
/* If we've processed as many chunks as we're allowed while
filling the cache, return one of the cached ones. */
++tcache_unsorted_count;
if (return_cached
&& mp_.tcache_unsorted_limit > 0
&& tcache_unsorted_count > mp_.tcache_unsorted_limit)
{
return tcache_get (tc_idx);
}
#endif
#define MAX_ITERS 10000
if (++iters >= MAX_ITERS)
break;
}위 코드에서는 조건이 맞춰지면 tcache_get을 호출해서 tcache에 있는 freed chunk하나 반환한다
아무리 봐도 mp_.tcache_unsorted_limit은 0으로 초기화가 되어있고 이를 증가 시키거나 값을 넣는 함수를 호출하지 않는다
그리고 mp_tcache_unsorted_limit을 0으로 초기화하는 코드에서 주석을 보면 limit이 없다라고 표기되어있다
그로 인해서 위의 코드는 프로그래머가 limit을 임의로 설정하게되면 해당 limit을 넘길 경우 당 tcache를 반환하게 해서 limit을 넘기는것을 방지하도록하는 코드인 것 같다
tcache 재할당 ( after while loop )
while문 이후에 return_cached의 값이 존재하면 tcache_get함수를 호출하는 코드가 추가 되었다
#if USE_TCACHE
/* If all the small chunks we found ended up cached, return one now. */
if (return_cached)
{
return tcache_get (tc_idx);
}
#endifwhile문을 통해 unsorted bin을 모두 비운 뒤 return_cached가 양수라면 tcache_get함수를 호출한다
return_cached변수는 unsorted bin에서 할당이 가능한 청크를 tcache에 넣어줄때 1로 설정되는 변수이다
이 코드까지 왔다는 것은 tcache가 모두 채워지지 않은 채로 unsorted bin이 비워졌다는 것이므로 해당 변수가 1이면 할당 가능한 freed chunk가 tcache에 있다고 판단하여 tcache_get함수를 호출하게 된다
추가된 보안 검사
- 없음
large bin으로 재할당 (동일)
glibc 2.23버전과 동일하다
binmap 탐색을 통해 재할당 (동일)
glibc 2.23버전과 동일하다
top chunk로 재할당 (동일)
glibc 2.23버전과 동일하다
이를 제외한 코드는 2.23버전과 동일하다
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| (glibc 2.26) tcache_get (0) | 2022.05.01 |
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