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preserve errno across free

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as an outcome of Austin Group issue #385, future versions of the
standard will require free not to alter the value of errno. save and
restore it individually around the calls to madvise and munmap so that
the cost is not imposed on calls to free that do not result in any
syscall.
This commit is contained in:
Rich Felker 2021-01-30 17:14:20 -05:00
parent 9afed99c22
commit 2010df0d64
1 changed files with 10 additions and 2 deletions
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12
src/malloc/mallocng/free.c
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@ -119,7 +119,11 @@ void free(void *p)
if (((uintptr_t)(start-1) ^ (uintptr_t)end) >= 2*PGSZ && g->last_idx) {
unsigned char *base = start + (-(uintptr_t)start & (PGSZ-1));
size_t len = (end-base) & -PGSZ;
if (len) madvise(base, len, MADV_FREE);
if (len) {
int e = errno;
madvise(base, len, MADV_FREE);
errno = e;
}
}
// atomic free without locking if this is neither first or last slot
@ -139,5 +143,9 @@ void free(void *p)
wrlock();
struct mapinfo mi = nontrivial_free(g, idx);
unlock();
if (mi.len) munmap(mi.base, mi.len);
if (mi.len) {
int e = errno;
munmap(mi.base, mi.len);
errno = e;
}
}