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ldso, malloc: implement reclaim_gaps via __malloc_donate 

Split 'free' into unmap_chunk and bin_chunk, use the latter to introduce
__malloc_donate and use it in reclaim_gaps instead of calling 'free'.
This commit is contained in:
Alexander Monakov 2018-04-16 20:54:36 +03:00 committed by Rich Felker
parent d889cc3463
commit ce7ae11acf
2 changed files with 47 additions and 30 deletions
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16
ldso/dynlink.c
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@ -476,23 +476,15 @@ static void redo_lazy_relocs()
/* A huge hack: to make up for the wastefulness of shared libraries
* needing at least a page of dirty memory even if they have no global
* data, we reclaim the gaps at the beginning and end of writable maps
* and "donate" them to the heap by setting up minimal malloc
* structures and then freeing them. */
* and "donate" them to the heap. */
static void reclaim(struct dso *dso, size_t start, size_t end)
{
size_t *a, *z;
void __malloc_donate(char *, char *);
if (start >= dso->relro_start && start < dso->relro_end) start = dso->relro_end;
if (end >= dso->relro_start && end < dso->relro_end) end = dso->relro_start;
start = start + 6*sizeof(size_t)-1 & -4*sizeof(size_t);
end = (end & -4*sizeof(size_t)) - 2*sizeof(size_t);
if (start>end || end-start < 4*sizeof(size_t)) return;
a = laddr(dso, start);
z = laddr(dso, end);
a[-2] = 1;
a[-1] = z[0] = end-start + 2*sizeof(size_t) | 1;
z[1] = 1;
free(a);
if (start >= end) return;
__malloc_donate(laddr(dso, start), laddr(dso, end));
}
static void reclaim_gaps(struct dso *dso)

61
src/malloc/malloc.c
View File

@ -299,6 +299,8 @@ static int pretrim(struct chunk *self, size_t n, int i, int j)
return 1;
}
static void bin_chunk(struct chunk *);
static void trim(struct chunk *self, size_t n)
{
size_t n1 = CHUNK_SIZE(self);
@ -314,7 +316,7 @@ static void trim(struct chunk *self, size_t n)
next->psize = n1-n | C_INUSE;
self->csize = n | C_INUSE;
free(CHUNK_TO_MEM(split));
bin_chunk(split);
}
void *malloc(size_t n)
@ -465,29 +467,14 @@ copy_free_ret:
return new;
}
void free(void *p)
static void bin_chunk(struct chunk *self)
{
struct chunk *self, *next;
struct chunk *next = NEXT_CHUNK(self);
size_t final_size, new_size, size;
int reclaim=0;
int i;
if (!p) return;
self = MEM_TO_CHUNK(p);
if (IS_MMAPPED(self)) {
size_t extra = self->psize;
char *base = (char *)self - extra;
size_t len = CHUNK_SIZE(self) + extra;
/* Crash on double free */
if (extra & 1) a_crash();
__munmap(base, len);
return;
}
final_size = new_size = CHUNK_SIZE(self);
next = NEXT_CHUNK(self);
/* Crash on corrupted footer (likely from buffer overflow) */
if (next->psize != self->csize) a_crash();
@ -548,3 +535,41 @@ void free(void *p)
unlock_bin(i);
}
static void unmap_chunk(struct chunk *self)
{
size_t extra = self->psize;
char *base = (char *)self - extra;
size_t len = CHUNK_SIZE(self) + extra;
/* Crash on double free */
if (extra & 1) a_crash();
__munmap(base, len);
}
void free(void *p)
{
if (!p) return;
struct chunk *self = MEM_TO_CHUNK(p);
if (IS_MMAPPED(self))
unmap_chunk(self);
else
bin_chunk(self);
}
void __malloc_donate(char *start, char *end)
{
size_t align_start_up = (SIZE_ALIGN-1) & (-(uintptr_t)start - OVERHEAD);
size_t align_end_down = (SIZE_ALIGN-1) & (uintptr_t)end;
if (end - start <= OVERHEAD + align_start_up + align_end_down)
return;
start += align_start_up + OVERHEAD;
end -= align_end_down;
struct chunk *c = MEM_TO_CHUNK(start), *n = MEM_TO_CHUNK(end);
c->psize = n->csize = C_INUSE;
c->csize = n->psize = C_INUSE | (end-start);
bin_chunk(c);
}