RepoMirrors/musl
1
0
Fork 0
mirror of git://git.musl-libc.org/musl synced 2025-01-18 12:50:58 +00:00
Code Issues Packages Projects Releases Wiki Activity

reclaim the memory wasted by dynamic linking for use by malloc

Browse Source
This commit is contained in:
Rich Felker 2011-06-28 19:40:14 -04:00
parent e411827960
commit 6717e62ac0
1 changed files with 39 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

39
src/ldso/dynlink.c
View File

@ -139,6 +139,37 @@ static void do_relocs(unsigned char *base, size_t *rel, size_t rel_size, size_t
}
}
/* 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. */
static void reclaim(unsigned char *base, size_t start, size_t end)
{
size_t *a, *z;
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 = (size_t *)(base + start);
z = (size_t *)(base + end);
a[-2] = 1;
a[-1] = z[0] = end-start + 2*sizeof(size_t) | 1;
z[1] = 1;
free(a);
}
static void reclaim_gaps(unsigned char *base, Phdr *ph, size_t phent, size_t phcnt)
{
for (; phcnt--; ph=(void *)((char *)ph+phent)) {
if (ph->p_type!=PT_LOAD) continue;
if ((ph->p_flags&(PF_R|PF_W))!=(PF_R|PF_W)) continue;
reclaim(base, ph->p_vaddr & -PAGE_SIZE, ph->p_vaddr);
reclaim(base, ph->p_vaddr+ph->p_memsz,
ph->p_vaddr+ph->p_memsz+PAGE_SIZE-1 & -PAGE_SIZE);
}
}
static void *map_library(int fd, size_t *lenp, unsigned char **basep, size_t *dynp)
{
Ehdr buf[(896+sizeof(Ehdr))/sizeof(Ehdr)];
@ -217,6 +248,8 @@ static void *map_library(int fd, size_t *lenp, unsigned char **basep, size_t *dy
}
}
}
if (!runtime) reclaim_gaps(base, (void *)((char *)buf + eh->e_phoff),
eh->e_phentsize, eh->e_phnum);
*lenp = map_len;
*basep = base;
*dynp = dyn;
@ -398,6 +431,7 @@ void *__dynlink(int argc, char **argv, size_t *got)
size_t lib_dyn[DYN_CNT] = {0};
size_t i;
Phdr *phdr;
Ehdr *ehdr;
struct dso lib, app;
/* Find aux vector just past environ[] */
@ -456,6 +490,11 @@ void *__dynlink(int argc, char **argv, size_t *got)
/* At this point the standard library is fully functional */
reclaim_gaps(app.base, (void *)aux[AT_PHDR], aux[AT_PHENT], aux[AT_PHNUM]);
ehdr = (void *)lib.base;
reclaim_gaps(lib.base, (void *)(lib.base+ehdr->e_phoff),
ehdr->e_phentsize, ehdr->e_phnum);
head = tail = &app;
libc = &lib;
app.next = 0;