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work around incorrect EPERM from mmap syscall

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under some conditions, the mmap syscall wrongly fails with EPERM
instead of ENOMEM when memory is exhausted; this is probably the
result of the kernel trying to fit the allocation somewhere that
crosses into the kernel range or below mmap_min_addr. in any case it's
a conformance bug, so work around it. for now, only handle the case of
anonymous mappings with no requested address; in other cases EPERM may
be a legitimate error.

this indirectly fixes the possibility of malloc failing with the wrong
errno value.
This commit is contained in:
Rich Felker 2017-09-06 22:09:28 -04:00
parent 8c4be3e220
commit da438ee1fc
1 changed files with 7 additions and 2 deletions
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9
src/mman/mmap.c
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@ -14,6 +14,7 @@ weak_alias(dummy, __vm_wait);
void *__mmap(void *start, size_t len, int prot, int flags, int fd, off_t off) void *__mmap(void *start, size_t len, int prot, int flags, int fd, off_t off)
{ {
long ret;
if (off & OFF_MASK) { if (off & OFF_MASK) {
errno = EINVAL; errno = EINVAL;
return MAP_FAILED; return MAP_FAILED;
@ -26,10 +27,14 @@ void *__mmap(void *start, size_t len, int prot, int flags, int fd, off_t off)
__vm_wait(); __vm_wait();
} }
#ifdef SYS_mmap2 #ifdef SYS_mmap2
return (void *)syscall(SYS_mmap2, start, len, prot, flags, fd, off/UNIT); ret = __syscall(SYS_mmap2, start, len, prot, flags, fd, off/UNIT);
#else #else
return (void *)syscall(SYS_mmap, start, len, prot, flags, fd, off); ret = __syscall(SYS_mmap, start, len, prot, flags, fd, off);
#endif #endif
/* Fixup incorrect EPERM from kernel. */
if (ret == -EPERM && !start && (flags&MAP_ANON) && !(flags&MAP_FIXED))
ret = -ENOMEM;
return (void *)__syscall_ret(ret);
} }
weak_alias(__mmap, mmap); weak_alias(__mmap, mmap);