Use stable sort for ld -r relocs
Alan Modra
amodra@gmail.com
Wed Aug 26 14:03:00 GMT 2015
A number of targets emit multiple relocs at a given r_offset, and
depend on those relocs staying in their original order. qsort doesn't
satisfy this requirement, although it appears from my non-rigorous
testing that glibc's msort.c implementation may in fact be stable.
I made the mistake of backporting my PR 17666 fix to 2.25.1, thinking
the code had enough time to settle on mainline, but for anyone with a
system libc that provides an unstable qsort this will mean 2.25.1
ld -r may be broken on some targets.
PR 18867
* elflink.c (cmp_ext32l_r_offset, cmp_ext32b_r_offset): Delete.
(cmp_ext64l_r_offset, cmp_ext64b_r_offset): Delete.
(ext32l_r_offset, ext32b_r_offset, ext64l_r_offset, ext64b_r_offset):
New functions.
(elf_link_adjust_relocs): Use an insertion sort to sort relocs.
diff --git a/bfd/elflink.c b/bfd/elflink.c
index 76f6493..192ce15 100644
--- a/bfd/elflink.c
+++ b/bfd/elflink.c
@@ -8102,10 +8102,12 @@ bfd_elf_perform_complex_relocation (bfd *input_bfd,
return r;
}
-/* qsort comparison functions sorting external relocs by r_offset. */
+/* Functions to read r_offset from external (target order) reloc
+ entry. Faster than bfd_getl32 et al, because we let the compiler
+ know the value is aligned. */
-static int
-cmp_ext32l_r_offset (const void *p, const void *q)
+static bfd_vma
+ext32l_r_offset (const void *p)
{
union aligned32
{
@@ -8113,27 +8115,17 @@ cmp_ext32l_r_offset (const void *p, const void *q)
unsigned char c[4];
};
const union aligned32 *a
- = (const union aligned32 *) ((const Elf32_External_Rel *) p)->r_offset;
- const union aligned32 *b
- = (const union aligned32 *) ((const Elf32_External_Rel *) q)->r_offset;
+ = (const union aligned32 *) &((const Elf32_External_Rel *) p)->r_offset;
uint32_t aval = ( (uint32_t) a->c[0]
| (uint32_t) a->c[1] << 8
| (uint32_t) a->c[2] << 16
| (uint32_t) a->c[3] << 24);
- uint32_t bval = ( (uint32_t) b->c[0]
- | (uint32_t) b->c[1] << 8
- | (uint32_t) b->c[2] << 16
- | (uint32_t) b->c[3] << 24);
- if (aval < bval)
- return -1;
- else if (aval > bval)
- return 1;
- return 0;
+ return aval;
}
-static int
-cmp_ext32b_r_offset (const void *p, const void *q)
+static bfd_vma
+ext32b_r_offset (const void *p)
{
union aligned32
{
@@ -8141,28 +8133,18 @@ cmp_ext32b_r_offset (const void *p, const void *q)
unsigned char c[4];
};
const union aligned32 *a
- = (const union aligned32 *) ((const Elf32_External_Rel *) p)->r_offset;
- const union aligned32 *b
- = (const union aligned32 *) ((const Elf32_External_Rel *) q)->r_offset;
+ = (const union aligned32 *) &((const Elf32_External_Rel *) p)->r_offset;
uint32_t aval = ( (uint32_t) a->c[0] << 24
| (uint32_t) a->c[1] << 16
| (uint32_t) a->c[2] << 8
| (uint32_t) a->c[3]);
- uint32_t bval = ( (uint32_t) b->c[0] << 24
- | (uint32_t) b->c[1] << 16
- | (uint32_t) b->c[2] << 8
- | (uint32_t) b->c[3]);
- if (aval < bval)
- return -1;
- else if (aval > bval)
- return 1;
- return 0;
+ return aval;
}
#ifdef BFD_HOST_64_BIT
-static int
-cmp_ext64l_r_offset (const void *p, const void *q)
+static bfd_vma
+ext64l_r_offset (const void *p)
{
union aligned64
{
@@ -8170,9 +8152,7 @@ cmp_ext64l_r_offset (const void *p, const void *q)
unsigned char c[8];
};
const union aligned64 *a
- = (const union aligned64 *) ((const Elf64_External_Rel *) p)->r_offset;
- const union aligned64 *b
- = (const union aligned64 *) ((const Elf64_External_Rel *) q)->r_offset;
+ = (const union aligned64 *) &((const Elf64_External_Rel *) p)->r_offset;
uint64_t aval = ( (uint64_t) a->c[0]
| (uint64_t) a->c[1] << 8
@@ -8182,23 +8162,11 @@ cmp_ext64l_r_offset (const void *p, const void *q)
| (uint64_t) a->c[5] << 40
| (uint64_t) a->c[6] << 48
| (uint64_t) a->c[7] << 56);
- uint64_t bval = ( (uint64_t) b->c[0]
- | (uint64_t) b->c[1] << 8
- | (uint64_t) b->c[2] << 16
- | (uint64_t) b->c[3] << 24
- | (uint64_t) b->c[4] << 32
- | (uint64_t) b->c[5] << 40
- | (uint64_t) b->c[6] << 48
- | (uint64_t) b->c[7] << 56);
- if (aval < bval)
- return -1;
- else if (aval > bval)
- return 1;
- return 0;
+ return aval;
}
-static int
-cmp_ext64b_r_offset (const void *p, const void *q)
+static bfd_vma
+ext64b_r_offset (const void *p)
{
union aligned64
{
@@ -8206,9 +8174,7 @@ cmp_ext64b_r_offset (const void *p, const void *q)
unsigned char c[8];
};
const union aligned64 *a
- = (const union aligned64 *) ((const Elf64_External_Rel *) p)->r_offset;
- const union aligned64 *b
- = (const union aligned64 *) ((const Elf64_External_Rel *) q)->r_offset;
+ = (const union aligned64 *) &((const Elf64_External_Rel *) p)->r_offset;
uint64_t aval = ( (uint64_t) a->c[0] << 56
| (uint64_t) a->c[1] << 48
@@ -8218,19 +8184,7 @@ cmp_ext64b_r_offset (const void *p, const void *q)
| (uint64_t) a->c[5] << 16
| (uint64_t) a->c[6] << 8
| (uint64_t) a->c[7]);
- uint64_t bval = ( (uint64_t) b->c[0] << 56
- | (uint64_t) b->c[1] << 48
- | (uint64_t) b->c[2] << 40
- | (uint64_t) b->c[3] << 32
- | (uint64_t) b->c[4] << 24
- | (uint64_t) b->c[5] << 16
- | (uint64_t) b->c[6] << 8
- | (uint64_t) b->c[7]);
- if (aval < bval)
- return -1;
- else if (aval > bval)
- return 1;
- return 0;
+ return aval;
}
#endif
@@ -8299,16 +8253,20 @@ elf_link_adjust_relocs (bfd *abfd,
(*swap_out) (abfd, irela, erela);
}
- if (sort)
+ if (sort && count != 0)
{
- int (*compare) (const void *, const void *);
+ bfd_vma (*ext_r_off) (const void *);
+ bfd_vma r_off;
+ size_t elt_size;
+ bfd_byte *base, *end, *p, *loc;
+ bfd_byte buf[sizeof (Elf64_External_Rela)];
if (bed->s->arch_size == 32)
{
if (abfd->xvec->header_byteorder == BFD_ENDIAN_LITTLE)
- compare = cmp_ext32l_r_offset;
+ ext_r_off = ext32l_r_offset;
else if (abfd->xvec->header_byteorder == BFD_ENDIAN_BIG)
- compare = cmp_ext32b_r_offset;
+ ext_r_off = ext32b_r_offset;
else
abort ();
}
@@ -8316,14 +8274,61 @@ elf_link_adjust_relocs (bfd *abfd,
{
#ifdef BFD_HOST_64_BIT
if (abfd->xvec->header_byteorder == BFD_ENDIAN_LITTLE)
- compare = cmp_ext64l_r_offset;
+ ext_r_off = ext64l_r_offset;
else if (abfd->xvec->header_byteorder == BFD_ENDIAN_BIG)
- compare = cmp_ext64b_r_offset;
+ ext_r_off = ext64b_r_offset;
else
#endif
abort ();
}
- qsort (reldata->hdr->contents, count, reldata->hdr->sh_entsize, compare);
+
+ /* Must use a stable sort here. Insertion sort, since the
+ relocs are mostly sorted already. */
+ elt_size = reldata->hdr->sh_entsize;
+ base = reldata->hdr->contents;
+ end = base + count * elt_size;
+ if (elt_size > sizeof (buf))
+ abort ();
+
+ /* Ensure the first element is lowest. This acts as a sentinel,
+ speeding the main loop below. */
+ r_off = (*ext_r_off) (base);
+ for (p = loc = base; (p += elt_size) < end; )
+ {
+ bfd_vma r_off2 = (*ext_r_off) (p);
+ if (r_off > r_off2)
+ {
+ r_off = r_off2;
+ loc = p;
+ }
+ }
+ if (loc != base)
+ {
+ /* Don't just swap *base and *loc as that changes the order
+ of the original base[0] and base[1] if they happen to
+ have the same r_offset. */
+ memcpy (buf, loc, elt_size);
+ memmove (base + elt_size, base, loc - base);
+ memcpy (base, buf, elt_size);
+ }
+
+ for (p = base + elt_size; (p += elt_size) < end; )
+ {
+ /* base to p is sorted, *p is next to insert. */
+ r_off = (*ext_r_off) (p);
+ /* Search the sorted region for location to insert. */
+ loc = p - elt_size;
+ while (r_off < (*ext_r_off) (loc))
+ loc -= elt_size;
+ loc += elt_size;
+ if (loc != p)
+ {
+ memcpy (buf, p, elt_size);
+ memmove (loc + elt_size, loc, p - loc);
+ memcpy (loc, buf, elt_size);
+ }
+ }
+ /* Hashes are no longer valid. */
free (reldata->hashes);
reldata->hashes = NULL;
}
--
Alan Modra
Australia Development Lab, IBM
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