[Patch bfd/mach-o] some tweaks to bfd_mach_o_canonicalize_one_reloc
Iain Sandoe
developer@sandoe-acoustics.co.uk
Wed Feb 22 16:35:00 GMT 2012
I tried looking at a ppc object with objdump, and got a seg-fault -
which was eventually traced to an icky situation that we need to swap
the bit-fields in non-scattered relocs. This is (kinda) documented in
the system /usr/include/mach-o/reloc.h (it's documented by the absence
of an endian-dependent version of the non-scattered reloc, where the
comments indicate that such is needed for the scattered one).
This testing also revealed that the PAIR does not have to be scattered
(and that the sym value needs to be found differently for such).
[that's what this patch fixes - at least for the input side]
---- NOTE:
There is also a lurking problem (not fixed by this patch, but FIXME'd)
that reloc symbols that appear right at the end of the section data e.g.
.text
Lstart:
some stuff
Lend:
.a_different_section ...
Lend would (if emitted as part of a reloc) end up associated with
"a_different_section" or nul if "a_different_section" required some
alignment padding. IIRC, the vendor's tool-chain used to have this
problem... I think we'll need to fix it by doing the canonicalize
operations per section, but not looked hard yet.
----
so patch to fix endian-ness of bit-fields in
bfd_mach_o_canonicalize_one_reloc non-scattered
OK?
Iain
include:
* mach-o/external.h (bfd_mach_o_reg_reloc_swap): New typedef.
bfd:
* mach-o.c (swap_relocs): New var.
(bfd_mach_o_canonicalize_one_reloc): Swap non-scattered reloc
bit-fields when target and host differ in endian-ness. When
PAIRs are non-scattered find the 'symbol' from the preceding
reloc. Add FIXME re. reloc symbols on section boundaries.
bfd/mach-o.c | 58 ++++++++++++++++++++++++++++++++++
+---------
include/mach-o/external.h | 27 +++++++++++++++++++++
2 files changed, 73 insertions(+), 12 deletions(-)
diff --git a/bfd/mach-o.c b/bfd/mach-o.c
index ff84de0..4e86cc9 100644
--- a/bfd/mach-o.c
+++ b/bfd/mach-o.c
@@ -975,6 +975,8 @@ bfd_mach_o_get_reloc_upper_bound (bfd *abfd
ATTRIBUTE_UNUSED,
return (asect->reloc_count + 1) * sizeof (arelent *);
}
+static bfd_boolean swap_relocs = FALSE;
+
static int
bfd_mach_o_canonicalize_one_reloc (bfd *abfd,
struct mach_o_reloc_info_external
*raw,
@@ -998,6 +1000,11 @@ bfd_mach_o_canonicalize_one_reloc (bfd *abfd,
Extract section and offset from r_value. */
res->sym_ptr_ptr = NULL;
res->addend = 0;
+ /* FIXME: This breaks when a symbol in a reloc exactly follows
the
+ end of the data for the section (e.g. in a calculation of section
+ data length). At present, the symbol will end up associated with
+ the following section or, if it falls within alignment padding, as
+ null - which will assert later. */
for (j = 0; j < mdata->nsects; j++)
{
bfd_mach_o_section *sect = mdata->sections[j];
@@ -1016,32 +1023,55 @@ bfd_mach_o_canonicalize_one_reloc (bfd *abfd,
}
else
{
- unsigned int num = BFD_MACH_O_GET_R_SYMBOLNUM (symnum);
+ bfd_mach_o_reg_reloc_swap s;
+ unsigned int num;
+
res->addend = 0;
res->address = addr;
- if (symnum & BFD_MACH_O_R_EXTERN)
- {
- sym = syms + num;
- reloc.r_extern = 1;
- }
+ reloc.r_scattered = 0;
+ /* For the 'regular' reloc we need to account for the endian-
ness of
+ the bitfields. */
+ s.access = symnum;
+ if (swap_relocs)
+ {
+ reloc.r_type = s.rev.r_type;
+ reloc.r_extern = s.rev.r_extern;
+ reloc.r_length = s.rev.r_length;
+ reloc.r_pcrel = s.rev.r_pcrel;
+ num = s.rev.r_symbolnum;
+ }
else
+ {
+ num = s.fwd.r_symbolnum;
+ reloc.r_pcrel = s.fwd.r_pcrel;
+ reloc.r_length = s.fwd.r_length;
+ reloc.r_extern = s.fwd.r_extern;
+ reloc.r_type = s.fwd.r_type;
+ }
+
+ if (reloc.r_extern)
+ sym = syms + num;
+ else if (reloc.r_scattered
+ || (reloc.r_type != BFD_MACH_O_GENERIC_RELOC_PAIR))
{
BFD_ASSERT (num != 0);
BFD_ASSERT (num <= mdata->nsects);
sym = mdata->sections[num - 1]->bfdsection->symbol_ptr_ptr;
/* For a symbol defined in section S, the addend (stored
in the
binary) contains the address of the section. To comply
with
- bfd conventio, substract the section address.
+ bfd convention, subtract the section address.
Use the address from the header, so that the user can
modify
the vma of the section. */
res->addend = -mdata->sections[num - 1]->addr;
- reloc.r_extern = 0;
+ }
+ else /* the symnum appears to be 0x00ffffff ('-1' 24 bits) . */
+ {
+ /* Pairs for PPC LO/HI/HA are not scattered, but contain
the offset
+ in the lower 16bits of the address value. So we have to
find the
+ 'symbol' from the preceding reloc. */
+ sym = (res-1)->sym_ptr_ptr;
}
res->sym_ptr_ptr = sym;
- reloc.r_type = BFD_MACH_O_GET_R_TYPE (symnum);
- reloc.r_length = BFD_MACH_O_GET_R_LENGTH (symnum);
- reloc.r_pcrel = (symnum & BFD_MACH_O_R_PCREL) ? 1 : 0;
- reloc.r_scattered = 0;
}
if (!(*bed->_bfd_mach_o_swap_reloc_in)(res, &reloc))
@@ -1058,6 +1088,10 @@ bfd_mach_o_canonicalize_relocs (bfd *abfd,
unsigned long filepos,
struct mach_o_reloc_info_external *native_relocs;
bfd_size_type native_size;
+ i = 1;
+ if (bfd_get_32 (abfd, &i) != 1)
+ swap_relocs = TRUE;
+
/* Allocate and read relocs. */
native_size = count * BFD_MACH_O_RELENT_SIZE;
native_relocs =
diff --git a/include/mach-o/external.h b/include/mach-o/external.h
index ad419ef..2396073 100644
--- a/include/mach-o/external.h
+++ b/include/mach-o/external.h
@@ -284,4 +284,31 @@ struct mach_o_fat_arch_external
unsigned char align[4]; /* Power of 2. */
};
+/* For non-scattered relocations, we have to account for the bit-
endianess
+ of the fields within the reloc. So these need to be swapped in/
out when
+ the endianess of the host differs from the target. */
+
+typedef union bfd_mach_o_reg_reloc_swap
+{
+ unsigned int access;
+ struct
+ {
+ unsigned int r_symbolnum:24,
+ r_pcrel:1,
+ r_length:2,
+ r_extern:1,
+ r_type:4;
+ } fwd;
+ struct
+ {
+ unsigned int r_type:4,
+ r_extern:1,
+ r_length:2,
+ r_pcrel:1,
+ r_symbolnum:24;
+ } rev;
+}
+bfd_mach_o_reg_reloc_swap;
+
+
#endif /* _MACH_O_EXTERNAL_H */
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