MIPS/VxWorks targets have an unusual arrangement in that they use RELA
relocations with the o32 ABI, unlike any other MIPS target. Due to an
inconsistency in BFD however "hybrid" relocations are produced by GAS,
where despite the relocations being of the RELA type the field to be
relocated also holds an in-place addend to be applied at link time.
For example:
$ cat vxworks-rela.s
.text
foo:
la $2, bar + 0x12345678
$ mips-vxworks-as -o vxworks-rela.o vxworks-rela.s
$ mips-vxworks-objdump -dr vxworks-rela.o
vxworks-rela.o: file format elf32-bigmips-vxworks
Disassembly of section .text:
00000000 <foo>:
0: 3c021234 lui v0,0x1234
0: R_MIPS_HI16 bar+0x12345678
4: 24425678 addiu v0,v0,22136
4: R_MIPS_LO16 bar+0x12345678
$
This is due to the BFD backend being strapped for RELA relocations:
#undef elf_backend_may_use_rel_p
#define elf_backend_may_use_rel_p 0
#undef elf_backend_may_use_rela_p
#define elf_backend_may_use_rela_p 1
#undef elf_backend_default_use_rela_p
#define elf_backend_default_use_rela_p 1
but the howtos in use requesting an in-place addend, e.g.:
/* High 16 bits of symbol value. */
HOWTO (R_MIPS_HI16, /* type */
16, /* rightshift */
4, /* size */
16, /* bitsize */
false, /* pc_relative */
0, /* bitpos */
complain_overflow_dont, /* complain_on_overflow */
_bfd_mips_elf_hi16_reloc, /* special_function */
"R_MIPS_HI16", /* name */
true, /* partial_inplace */
0x0000ffff, /* src_mask */
0x0000ffff, /* dst_mask */
false), /* pcrel_offset */
/* Low 16 bits of symbol value. */
HOWTO (R_MIPS_LO16, /* type */
0, /* rightshift */
4, /* size */
16, /* bitsize */
false, /* pc_relative */
0, /* bitpos */
complain_overflow_dont, /* complain_on_overflow */
_bfd_mips_elf_lo16_reloc, /* special_function */
"R_MIPS_LO16", /* name */
true, /* partial_inplace */
0x0000ffff, /* src_mask */
0x0000ffff, /* dst_mask */
false), /* pcrel_offset */
This arrangement nevertheless happens to produce correct ELF executables
owing to the ELF linker avoiding the use of howtos and doing relocation
calculations using its own knowledge of relocation semantics embedded
directly in `mips_elf_calculate_relocation' code.
Beyond producing questionable link object files it however breaks badly
with the generic linker, such as when output is srec.
Fix the problem by providing a set of o32 RELA howtos and making VxWorks
targets use it. Complement it with a set of test cases for GAS and LD;
we expect link object files to be essentially the same as n32 ones for
other MIPS targets sans the ABI2 ELF file header flag, and machine code
produced to be the same between SREC and ELF executables.
This file contains invisible Unicode characters that are indistinguishable to humans but may be processed differently by a computer. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.
BFD is an object file library. It permits applications to use the
same routines to process object files regardless of their format.
BFD is used by the GNU debugger, assembler, linker, and the binary
utilities.
The documentation on using BFD is scanty and may be occasionally
incorrect. Pointers to documentation problems, or an entirely
rewritten manual, would be appreciated.
There is some BFD internals documentation in doc/bfdint.texi which may
help programmers who want to modify BFD.
BFD is normally built as part of another package. See the build
instructions for that package, probably in a README file in the
appropriate directory.
BFD supports the following configure options:
--target=TARGET
The default target for which to build the library. TARGET is
a configuration target triplet, such as sparc-sun-solaris.
--enable-targets=TARGET,TARGET,TARGET...
Additional targets the library should support. To include
support for all known targets, use --enable-targets=all.
--enable-64-bit-bfd
Include support for 64 bit targets. This is automatically
turned on if you explicitly request a 64 bit target, but not
for --enable-targets=all. This requires a compiler with a 64
bit integer type, such as gcc.
--enable-shared
Build BFD as a shared library.
--with-mmap
Use mmap when accessing files. This is faster on some hosts,
but slower on others. It may not work on all hosts.
Report bugs in BFD to https://sourceware.org/bugzilla/
Patches are encouraged. When sending patches, always send the output
of diff -u or diff -c from the original file to the new file. Do not
send default diff output. Do not make the diff from the new file to
the original file. Remember that any patch must not break other
systems. Remember that BFD must support cross compilation from any
host to any target, so patches which use ``#ifdef HOST'' are not
acceptable. Please also read the ``Reporting Bugs'' section of the
gcc manual.
Bug reports without patches will be remembered, but they may never get
fixed until somebody volunteers to fix them.
Copyright (C) 2012-2025 Free Software Foundation, Inc.
Copying and distribution of this file, with or without modification,
are permitted in any medium without royalty provided the copyright
notice and this notice are preserved.
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