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0c11728627
Fix a generic BFD issue with relocations against absolute symbols, which are installed without using any individual relocation handler provided by the backend. This causes any absolute section's addend to be lost on REL targets such as o32 MIPS, and also relocation-specific calculation adjustments are not made. As an example assembling this program: $ cat test.s .text foo: b bar b baz .set bar, 0x1234 $ as -EB -32 -o test-o32.o test.s $ as -EB -n32 -o test-n32.o test.s produces this binary code: $ objdump -dr test-o32.o test-n32.o test-o32.o: file format elf32-tradbigmips Disassembly of section .text: 00000000 <foo>: 0: 10000000 b 4 <foo+0x4> 0: R_MIPS_PC16 *ABS* 4: 00000000 nop 8: 1000ffff b 8 <foo+0x8> 8: R_MIPS_PC16 baz c: 00000000 nop test-n32.o: file format elf32-ntradbigmips Disassembly of section .text: 00000000 <foo>: 0: 10000000 b 4 <foo+0x4> 0: R_MIPS_PC16 *ABS*+0x1230 4: 00000000 nop 8: 10000000 b c <foo+0xc> 8: R_MIPS_PC16 baz-0x4 c: 00000000 nop $ where it is clearly visible in `test-o32.o', which uses REL relocations, that the absolute section's addend equivalent to the value of `bar' -- a reference to which cannot be fully resolved at the assembly time, because the reference is PC-relative -- has been lost, as has been the relocation-specific adjustment of -4, required to take into account the PC+4-relative calculation made by hardware with branches and seen in the external symbol reference to `baz' as the `ffff' addend encoded in the instruction word. In `test-n32.o', which uses RELA relocations, the absolute section's addend has been correctly retained. Give precedence then in `bfd_perform_relocation' and `bfd_install_relocation' to any individual relocation handler the backend selected may have provided, while still resorting to the generic calculation otherwise. This retains the semantics which we've had since forever or before the beginning of our repository history, and is at the very least compatible with `bfd_elf_generic_reloc' being used as the handler. Retain the `bfd_is_und_section' check unchanged at the beginning of `bfd_perform_relocation' since this does not affect the semantics of the function. The check returns the same `bfd_reloc_undefined' code the check for a null `howto' does, so swapping the two does not matter. Also the check is is mutually exclusive with the `bfd_is_abs_section' check, since a section cannot be absolute and undefined both at once, so swapping the two does not matter either. With this change applied the program quoted above now has the in-place addend correctly calculated and installed in the field being relocated: $ objdump -dr fixed-o32.o fixed-o32.o: file format elf32-tradbigmips Disassembly of section .text: 00000000 <foo>: 0: 1000048c b 1234 <bar> 0: R_MIPS_PC16 *ABS* 4: 00000000 nop 8: 1000ffff b 8 <foo+0x8> 8: R_MIPS_PC16 baz c: 00000000 nop $ Add a set of MIPS tests to cover the relevant cases, including absolute symbols with addends, and verifying that PC-relative relocations against symbols concerned resolve to the same value in the final link regardless of whether the REL or the RELA relocation form is used. Exclude linker tests though which would overflow the in-place addend on REL targets and use them as dump patterns for RELA targets only. bfd/ * reloc.c (bfd_perform_relocation): Try the `howto' handler first with relocations against absolute symbols. (bfd_install_relocation): Likewise. gas/ * testsuite/gas/mips/mips16-branch-absolute.d: Update patterns. * testsuite/gas/mips/branch-absolute.d: New test. * testsuite/gas/mips/branch-absolute-n32.d: New test. * testsuite/gas/mips/branch-absolute-n64.d: New test. * testsuite/gas/mips/branch-absolute-addend-n32.d: New test. * testsuite/gas/mips/branch-absolute-addend-n64.d: New test. * testsuite/gas/mips/mips16-branch-absolute-n32.d: New test. * testsuite/gas/mips/mips16-branch-absolute-n64.d: New test. * testsuite/gas/mips/mips16-branch-absolute-addend-n32.d: New test. * testsuite/gas/mips/mips16-branch-absolute-addend-n64.d: New test. * testsuite/gas/mips/micromips-branch-absolute.d: New test. * testsuite/gas/mips/micromips-branch-absolute-n32.d: New test. * testsuite/gas/mips/micromips-branch-absolute-n64.d: New test. * testsuite/gas/mips/micromips-branch-absolute-addend-n32.d: New test. * testsuite/gas/mips/micromips-branch-absolute-addend-n64.d: New test. * testsuite/gas/mips/branch-absolute.s: New test source. * testsuite/gas/mips/branch-absolute-addend.s: New test source. * testsuite/gas/mips/mips16-branch-absolute-addend.s: New test source. * testsuite/gas/mips/micromips-branch-absolute.s: New test source. * testsuite/gas/mips/micromips-branch-absolute-addend.s: New test source. * testsuite/gas/mips/mips.exp: Run the new tests. ld/ * testsuite/ld-mips-elf/branch-absolute.d: New test. * testsuite/ld-mips-elf/branch-absolute-n32.d: New test. * testsuite/ld-mips-elf/branch-absolute-n64.d: New test. * testsuite/ld-mips-elf/branch-absolute-addend.d: New test. * testsuite/ld-mips-elf/branch-absolute-addend-n32.d: New test. * testsuite/ld-mips-elf/branch-absolute-addend-n64.d: New test. * testsuite/ld-mips-elf/micromips-branch-absolute.d: New test. * testsuite/ld-mips-elf/micromips-branch-absolute-n32.d: New test. * testsuite/ld-mips-elf/micromips-branch-absolute-n64.d: New test. * testsuite/ld-mips-elf/micromips-branch-absolute-addend.d: New test. * testsuite/ld-mips-elf/micromips-branch-absolute-addend-n32.d: New test. * testsuite/ld-mips-elf/micromips-branch-absolute-addend-n64.d: New test. * testsuite/ld-mips-elf/mips-elf.exp: Run the new tests, except from `branch-absolute-addend' and `micromips-branch-absolute-addend', referred indirectly only. |
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| .. | ||
| emulparams | ||
| emultempl | ||
| po | ||
| scripttempl | ||
| testsuite | ||
| .gitignore | ||
| aclocal.m4 | ||
| ChangeLog | ||
| ChangeLog-0001 | ||
| ChangeLog-0203 | ||
| ChangeLog-2004 | ||
| ChangeLog-2005 | ||
| ChangeLog-2006 | ||
| ChangeLog-2007 | ||
| ChangeLog-2008 | ||
| ChangeLog-2009 | ||
| ChangeLog-2010 | ||
| ChangeLog-2011 | ||
| ChangeLog-2012 | ||
| ChangeLog-2013 | ||
| ChangeLog-2014 | ||
| ChangeLog-2015 | ||
| ChangeLog-9197 | ||
| ChangeLog-9899 | ||
| config.in | ||
| configure | ||
| configure.ac | ||
| configure.host | ||
| configure.tgt | ||
| deffile.h | ||
| deffilep.y | ||
| dep-in.sed | ||
| elf-hints-local.h | ||
| fdl.texi | ||
| gen-doc.texi | ||
| genscrba.sh | ||
| genscripts.sh | ||
| h8-doc.texi | ||
| ld.h | ||
| ld.texinfo | ||
| ldbuildid.c | ||
| ldbuildid.h | ||
| ldcref.c | ||
| ldctor.c | ||
| ldctor.h | ||
| ldemul.c | ||
| ldemul.h | ||
| ldexp.c | ||
| ldexp.h | ||
| ldfile.c | ||
| ldfile.h | ||
| ldgram.y | ||
| ldint.texinfo | ||
| ldlang.c | ||
| ldlang.h | ||
| ldlex-wrapper.c | ||
| ldlex.h | ||
| ldlex.l | ||
| ldmain.c | ||
| ldmain.h | ||
| ldmisc.c | ||
| ldmisc.h | ||
| ldver.c | ||
| ldver.h | ||
| ldwrite.c | ||
| ldwrite.h | ||
| lexsup.c | ||
| MAINTAINERS | ||
| Makefile.am | ||
| Makefile.in | ||
| mri.c | ||
| mri.h | ||
| NEWS | ||
| pe-dll.c | ||
| pe-dll.h | ||
| pep-dll.c | ||
| pep-dll.h | ||
| plugin.c | ||
| plugin.h | ||
| README | ||
| stamp-h.in | ||
| sysdep.h | ||
| testplug2.c | ||
| testplug3.c | ||
| testplug4.c | ||
| testplug.c | ||
| TODO | ||
README for LD
This is the GNU linker. It is distributed with other "binary
utilities" which should be in ../binutils. See ../binutils/README for
more general notes, including where to send bug reports.
There are many features of the linker:
* The linker uses a Binary File Descriptor library (../bfd)
that it uses to read and write object files. This helps
insulate the linker itself from the format of object files.
* The linker supports a number of different object file
formats. It can even handle multiple formats at once:
Read two input formats and write a third.
* The linker can be configured for cross-linking.
* The linker supports a control language.
* There is a user manual (ld.texinfo), as well as the
beginnings of an internals manual (ldint.texinfo).
Installation
============
See ../binutils/README.
If you want to make a cross-linker, you may want to specify
a different search path of -lfoo libraries than the default.
You can do this by setting the LIB_PATH variable in ./Makefile
or using the --with-lib-path configure switch.
To build just the linker, make the target all-ld from the top level
directory (one directory above this one).
Porting to a new target
=======================
See the ldint.texinfo manual.
Reporting bugs etc
===========================
See ../binutils/README.
Known problems
==============
The Solaris linker normally exports all dynamic symbols from an
executable. The GNU linker does not do this by default. This is
because the GNU linker tries to present the same interface for all
similar targets (in this case, all native ELF targets). This does not
matter for normal programs, but it can make a difference for programs
which try to dlopen an executable, such as PERL or Tcl. You can make
the GNU linker export all dynamic symbols with the -E or
--export-dynamic command line option.
HP/UX 9.01 has a shell bug that causes the linker scripts to be
generated incorrectly. The symptom of this appears to be "fatal error
- scanner input buffer overflow" error messages. There are various
workarounds to this:
* Build and install bash, and build with "make SHELL=bash".
* Update to a version of HP/UX with a working shell (e.g., 9.05).
* Replace "(. ${srcdir}/scripttempl/${SCRIPT_NAME}.sc)" in
genscripts.sh with "sh ${srcdir}..." (no parens) and make sure the
emulparams script used exports any shell variables it sets.
Copyright (C) 2012-2016 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.