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abd20cb637
I get the feedback recently that enable linker relaxations may fail to build some program. Consider the following case, .text foo: addi a0, a0, %pcrel_lo(.L2) call foo .L1: auipc a1, %pcrel_hi(data_g) addi a1, a1, %pcrel_lo(.L1) lui a2, %hi(data_g) addi a2, a2, %lo(data_g) lui a3, %tprel_hi(data_t) add a3, a3, tp, %tprel_add(data_t) addi a3, a3, %tprel_lo(data_t) .L2: auipc a0, %pcrel_hi(data_g) .data .word 0x0 .global data_g data_g: .word 0x1 .section .tbss data_t: .word 0x0 The current ld reports `dangerous relocation error` when doing the pcgp relaxation, test.o: in function `foo': (.text+0x0): dangerous relocation: %pcrel_lo missing matching %pcrel_hi The .L2 auipc should not be removed since it is behind the corresponding addi, so we record the information in the pcgp_relocs table to avoid removing the auipc later. But current ld still remove it since we do not update the pcgp_relocs table while doing other relaxations. I have two solutions to fix the problem, 1. Update the pcgp_relocs table once we actually delete the code. 2. Add new relax pass to do the pcgp relaxations At first I tried to do the first solution, and we need to update at least three information - hi_sec_off of riscv_pcgp_lo_reloc, hi_sec_off and hi_addr (symbol value) of riscv_pcgp_hi_reloc. Update the hi_sec_off is simple, but it is more complicate to update the symbol value, since we almost have to do parts the same works of _bfd_riscv_relax_call again in the riscv_relax_delete_bytes to get the correct symbol value. Compared with the first solution, the second one is more intuitive and simple. We add a new relax pass to do the pcgp relaxations later, so we will get all the information correctly in the _bfd_riscv_relax_call, including the symbol value, without changing so much code. I do not see any penalty by adding a new relax pass for now, so it should be fine to delay the pcgp relaxations. Besides, I have pass all riscv-gnu-toolchain regressions for this patch. bfd/ * elfnn-riscv.c (_bfd_riscv_relax_section): Add a new relax pass to do the pcgp relaxation later, after the lui and call relaxations, but before the delete and alignment relaxations. ld/ * emultempl/riscvelf.em (riscv_elf_before_allocation): Change link_info.relax_pass from 3 to 4. * testsuite/ld-riscv-elf/pcgp-relax.d: New testcase. * testsuite/ld-riscv-elf/pcgp-relax.s: Likewise. * testsuite/ld-riscv-elf/ld-riscv-elf.exp: Updated. |
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| ld.h | ||
| ld.texi | ||
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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.texi), as well as the
beginnings of an internals manual (ldint.texi).
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.texi 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) 2012-2020 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.