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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.
92 lines
2.8 KiB
Plaintext
92 lines
2.8 KiB
Plaintext
# This shell script emits a C file. -*- C -*-
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# Copyright (C) 2004-2020 Free Software Foundation, Inc.
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#
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# This file is part of the GNU Binutils.
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
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# MA 02110-1301, USA.
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fragment <<EOF
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#include "ldmain.h"
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#include "ldctor.h"
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#include "elf/riscv.h"
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#include "elfxx-riscv.h"
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static void
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riscv_elf_before_allocation (void)
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{
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gld${EMULATION_NAME}_before_allocation ();
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if (link_info.discard == discard_sec_merge)
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link_info.discard = discard_l;
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if (!bfd_link_relocatable (&link_info))
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{
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/* We always need at least some relaxation to handle code alignment. */
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if (RELAXATION_DISABLED_BY_USER)
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TARGET_ENABLE_RELAXATION;
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else
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ENABLE_RELAXATION;
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}
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link_info.relax_pass = 4;
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}
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static void
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gld${EMULATION_NAME}_after_allocation (void)
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{
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int need_layout = 0;
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/* Don't attempt to discard unused .eh_frame sections until the final link,
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as we can't reliably tell if they're used until after relaxation. */
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if (!bfd_link_relocatable (&link_info))
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{
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need_layout = bfd_elf_discard_info (link_info.output_bfd, &link_info);
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if (need_layout < 0)
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{
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einfo (_("%X%P: .eh_frame/.stab edit: %E\n"));
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return;
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}
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}
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ldelf_map_segments (need_layout);
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}
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/* This is a convenient point to tell BFD about target specific flags.
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After the output has been created, but before inputs are read. */
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static void
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riscv_create_output_section_statements (void)
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{
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/* See PR 22920 for an example of why this is necessary. */
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if (strstr (bfd_get_target (link_info.output_bfd), "riscv") == NULL)
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{
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/* The RISC-V backend needs special fields in the output hash structure.
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These will only be created if the output format is a RISC-V format,
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hence we do not support linking and changing output formats at the
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same time. Use a link followed by objcopy to change output formats. */
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einfo (_("%F%P: error: cannot change output format"
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" whilst linking %s binaries\n"), "RISC-V");
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return;
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}
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}
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EOF
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LDEMUL_BEFORE_ALLOCATION=riscv_elf_before_allocation
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LDEMUL_AFTER_ALLOCATION=gld${EMULATION_NAME}_after_allocation
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LDEMUL_CREATE_OUTPUT_SECTION_STATEMENTS=riscv_create_output_section_statements
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