binutils-gdb/ld/emultempl/riscvelf.em
Nelson Chu ef9d256562 RISC-V: PR27566, Do not relax when data segment phase is exp_seg_relro_adjust.
2021-05-31  Nelson Chu  <nelson.chu@sifive.com>
            Lifang Xia  <lifang_xia@c-sky.com>

The data segment phase exp_seg_relro_adjust means we are still adjusting the
relro segments, so we will get the symbol values which havn't consider the
relro.  It is dangerous and we shouldn't do the relaxations at this stage.
Otherwise, we may get the truncated fails when the relax range crossing the
data segment.

One of the solution is that, we use a pointer to monitor the data segment
phase while relaxing, to know whether the relro has been handled or not.
Once we check the phase is exp_seg_relro_adjust, we should skip this round
of relaxations, since the incorrect symbol values will affect the correctness
of relaxations.  I think we probably need to record more information about
data segment or alignments in the future, to make sure it is safe to doing
relaxations.

For the two new testcases, relro-relax-lui and relro-relax-pcrel, we get
the following truncated errors when using toolchains, which enable relro:

(.text+0x0): relocation truncated to fit: R_RISCV_GPREL_I against symbol `SymbolRodata' defined in .rodata section in test1.o

After applying this patch, the truncated errors should be resolved.
However, only linux toolchains support -z relro, so we only test these
two testcases when supporting shared library.

bfd/
    PR 27566
    * elfnn-riscv.c (struct riscv_elf_link_hash_table): New integer pointer
    to monitor the data segment phase.
    (bfd_elfNN_riscv_set_data_segment_info): New function called by
    after_allocation, to set the data_segment_phase from expld.dataseg.
    (_bfd_riscv_relax_section): Don't relax when data_segment_phase is
    exp_seg_relro_adjust (0x4).
    * elfxx-riscv.h (bfd_elf32_riscv_set_data_segment_info): New extern.
    (bfd_elf64_riscv_set_data_segment_info): Likewise.
ld/
    PR 27566
    * emultempl/riscvelf.em (after_allocation): Call
    riscv_set_data_segment_info to set data segment phase before relaxing.
    * testsuite/ld-riscv-elf/ld-riscv-elf.exp: Updated.
    * testsuite/ld-riscv-elf/relro-relax-lui.d: New testcase.
    * testsuite/ld-riscv-elf/relro-relax-lui.s: Likewise.
    * testsuite/ld-riscv-elf/relro-relax-pcrel.d: Likewise.
    * testsuite/ld-riscv-elf/relro-relax-pcrel.s: Likewise.
2021-05-31 11:29:26 +08:00

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# This shell script emits a C file. -*- C -*-
# Copyright (C) 2004-2021 Free Software Foundation, Inc.
#
# This file is part of the GNU Binutils.
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
# MA 02110-1301, USA.
fragment <<EOF
#include "ldmain.h"
#include "ldctor.h"
#include "elf/riscv.h"
#include "elfxx-riscv.h"
static void
riscv_elf_before_allocation (void)
{
gld${EMULATION_NAME}_before_allocation ();
if (link_info.discard == discard_sec_merge)
link_info.discard = discard_l;
if (!bfd_link_relocatable (&link_info))
{
/* We always need at least some relaxation to handle code alignment. */
if (RELAXATION_DISABLED_BY_USER)
TARGET_ENABLE_RELAXATION;
else
ENABLE_RELAXATION;
}
link_info.relax_pass = 4;
}
static void
gld${EMULATION_NAME}_after_allocation (void)
{
int need_layout = 0;
/* Don't attempt to discard unused .eh_frame sections until the final link,
as we can't reliably tell if they're used until after relaxation. */
if (!bfd_link_relocatable (&link_info))
{
need_layout = bfd_elf_discard_info (link_info.output_bfd, &link_info);
if (need_layout < 0)
{
einfo (_("%X%P: .eh_frame/.stab edit: %E\n"));
return;
}
}
/* PR 27566, if the phase of data segment is exp_seg_relro_adjust,
that means we are still adjusting the relro, and shouldn't do the
relaxations at this stage. Otherwise, we will get the symbol
values beofore handling the relro, and may cause truncated fails
when the relax range crossing the data segment. One of the solution
is to monitor the data segment phase while relaxing, to know whether
the relro has been handled or not.
I think we probably need to record more information about data
segment or alignments in the future, to make sure it is safe
to doing relaxations. */
enum phase_enum *phase = &(expld.dataseg.phase);
bfd_elf${ELFSIZE}_riscv_set_data_segment_info (&link_info, (int *) phase);
do
{
ldelf_map_segments (need_layout);
}
while (bfd_elf${ELFSIZE}_riscv_restart_relax_sections (&link_info));
}
/* This is a convenient point to tell BFD about target specific flags.
After the output has been created, but before inputs are read. */
static void
riscv_create_output_section_statements (void)
{
/* See PR 22920 for an example of why this is necessary. */
if (strstr (bfd_get_target (link_info.output_bfd), "riscv") == NULL)
{
/* The RISC-V backend needs special fields in the output hash structure.
These will only be created if the output format is a RISC-V format,
hence we do not support linking and changing output formats at the
same time. Use a link followed by objcopy to change output formats. */
einfo (_("%F%P: error: cannot change output format"
" whilst linking %s binaries\n"), "RISC-V");
return;
}
}
EOF
LDEMUL_BEFORE_ALLOCATION=riscv_elf_before_allocation
LDEMUL_AFTER_ALLOCATION=gld${EMULATION_NAME}_after_allocation
LDEMUL_CREATE_OUTPUT_SECTION_STATEMENTS=riscv_create_output_section_statements