[PATCH] LoongArch:ld: Fix relocation error of pcrel.

[liuzhensong]

在 2022/9/3 下午12:33, Fangrui Song 写道:
> On Fri, Sep 2, 2022 at 6:29 PM liuzhensong <liuzhensong@loongson.cn> wrote:
>>    Patch for branch 2.39.
>>    Need to reduce the address of pc when using
>>    reloction R_LARCH_SOP_PUSH_PLT_PCREL.
>>
>>    bfd/
>>      * elfnn-loongarch.c
>> ---
>>   bfd/elfnn-loongarch.c                         |  3 +-
>>   ld/testsuite/ld-loongarch-elf/pcrel-const.d   | 14 +++++++
>>   ld/testsuite/ld-loongarch-elf/pcrel-const.lds | 14 +++++++
>>   ld/testsuite/ld-loongarch-elf/pcrel-const.s   | 11 ++++++
>>   ld/testsuite/ld-loongarch-elf/pr.exp          | 39 +++++++++++++++++++
>>   5 files changed, 80 insertions(+), 1 deletion(-)
>>   create mode 100644 ld/testsuite/ld-loongarch-elf/pcrel-const.d
>>   create mode 100644 ld/testsuite/ld-loongarch-elf/pcrel-const.lds
>>   create mode 100644 ld/testsuite/ld-loongarch-elf/pcrel-const.s
>>   create mode 100644 ld/testsuite/ld-loongarch-elf/pr.exp
>>
>> diff --git a/bfd/elfnn-loongarch.c b/bfd/elfnn-loongarch.c
>> index 5b44901b9e0..fafdc7c7458 100644
>> --- a/bfd/elfnn-loongarch.c
>> +++ b/bfd/elfnn-loongarch.c
>> @@ -2341,9 +2341,10 @@ loongarch_elf_relocate_section (bfd *output_bfd, struct bfd_link_info *info,
>>          case R_LARCH_SOP_PUSH_PLT_PCREL:
>>            unresolved_reloc = false;
>>
>> -         if (resolved_to_const)
>> +         if (!is_undefweak && resolved_to_const)
>>              {
>>                relocation += rel->r_addend;
>> +             relocation -= pc;
>>                break;
>>              }
>>            else if (is_undefweak)
>> diff --git a/ld/testsuite/ld-loongarch-elf/pcrel-const.d b/ld/testsuite/ld-loongarch-elf/pcrel-const.d
>> new file mode 100644
>> index 00000000000..72abb204122
>> --- /dev/null
>> +++ b/ld/testsuite/ld-loongarch-elf/pcrel-const.d
>> @@ -0,0 +1,14 @@
>> +#as: -mla-global-with-pcrel
>> +#objdump: -Drsz
>> +
>> +.*:[    ]+file format .*
>> +
>> +
>> +Disassembly of section .text:
>> +
>> +.* <foo>:
>> +#...
>> +[      ]+4:[   ]+02c03084[     ]+addi.d[       ]+\$a0,[        ]+\$a0,[        ]+12\(0xc\)
>> +#...
>> +0+10 <__sec_end>:
>> +#pass
>> diff --git a/ld/testsuite/ld-loongarch-elf/pcrel-const.lds b/ld/testsuite/ld-loongarch-elf/pcrel-const.lds
>> new file mode 100644
>> index 00000000000..064a6894b4d
>> --- /dev/null
>> +++ b/ld/testsuite/ld-loongarch-elf/pcrel-const.lds
>> @@ -0,0 +1,14 @@
>> +ENTRY(foo);
>> +SECTIONS
>> +{
>> +       .text : ALIGN(4) {
>> +               *(.text*)
>> +       }
>> +
>> +       .data : ALIGN(4) {
>> +               __sec_start = .;
>> +               *(.gzdata)
>> +               __sec_end = .;
>> +       }
>> +}
>> +PROVIDE(__sec_size = __sec_end - 4);
> I do not know the legacy relocation scheme, but for tests I would try
> removing noise like ALIGN(4). .data output section containing .gzdata
> input sections looks strange too.
> Can .data input sections be used instead?

The __sec_end segment cannot be dumped using .data.

t:     file format elf64-loongarch


Disassembly of section .text:

0000000000000000 <foo>:
    0:    03400000     andi            $zero, $zero, 0x0
    4:    1c000004     pcaddu12i       $a0, 0
    8:    02c06084     addi.d          $a0, $a0, 24(0x18)
    c:    24000084     ldptr.w         $a0, $a0, 0
   10:    4c000020     jirl            $zero, $ra, 0

Disassembly of section .data:

0000000000000014 <__sec_start>:
   14:    00000001     0x00000001
>
> `__sec_size = __sec_end - 4` is unusual. Is `- 4` necessary to
> reproduce the bug? If necessary, add a comment.
Unnecessary, using "nop" before pcaddu12i instead.
>
>> diff --git a/ld/testsuite/ld-loongarch-elf/pcrel-const.s b/ld/testsuite/ld-loongarch-elf/pcrel-const.s
>> new file mode 100644
>> index 00000000000..bc4fb979a80
>> --- /dev/null
>> +++ b/ld/testsuite/ld-loongarch-elf/pcrel-const.s
>> @@ -0,0 +1,11 @@
>> +       .text
>> +       .align  2
>> +       .globl  foo
>> +       .type   foo, @function
>> +foo:
>> +       la.global       $r4,__sec_size
>> +       ldptr.w $r4,$r4,0
>> +       jr      $r1
>> +       .size   foo, .-foo
>> +       .data
>> +       .word 1
>> diff --git a/ld/testsuite/ld-loongarch-elf/pr.exp b/ld/testsuite/ld-loongarch-elf/pr.exp
>> new file mode 100644
>> index 00000000000..c0cc2fc30d2
>> --- /dev/null
>> +++ b/ld/testsuite/ld-loongarch-elf/pr.exp
>> @@ -0,0 +1,39 @@
>> +# Expect script for LoongArch ELF linker tests
>> +#   Copyright (C) 2022 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.
>> +#
>> +
>> +if ![istarget loongarch64-*-*] {
>> +  return
>> +}
>> +
>> +set link_tests [list \
>> +  [list \
>> +    "pcrel const" \
>> +    "-T pcrel-const.lds" "" \
>> +    "-mla-global-with-pcrel" \
>> +    { pcrel-const.s } \
>> +    [list \
>> +      [list objdump -D pcrel-const.d] \
>> +    ] \
>> +    "pcrel-const" \
>> +  ] \
>> +]
>> +
>> +run_ld_link_tests $link_tests
>> --
>> 2.31.1
>>