Re: [PATCH] backends: add checks for _GLOBAL_OFFSET_TABLE_ on loongarch

[Youling Tang <tangyouling@loongson.cn>]

Hi, Hengqi

On 04/04/2023 11:45 PM, Hengqi Chen wrote:
> Hi, Youling
>
> On Sat, Apr 1, 2023 at 11:19 AM Youling Tang <tangyouling@loongson.cn> wrote:
>>
>> Add handling of _GLOBAL_OFFSET_TABLE_.
>>
>> Before applying the patch:
>> $ ./src/elflint --gnu-ld ./src/elflint
>> section [35] '.symtab': _GLOBAL_OFFSET_TABLE_ symbol value 0x68548
>> does not match .got.plt section address 0x68238
>>
>> After applying the patch:
>> $ ./src/elflint --gnu-ld ./src/elflint
>> No errors
>>
>> Signed-off-by: Liwei Ge <geliwei@openanolis.org>
>> Signed-off-by: Youling Tang <tangyouling@loongson.cn>
>> ---
>>  backends/ChangeLog          |  4 ++++
>>  backends/loongarch_init.c   |  1 +
>>  backends/loongarch_symbol.c | 35 +++++++++++++++++++++++++++++++++++
>>  3 files changed, 40 insertions(+)
>>
>> diff --git a/backends/ChangeLog b/backends/ChangeLog
>> index 81f08314..41071953 100644
>> --- a/backends/ChangeLog
>> +++ b/backends/ChangeLog
>> @@ -1,3 +1,7 @@
>> +2023-04-01  Youling Tang <tangyouling@loongson.cn>
>> +       * loongarch_init.c (loongarch_init): Hook check_special_symbol.
>> +       * loongarch_symbol.c (loongarch_check_special_symbol): New function.
>> +
>>  2023-02-07  Mark Wielaard  <mark@klomp.org>
>>
>>         * libebl_CPU.h (dwarf_peeled_die_type): Explicitly handle
>> diff --git a/backends/loongarch_init.c b/backends/loongarch_init.c
>> index 59d8cc3d..b641b07f 100644
>> --- a/backends/loongarch_init.c
>> +++ b/backends/loongarch_init.c
>> @@ -46,6 +46,7 @@ loongarch_init (Elf *elf __attribute__ ((unused)),
>>    loongarch_init_reloc (eh);
>>    HOOK (eh, reloc_simple_type);
>>    HOOK (eh, machine_flag_check);
>> +  HOOK (eh, check_special_symbol);
>>
>>    return eh;
>>  }
>> diff --git a/backends/loongarch_symbol.c b/backends/loongarch_symbol.c
>> index 43306ab8..5ce55bad 100644
>> --- a/backends/loongarch_symbol.c
>> +++ b/backends/loongarch_symbol.c
>> @@ -79,3 +79,38 @@ loongarch_machine_flag_check (GElf_Word flags)
>>    return ((flags &~ (EF_LARCH_ABI_MODIFIER_MASK
>>                      | EF_LARCH_OBJABI_V1)) == 0);
>>  }
>> +
>> +/* Check whether given symbol's st_value and st_size are OK despite failing
>> +   normal checks.  */
>> +bool
>> +loongarch_check_special_symbol (Elf *elf, const GElf_Sym *sym,
>> +                           const char *name, const GElf_Shdr *destshdr)
>> +{
>> +  if (name != NULL
>> +      && strcmp (name, "_GLOBAL_OFFSET_TABLE_") == 0)
>> +    {
>> +      size_t shstrndx;
>> +      if (elf_getshdrstrndx (elf, &shstrndx) != 0)
>> +       return false;
>> +      const char *sname = elf_strptr (elf, shstrndx, destshdr->sh_name);
>> +      if (sname != NULL
>> +         && (strcmp (sname, ".got") == 0 || strcmp (sname, ".got.plt") == 0))
>> +       {
>> +         Elf_Scn *scn = NULL;
>> +         while ((scn = elf_nextscn (elf, scn)) != NULL)
>> +           {
>> +             GElf_Shdr shdr_mem;
>> +             GElf_Shdr *shdr = gelf_getshdr (scn, &shdr_mem);
>> +             if (shdr != NULL)
>> +               {
>> +                 sname = elf_strptr (elf, shstrndx, shdr->sh_name);
>> +                 if (sname != NULL && strcmp (sname, ".got") == 0)
>> +                   return (sym->st_value >= shdr->sh_addr
>> +                           && sym->st_value < shdr->sh_addr + shdr->sh_size);
>> +               }
>> +           }
>> +       }
>> +    }
>> +
>> +  return false;
>> +}
>> --
>> 2.37.1
>>
>
> I've tested this locally, but still remains one error:
> section [34] '.symtab': _DYNAMIC symbol size 0 does not match dynamic
> segment size 480

The problem should be independent of this patch, but I can't reproduce
it.

- Test Environment 1: Old Toolchain:
$ cat /etc/os-release
NAME="My GNU/Linux System for LoongArch64"
VERSION="5.0"
ID=CLFS4LA64
PRETTY_NAME="My GNU/Linux System for LoongArch64 5.0"

$ gcc -v
gcc version 12.1.0 (GCC)

$ ./src/elflint --gnu-ld ./src/elflint
No errors


- Test Environment 2: New Toolchain:
$ cat /etc/os-release
NAME="My GNU/Linux System for LoongArch64"
VERSION="6.0"
ID=CLFS4LA64
PRETTY_NAME="My GNU/Linux System for LoongArch64 6.0"

$ gcc -v
gcc version 13.0.0 20220919 (experimental) (GCC)

$ ./src/elflint --gnu-ld ./src/elflint
No errors

Can you provide your test environment, or help debug the possible
causes of the problem?

Thanks,
Youling.