[PATCH] backends: add checks for _GLOBAL_OFFSET_TABLE_ on loongarch

[Hengqi Chen]

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

Cheers,
---
Hengqi