Re: [PATCH v4] PR30592 objcopy: allow --set-section-flags to add or remove SHF_X86_64_LARGE

[Fangrui Song <maskray@google.com>]

On 2023-07-10, Jan Beulich wrote:
>On 08.07.2023 07:30, Fangrui Song via Binutils wrote:
>> --- a/bfd/section.c
>> +++ b/bfd/section.c
>> @@ -359,6 +359,9 @@ CODE_FRAGMENT
>>  .     TMS320C54X only.  *}
>>  .#define SEC_TIC54X_BLOCK           0x10000000
>>  .
>> +.  {* This section has the SHF_X86_64_LARGE flag.  This is ELF x86-64 only.  *}
>> +.#define SEC_ELF_LARGE              0x10000000
>> +.
>>  .  {* Conditionally link this section; do not link if there are no
>>  .     references found to any symbol in the section.  This is for TI
>>  .     TMS320C54X only.  *}
>> @@ -2618,7 +2621,7 @@ merge_gnu_build_notes (bfd *          abfd,
>>  }
>>
>>  static flagword
>> -check_new_section_flags (flagword flags, bfd * abfd, const char * secname)
>> +check_new_section_flags (flagword flags, bfd *abfd, const char * secname)
>
>Nit: Stray (and inconsistent) change?

Sorry, this was an unneeded change.

I guess I formatted this line either in editor or via .clang-format but
I reverted `const char *secname` but not `bfd *abfd`...

>> @@ -2631,6 +2634,19 @@ check_new_section_flags (flagword flags, bfd * abfd, const char * secname)
>>  		 bfd_get_filename (abfd), secname);
>>        flags &= ~ SEC_COFF_SHARED;
>>      }
>> +
>> +  /* Report a fatal error if 'large' is used with a non-x86-64 ELF target.
>> +     Suppress the error for non-ELF targets to allow -O binary and formats that
>> +     use the bit value SEC_ELF_LARGE for other purposes.  */
>> +  if ((flags & SEC_ELF_LARGE) != 0
>> +      && bfd_get_flavour (abfd) == bfd_target_elf_flavour
>> +      && get_elf_backend_data (abfd)->elf_machine_code != EM_X86_64)
>
>DYM
>
>  if ((flags & SEC_ELF_LARGE) != 0
>      && (bfd_get_flavour (abfd) != bfd_target_elf_flavour
>	  || get_elf_backend_data (abfd)->elf_machine_code != EM_X86_64))
>
>?
>
>Jan

I do mean that this check is fired only when the output bfd (abfd) is
ELF and the architecture is different from x86-64.

The bit value SEC_ELF_LARGE is shared with other object file formats
(COFF SEC_TIC54X_BLOCK; I don't know what this target is).
If TMS320C54X has a section with the SEC_TIC54X_BLOCK flag, we
don't want to report a fatal error.

In addition, abfd may specify a non-ELF bfd, e.g.,

     objcopy --set-section-flags .data=alloc,large -I elf64-x86-64 -O binary a.o a.bin

I assume that this case should receive no warning/error, just like how
many other flags like 'load', 'noload' behave today.

>> +    {
>> +      fatal (_ ("%s[%s]: 'large' flag is ELF x86-64 specific"),
>> +	     bfd_get_filename (abfd), secname);
>> +      flags &= ~SEC_ELF_LARGE;
>> +    }
>> +
>>    return flags;
>>  }
>>
>
>