[PATCH,V3 9/9] ld: bfd: sframe: Update section size also for relocatable links

[Indu Bhagat]

On 6/16/25 12:26 AM, Jan Beulich wrote:
> On 16.06.2025 08:47, Indu Bhagat wrote:
>> On 6/13/25 5:53 AM, Jan Beulich wrote:
>>> On 13.06.2025 09:32, Indu Bhagat wrote:
>>>> From: Jens Remus <jremus@linux.ibm.com>
>>>>
>>>> For relocatable links the output .sframe section size may be wrong.
>>>> This can be observed when dumping the SFrame information from the x86-64
>>>> sframe-reloc-1 test:
>>>>
>>>> Name              Address          Off    Size
>>>> .sframe           0000000000000000 000110 00007f
>>>>
>>>> Offset            Type               Symbol's Value  Symbol's Name + Addend
>>>> 000000000000001c  R_X86_64_PC32      0000000000000000 .text + 1c
>>>> 0000000000000030  R_X86_64_PC32      0000000000000000 .text + 65
>>>>
>>>> 0x00000000 e2de0201 0300f800 02000000 08000000 ................
>>>> 0x00000010 1e000000 00000000 28000000 00000000 ........(.......
>>>> 0x00000020 35000000 00000000 04000000 00000000 5...............
>>>> 0x00000030 00000000 25000000 0f000000 04000000 ....%...........
>>>>               offset 1st FRE---^^^^^^^^ ^^^^^^^^---number of FREs
>>>> 0x00000040 00000000 00030801 0510f004 0410f034 ...............4
>>>> FDE info---^^      | begin of FDEs
>>>> 0x00000050 0508f000 03080105 10f00404 10f02405 ..............$.
>>>>                    11111112222222223333333334444---FRE 1, 2, 3, 4
>>>> 0x00000060 08f00000 00000000 00000000 00000000 ................
>>>>              4444^^^^...
>>>> 0x00000070 00000000 00000000 00000000 000000   ...............
>>>>                                      ...^^^^^^---excessive section
>>>>
>>>> When running the x86-64 test cross build on a big-endian system, such
>>>> as s390x, objdump and readelf fail to dump the SFrame information with
>>>> the following error message:
>>>>
>>>> Error: SFrame decode failure: Buffer does not contain SFrame data.
>>>>
>>>> This is because the following check in flip_sframe() fails, which gets
>>>> only invoked if the endianness of the SFrame data is different from the
>>>> host system one:
>>>>
>>>> /* All FDEs and FREs must have been endian flipped by now.  */
>>>> if ((j != ihp->sfh_num_fres) || (bytes_flipped != (buf_size - hdrsz)))
>>>>                                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>>
>>>> With:
>>>> j=8, ihp->sfh_num_fres=8, bytes_flipped=70, buf_size=127, hdrsz=28
>>>
>>> All of this describes the symptom pretty extensively. However, ...
>>>
>>>> --- a/bfd/elf-sframe.c
>>>> +++ b/bfd/elf-sframe.c
>>>> @@ -660,13 +660,11 @@ _bfd_elf_write_section_sframe (bfd *abfd, struct bfd_link_info *info)
>>>>    				 (file_ptr) sec->output_offset,
>>>>    				 sec->size))
>>>>        retval = false;
>>>> -  else if (!bfd_link_relocatable (info))
>>>> +  else
>>>>        {
>>>>          Elf_Internal_Shdr *hdr = &elf_section_data (sec)->this_hdr;
>>>>          hdr->sh_size = sec->size;
>>>>        }
>>>> -  /* For relocatable links, do not update the section size as the section
>>>> -     contents have not been relocated.  */
>>>
>>> ... it doesn't become clear in how far this comment was wrong, and hence
>>> why for relocatable links the size also needs updating. (And yes, the
>>> connection between "has been relocated" and "size needs updating" looks
>>> suspect to me, but what's wrong with that wants calling out imo.)
>>>
>>
>> I do not recall why this comment was added originally, and I cannot make
>> sense of this one now either.  I dont see the connection between "do not
>> update size" because the "contents have not been relocated" ATM...
> 
> This (and hence things simply having been bogus) may then want adding to the
> description.
> 

OK. I have added a one liner:

While at it, remove the incorrect code comment.  There is no
relationship between "do not update size" and the fact that the
"contents have not been relocated".

Thanks for reviewing