[PATCH 1/2] libsframe: add new dump_sframe_reloc

[Indu Bhagat]

On 2/19/25 1:38 AM, Jan Beulich wrote:
> On 17.02.2025 17:58, Indu Bhagat wrote:
>> --- a/libsframe/sframe.c
>> +++ b/libsframe/sframe.c
>> @@ -102,6 +102,37 @@ sframe_ret_set_errno (int *errp, int error)
>>     return NULL;
>>   }
>>   
>> +/* If the input buffer containing the SFrame section has been relocated, there
>> +   will be a need to do fixups too.  The fixup merely accounts for the offset
>> +   of the byte from the start of the section.
>> +
>> +   Currently used by dump_sframe_reloc.  The caller must have decoded (and
>> +   hence, endian flipped) the input buffer before calling this function.  */
>> +
>> +int
>> +sframe_fde_tbl_reloc_fixup (sframe_decoder_ctx *dctx)
>> +{
>> +  uint8_t sframe_ver = sframe_decoder_get_version (dctx);
>> +  uint32_t num_fdes = sframe_decoder_get_num_fidx (dctx);
>> +  unsigned int buf_offset = 0;
>> +  sframe_func_desc_entry *fde;
>> +  uint32_t i = 0;
>> +
>> +  if (sframe_ver != SFRAME_VERSION_2 || !dctx->sfd_funcdesc)
>> +    return SFRAME_ERR;
>> +
>> +  buf_offset += sframe_decoder_get_hdr_size (dctx);
>> +  while (i < num_fdes)
>> +    {
>> +      fde = &dctx->sfd_funcdesc[i];
>> +      fde->sfde_func_start_address += buf_offset;
>> +      buf_offset += sizeof (sframe_func_desc_entry);
>> +      i++;
>> +    }
>> +
>> +  return 0;
>> +}
> 
> In the bug report, comment 1, you specifically provided
> 
> $ readelf -r file.o
> Relocation section '.rela.sframe' at offset 0x8728 contains 3 entries:
>    Offset          Info           Type           Sym. Value    Sym. Name + Addend
> 00000000001c  000200000002 R_X86_64_PC32     0000000000000000 .text + 0
> 000000000030  000200000002 R_X86_64_PC32     0000000000000000 .text + 30
> 000000000044  000200000002 R_X86_64_PC32     0000000000000000 .text + 40
> 
> Having peeked also at patch 2, I fail to see where these relocations
> are actually applied. The function above appears to be making assumptions
> about where relocations need applying, and why type they are. Am I
> overlooking anything?
> 

The reloc machinery is invoked in the load_specific_debug_section () 
functions.

Not sure if it is not clear from code comments: Such reloc fixup for 
pc-relative relocations is necessary only for the usecase of textual 
dump of the debug sections containing relocations.