[PATCH] readelf: Add --plt-contents

[Jan Beulich]

On 09.09.2025 20:49, H.J. Lu wrote:
> On Tue, Sep 9, 2025 at 3:24 AM Jan Beulich <jbeulich@suse.com> wrote:
>>
>> On 04.09.2025 15:41, H.J. Lu wrote:
>>> Add --plt-contents option to readelf to display contents of PLT sections.
>>> --plt-contents option requires:
>>>
>>> 1. The DT_JMPREL dynamic section for relocations associated with PLT
>>> entries.
>>> 2. Detailed PLT layout information to extract PLT relocation index and
>>> GOT index from PLT entries.
>>>
>>> When --plt-contents option is used:
>>>
>>> 1. Allocate an array, plt_relocations, to hold PLT relocations from the
>>> DT_JMPREL dynamic section.
>>> 2. Allocate an array, all_relocations, to hold all relocations to map
>>> GOT entries to corresponding symbols.
>>> 3. Process each PLT entry by extracting PLT relocation index and/or GOT
>>> index to display symbols or relocation associated with the PLT entry.
>>>
>>> Only i386 and x86-64 PLTs are supported.
>>
>> Which would need clarifying in doc, NEWS, and command line help.
> 
> Fixed in the v2 patch.
> 
>>> $ readelf --plt-contents libfoo.so
>>>
>>> Procedure Linkage Table '.plt' contains 3 entries:
>>>  Index:  Address GOT Idx GOT Addr Rel Idx Symbol/Reloc
>>>      0: 00000150
>>>      1: 00000160      3: 00200250      0: func
>>>      2: 00000170      4: 00200258      1: bar
>>>
>>> Procedure Linkage Table '.plt.got' contains 1 entry:
>>>  Index:  Address GOT Idx GOT Addr Symbol/Reloc
>>>      0: 00000180     -1: 00200230 foo
>>
>> That's omitting a lot of information. Isn't the disassembly of .plt quite
>> a bit more meaningful? I question whether the overall more than 3k lines
>> of new code (incl testcases) are really worth this new representation form.
>>
> 
> Adding disassembler to readelf is a separate issue.  In the meantime,
> objdump can be used.   --plt-contents provides a different set of
> information not available from objdump.

If objdump doesn't expose relevant information, maybe that's what wants
improving?

>   The new code in readelf.c is around 900 lines.

Which is a lot.

Jan

>  The rest are mostly tests.
>