[PATCH] readelf: Add --plt-contents

[H.J. Lu]

On Tue, Sep 9, 2025 at 10:53 PM Jan Beulich <jbeulich@suse.com> wrote:
>
> 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?

objdump doesn't provide detailed ELF info like readelf does.

> >   The new code in readelf.c is around 900 lines.
>
> Which is a lot.
>
> Jan
>
> >  The rest are mostly tests.
> >
>


-- 
H.J.