<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/62537>62537</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            llvm-objdump does not disassembly PLT subs of some DSOs produced by GNU toolchain.
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          dougkwan
      </td>
    </tr>
</table>

<pre>
    Some toolchains (e.g. gcc 12) may create shared objects  without .got.plt sections and use .got for PLT entires. llvm-objdump fails to disassemble PLT stub entries of such objects. The followings show outputs from llvm-objdump and objdump in GNU binutils.

The problem with the current llvm-objdump is that it just looks for the .got.plt section. If it is absent, it does not add any PLT symbols. Some toolchains may not use a separate .got.plt section and just use a single .got section bot both PLT and non-PLT dynamic relocations.

1. Disassembly produced by a recent version of llvm-objdump. Note the PLT stub at 0x2040 without a label.

Disassembly of section .plt:

0000000000002020 <.plt>:

    ...

    2036: 68 00 00 00 00                pushq $0x0
    203b: e9 e0 ff ff ff                jmp     0x2020 <.plt>
 2040: ff 25 72 ce 00 00             jmpq    *0xce72(%rip)           # 0xeeb8 <_GLOBAL_OFFSET_TABLE_+0x20>
    2046: 68 01 00 00 00                pushq $0x1
    204b: e9 d0 ff ff ff                jmp     0x2020 <.plt>
 2050: ff 25 6a ce 00 00             jmpq    *0xce6a(%rip)           # 0xeec0 <_GLOBAL_OFFSET_TABLE_+0x28>
    2056: 68 02 00 00 00                pushq $0x2
    205b: e9 c0 ff ff ff                jmp     0x2020 <.plt>
 2060: ff 25 62 ce 00 00             jmpq    *0xce62(%rip)           # 0xeec8 <_GLOBAL_OFFSET_TABLE_+0x30>
    2066: 68 03 00 00 00                pushq $0x3

2. Disassembly by gnu objdump:

Disassembly of section .plt:

   ...

    2036:       68 00 00 00 00          push $0x0
    203b:       e9 e0 ff ff ff          jmp    2020 <_init+0x20>

0000000000002040 <sb_newf@plt>:
    2040:       ff 25 72 ce 00 00       jmp    *0xce72(%rip)        # eeb8 <sb_newf@Base>
 2046:       68 01 00 00 00          push   $0x1
    204b:       e9 d0 ff ff ff          jmp    2020 <_init+0x20>

I believe the problem is at least in llvm-project/llvm/lib/Object/ELFObjectFile.cpp.  The following patch fixes this particular instance of the problem but I was told that it is incomplete as the "-z lazy" case is not handled.

==== a/llvm/lib/Object/ELFObjectFile.cpp#46 - b/llvm/llvm-project/llvm/lib/Object/ELFObjectFile.cpp ====
627c627
< std::optional<SectionRef> Plt, RelaPlt, GotPlt;
---
> std::optional<SectionRef> Plt, RelaPlt, GotPlt, Got;
641a642,643
> else if (Name == ".got")
>       Got = Section;
643c645,650
<   if (!Plt || !RelaPlt || !GotPlt)
---
> 
>   // Some toolchains do not use a seperate .got.plt section. Fall back
>   // to .got if .got.plt is absent.
>   std::optional<SectionRef> GotToSearch = GotPlt ? GotPlt : Got;
> 
>   if (!Plt || !RelaPlt || !GotToSearch)
652c659
< GotPlt->getAddress(), Triple);
---
> GotToSearch->getAddress(), Triple);


</pre>
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