[Bug binutils/30979] New: objdump --disassemble of a .o file ignores the relocations

[bruno at clisp dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30979

            Bug ID: 30979
           Summary: objdump --disassemble of a .o file ignores the
                    relocations
           Product: binutils
           Version: 2.38
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: binutils
          Assignee: unassigned at sourceware dot org
          Reporter: bruno at clisp dot org
  Target Milestone: ---

Created attachment 15178
  --> https://sourceware.org/bugzilla/attachment.cgi?id=15178&action=edit
sample object file

When 'objdump' is invoked to disassemble a .o file, it ignores
the relocations and thus prints nonsense for the targets of
calls to functions outside this .o file.

Example: On x64_64:
========================================================================
$ objdump --disassemble fenv-round.o
fenv-round.o:     file format elf64-x86-64


Disassembly of section .text:

0000000000000000 <fegetround>:
   0:   f3 0f 1e fa             endbr64 
   4:   48 83 ec 18             sub    $0x18,%rsp
   8:   64 48 8b 04 25 28 00    mov    %fs:0x28,%rax
   f:   00 00 
  11:   48 89 44 24 08          mov    %rax,0x8(%rsp)
  16:   31 c0                   xor    %eax,%eax
  18:   d9 7c 24 06             fnstcw 0x6(%rsp)
  1c:   0f b7 44 24 06          movzwl 0x6(%rsp),%eax
  21:   25 00 0c 00 00          and    $0xc00,%eax
  26:   48 8b 54 24 08          mov    0x8(%rsp),%rdx
  2b:   64 48 2b 14 25 28 00    sub    %fs:0x28,%rdx
  32:   00 00 
  34:   75 05                   jne    3b <fegetround+0x3b>
  36:   48 83 c4 18             add    $0x18,%rsp
  3a:   c3                      ret    
  3b:   e8 00 00 00 00          call   40 <fesetround>

0000000000000040 <fesetround>:
  40:   f3 0f 1e fa             endbr64 
  44:   48 83 ec 28             sub    $0x28,%rsp
  48:   41 89 f8                mov    %edi,%r8d
  4b:   64 48 8b 04 25 28 00    mov    %fs:0x28,%rax
  52:   00 00 
  54:   48 89 44 24 18          mov    %rax,0x18(%rsp)
  59:   31 c0                   xor    %eax,%eax
  5b:   41 81 e0 ff f3 ff ff    and    $0xfffff3ff,%r8d
  62:   75 5c                   jne    c0 <fesetround+0x80>
  64:   d9 7c 24 0e             fnstcw 0xe(%rsp)
  68:   0f b7 54 24 0e          movzwl 0xe(%rsp),%edx
  6d:   89 d0                   mov    %edx,%eax
  6f:   80 e4 f3                and    $0xf3,%ah
  72:   09 f8                   or     %edi,%eax
  74:   66 89 44 24 0c          mov    %ax,0xc(%rsp)
  79:   66 39 c2                cmp    %ax,%dx
  7c:   74 04                   je     82 <fesetround+0x42>
  7e:   d9 6c 24 0c             fldcw  0xc(%rsp)
  82:   0f ae 5c 24 14          stmxcsr 0x14(%rsp)
  87:   8b 54 24 14             mov    0x14(%rsp),%edx
  8b:   c1 e7 03                shl    $0x3,%edi
  8e:   89 d0                   mov    %edx,%eax
  90:   80 e4 9f                and    $0x9f,%ah
  93:   09 f8                   or     %edi,%eax
  95:   89 44 24 10             mov    %eax,0x10(%rsp)
  99:   39 c2                   cmp    %eax,%edx
  9b:   74 05                   je     a2 <fesetround+0x62>
  9d:   0f ae 54 24 10          ldmxcsr 0x10(%rsp)
  a2:   48 8b 44 24 18          mov    0x18(%rsp),%rax
  a7:   64 48 2b 04 25 28 00    sub    %fs:0x28,%rax
  ae:   00 00 
  b0:   75 16                   jne    c8 <fesetround+0x88>
  b2:   44 89 c0                mov    %r8d,%eax
  b5:   48 83 c4 28             add    $0x28,%rsp
  b9:   c3                      ret    
  ba:   66 0f 1f 44 00 00       nopw   0x0(%rax,%rax,1)
  c0:   41 b8 ff ff ff ff       mov    $0xffffffff,%r8d
  c6:   eb da                   jmp    a2 <fesetround+0x62>
  c8:   e8 00 00 00 00          call   cd <fesetround+0x8d>
========================================================================

The last instruction of the first function is particularly misleading:
It looks like a call function <fesetround>. Which it isn't, as can be
seen from
========================================================================
$ objdump --reloc fenv-round.o

fenv-round.o:     file format elf64-x86-64

RELOCATION RECORDS FOR [.text]:
OFFSET           TYPE              VALUE 
000000000000003c R_X86_64_PLT32    __stack_chk_fail-0x0000000000000004
...
========================================================================

or from disassembling an executable that was linked with this object file:

========================================================================
$ objdump --disassemble test-fenv-round
...
0000000000001cb0 <fegetround>:
    1cb0:       f3 0f 1e fa             endbr64 
    1cb4:       48 83 ec 18             sub    $0x18,%rsp
    1cb8:       64 48 8b 04 25 28 00    mov    %fs:0x28,%rax
    1cbf:       00 00 
    1cc1:       48 89 44 24 08          mov    %rax,0x8(%rsp)
    1cc6:       31 c0                   xor    %eax,%eax
    1cc8:       d9 7c 24 06             fnstcw 0x6(%rsp)
    1ccc:       0f b7 44 24 06          movzwl 0x6(%rsp),%eax
    1cd1:       25 00 0c 00 00          and    $0xc00,%eax
    1cd6:       48 8b 54 24 08          mov    0x8(%rsp),%rdx
    1cdb:       64 48 2b 14 25 28 00    sub    %fs:0x28,%rdx
    1ce2:       00 00 
    1ce4:       75 05                   jne    1ceb <fegetround+0x3b>
    1ce6:       48 83 c4 18             add    $0x18,%rsp
    1cea:       c3                      ret    
    1ceb:       e8 a0 f3 ff ff          call   1090 <__stack_chk_fail@plt>

...
========================================================================

Even the combined options --disassemble and --reloc don't produce a
human-readable result:
========================================================================
$ objdump --disassemble --reloc test-fenv-round
...
  3b:   e8 00 00 00 00          call   40 <fesetround>
                        3c: R_X86_64_PLT32      __stack_chk_fail-0x4
...
========================================================================
(The "40 <fesetround>" part is still nonsense. And what is the -0x4 here??)

What I would want to see, is:
========================================================================
$ objdump --disassemble test-fenv-round
...
  3b:   e8 00 00 00 00          call   <__stack_chk_fail@plt>
...
========================================================================

Because of this problem, "objdump --disassemble" on .o files is
effectively useless to me in most situations.

$ objdump --version
GNU objdump (GNU Binutils for Ubuntu) 2.38

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