linux-kernel - Re: [PATCH 02/18] objtool: Support data symbol printing

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Date:   Thu, 14 Apr 2022 18:36:51 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Miroslav Benes <mbenes@...e.cz>
Subject: Re: [PATCH 02/18] objtool: Support data symbol printing

On Thu, Apr 14, 2022 at 08:38:54AM -0700, Josh Poimboeuf wrote:

> > Yes, I'd not seen that yet, what's that for? The Changelog alludes to
> > something, but I don't think it actually does get used later.
> 
> Nick had asked for something like that, it's just a way to avoid doing
> math every time we look at a warning, i.e. to convert func+offset to
> sec+offset.
> 
> But it's kind of ugly and I'm not 100% happy with it.
> 
> Maybe it should be behind an option (--sec-offsets)?

Can do I suppose... Myself, I have this script:

$ cat objdump-func.sh
#!/bin/bash

OBJ=$1; shift
FUNC=$1; shift

objdump -wdr $@ $OBJ | awk "/^\$/ { P=0; } /$FUNC[^>]*>:\$/ { P=1; O=strtonum(\"0x\" \$1); } { if (P) { o=strtonum(\"0x\" \$1); printf(\"%04x \", o-O); print \$0; } }"

That prints a symbol relative offset next to the section, something
like:

$ ./objdump-func.sh defconfig-build/vmlinux.o pick_next_task_idle
0000 00000000000a9eb0 <pick_next_task_idle>:
0000    a9eb0:  41 54                   push   %r12
0002    a9eb2:  4c 8b a7 28 09 00 00    mov    0x928(%rdi),%r12
0009    a9eb9:  53                      push   %rbx
000a    a9eba:  48 89 fb                mov    %rdi,%rbx
000d    a9ebd:  66 90                   xchg   %ax,%ax
000f    a9ebf:  66 90                   xchg   %ax,%ax
0011    a9ec1:  4c 89 e0                mov    %r12,%rax
0014    a9ec4:  5b                      pop    %rbx
0015    a9ec5:  41 5c                   pop    %r12
0017    a9ec7:  c3                      ret    
0018    a9ec8:  e8 00 00 00 00          call   a9ecd <pick_next_task_idle+0x1d> a9ec9: R_X86_64_PLT32   __update_idle_core-0x4
001d    a9ecd:  eb f0                   jmp    a9ebf <pick_next_task_idle+0xf>
001f    a9ecf:  4c 89 e0                mov    %r12,%rax
0022    a9ed2:  83 83 b8 0b 00 00 01    addl   $0x1,0xbb8(%rbx)
0029    a9ed9:  5b                      pop    %rbx
002a    a9eda:  41 5c                   pop    %r12
002c    a9edc:  c3                      ret    
002d    a9edd:  0f 1f 00                nopl   (%rax)