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SubjectRe: [PATCH v2] scripts: Create objdump-func helper script
On Tue, Apr 19, 2022 at 09:50:01PM +0200, Borislav Petkov wrote:
> On Tue, Apr 19, 2022 at 09:12:23AM -0700, Josh Poimboeuf wrote:
> > Add a simple script which disassembles a single function from an object
> > file. Comes in handy for objtool warnings and kernel stack traces.
> >
> > Originally-by: Peter Zijlstra <peterz@infradead.org>
> > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> > ---
> > v2:
> > - require gawk
> >
> > scripts/objdump-func | 18 ++++++++++++++++++
> > 1 file changed, 18 insertions(+)
> > create mode 100755 scripts/objdump-func
>
> Was that supposed to be user-friendly too?
>
> $ ./scripts/objdump-func -h
> ./scripts/objdump-func: line 16: $1: unbound variable
>
> :-)
>
>
> It works tho:
>
> $ ./scripts/objdump-func vmlinux rewind_stack_and_make_dead
> 0000 ffffffff81001c00 <rewind_stack_and_make_dead>:
> 0000 ffffffff81001c00: 31 ed xor %ebp,%ebp
> 0000 ffffffff81001c02: 65 48 8b 04 25 d0 ec 01 00 mov %gs:0x1ecd0,%rax
> 0000 ffffffff81001c0b: 48 8d a0 58 ff ff ff lea -0xa8(%rax),%rsp
> 0000 ffffffff81001c12: e8 39 24 07 00 call ffffffff81074050 <make_task_dead>
> ^^^^
>
> I guess those zeros at the beginning are supposed to mean something...

Use the .o file and it'll work:

$ ./objdump-func.sh defconfig-build/vmlinux.o rewind_stack_and_make_dead
0000 0000000000001380 <rewind_stack_and_make_dead>:
0000 1380: 31 ed xor %ebp,%ebp
0002 1382: 65 48 8b 04 25 00 00 00 00 mov %gs:0x0,%rax 1387: R_X86_64_32S cpu_current_top_of_stack
000b 138b: 48 8d a0 58 ff ff ff lea -0xa8(%rax),%rsp
0012 1392: e8 00 00 00 00 call 1397 <preempt_schedule_thunk> 1393: R_X86_64_PLT32 make_task_dead-0x4


Now the first coloumn is the symbol relative offset, while the second
column is the section relative offset objdump normally gives you.

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