linux-kernel - Re: [RFC 00/13] objtool: Function validation tracing

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Message-ID: <vx6cxar2ium7zsqqzf57lmn2nhwemi2kmeu2kal6s4mazj3tp3@zdymccnsispv>
Date: Mon, 9 Jun 2025 11:31:30 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Alexandre Chartre <alexandre.chartre@...cle.com>
Cc: linux-kernel@...r.kernel.org, mingo@...nel.org, peterz@...radead.org
Subject: Re: [RFC 00/13] objtool: Function validation tracing

On Fri, Jun 06, 2025 at 05:34:27PM +0200, Alexandre Chartre wrote:
> Hi,
> 
> This RFC provides two changes to objtool.
> 
> - Disassemble code with libopcodes instead of running objdump
> 
>   objtool executes the objdump command to disassemble code. In particular,
>   if objtool fails to validate a function then it will use objdump to
>   disassemble the entire file which is not very helpful when processing
>   a large file (like vmlinux.o).
> 
>   Using libopcodes provides more control about the disassembly scope and
>   output, and it is possible to disassemble a single instruction or
>   a single function. Now when objtool fails to validate a function it
>   will disassemble that single function instead of disassembling the
>   entire file.
> 
> - Add the --trace <function> option to trace function validation
> 
>   Figuring out why a function validation has failed can be difficult because
>   objtool checks all code flows (including alternatives) and maintains
>   instructions states (in particular call frame information).
> 
>   The trace option allows to follow the function validation done by objtool
>   instruction per instruction, see what objtool is doing and get function
>   validation information. An output example is shown below.

What do I need for this to build?  It wasn't compiling due to missing
bfd.h, so I installed binutils-devel (Fedora) and now I get:

In file included from disas.c:12:
/home/jpoimboe/git/linux/tools/include/tools/dis-asm-compat.h:10:6: error: redeclaration of ‘enum disassembler_style’
   10 | enum disassembler_style {DISASSEMBLER_STYLE_NOT_EMPTY};
      |      ^~~~~~~~~~~~~~~~~~
In file included from /home/jpoimboe/git/linux/tools/objtool/include/objtool/arch.h:10,
                 from disas.c:6:
/usr/include/dis-asm.h:53:6: note: originally defined here
   53 | enum disassembler_style
      |      ^~~~~~~~~~~~~~~~~~
/home/jpoimboe/git/linux/tools/include/tools/dis-asm-compat.h: In function ‘init_disassemble_info_compat’:
/home/jpoimboe/git/linux/tools/include/tools/dis-asm-compat.h:50:9: error: too few arguments to function ‘init_disassemble_info’
   50 |         init_disassemble_info(info, stream,
      |         ^~~~~~~~~~~~~~~~~~~~~
/usr/include/dis-asm.h:480:13: note: declared here
  480 | extern void init_disassemble_info (struct disassemble_info *dinfo, void *stream,
      |             ^~~~~~~~~~~~~~~~~~~~~
make[4]: *** [/home/jpoimboe/git/linux/tools/build/Makefile.build:86: /home/jpoimboe/git/linux/tools/objtool/disas.o] Error 1
make[4]: *** Waiting for unfinished jobs....
make[3]: *** [Makefile:65: /home/jpoimboe/git/linux/tools/objtool/objtool-in.o] Error 2
make[2]: *** [Makefile:73: objtool] Error 2
make[1]: *** [/home/jpoimboe/git/linux/Makefile:1448: tools/objtool] Error 2
make: *** [Makefile:248: __sub-make] Error 2

-- 
Josh