linux-kernel - Re: [RFC PATCH v2 00/17] objtool: Function validation tracing

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Message-ID: <jxvtccnmr35xtevd7kjd5tn4n4bpwvfo2baajidwv5yfsvqcvb@mj7t4zfpllm7>
Date: Tue, 23 Sep 2025 15:33:10 -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 PATCH v2 00/17] objtool: Function validation tracing

On Thu, Jun 19, 2025 at 04:56:42PM +0200, Alexandre Chartre wrote:
> Hi,
> 
> Version v2 of this RFC addresses all comments from Josh and Peter,
> in particular:
> 
> - add --disas option to disassemble functions
> - do not fail the build if libopcodes is not available. Instead objtool
>   is then built without disassembly support. In that case, objtool prints
>   a warning message if trying to use disassembly.
> 
>   Example:
>   $ ./tools/objtool/objtool --disas --link vmlinux.o
>   vmlinux.o: warning: objtool: Rebuild with libopcodes for disassembly support
>   
> - remove dbuffer
> - rename VTRACE* to TRACE*
> - add trace.[ch] for trace-related functions and macros

Sorry for the delay... this is looking really good.  A few nits I saw
when testing:

1) With "make -s" I see

  Auto-detecting system features:
  ...                                  libbfd: [ on  ]
  ...                disassembler-init-styled: [ on  ]

but I'm thinking that should be completely silent?

2) Also seeing an oddity with --trace:

  $ OBJTOOL_ARGS='--trace=shrink_node' make -s -j12 mm/vmscan.o
  shrink_node: validation begin
   12440:  shrink_node                                                 push   %rbp                                                -  - statecfa=rsp+16 rbp=(cfa-16) stack_size=16
   12440:  shrink_node                                                 push   %rbp
   12441:  shrink_node+0x1                                             mov    %rsp,%rbp                                           -  - statecfa=rbp+16
   12441:  shrink_node+0x1                                             mov    %rsp,%rbp

For the instructions which have unwinding state changes, it's printing
them twice.  Also the formatting looks a little off (two dashes;
"statecfa").

-- 
Josh