linux-kernel - Re: [RFC 03/13] objtool: Disassemble code with libopcodes instead of running objdump

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Message-ID: <25ae649b-8f0b-447e-8e50-87444c0ea9da@oracle.com>
Date: Wed, 11 Jun 2025 15:35:38 +0200
From: Alexandre Chartre <alexandre.chartre@...cle.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: alexandre.chartre@...cle.com, linux-kernel@...r.kernel.org,
        mingo@...nel.org, jpoimboe@...nel.org
Subject: Re: [RFC 03/13] objtool: Disassemble code with libopcodes instead of
 running objdump


On 6/11/25 14:23, Peter Zijlstra wrote:
> On Fri, Jun 06, 2025 at 05:34:30PM +0200, Alexandre Chartre wrote:
>> objtool executes the objdump command to disassemble code. Use libopcodes
>> instead to have more control about the disassembly scope and output.
>>
>> Signed-off-by: Alexandre Chartre <alexandre.chartre@...cle.com>
>> ---
>>   tools/objtool/Makefile                  |   2 +-
>>   tools/objtool/arch/loongarch/decode.c   |   6 +
>>   tools/objtool/arch/powerpc/decode.c     |   6 +
>>   tools/objtool/arch/x86/decode.c         |   7 +
>>   tools/objtool/check.c                   |   4 +-
>>   tools/objtool/disas.c                   | 186 +++++++++++++++---------
>>   tools/objtool/include/objtool/arch.h    |   5 +
>>   tools/objtool/include/objtool/check.h   |   5 +
>>   tools/objtool/include/objtool/objtool.h |   4 +
>>   9 files changed, 154 insertions(+), 71 deletions(-)
>>
>> diff --git a/tools/objtool/Makefile b/tools/objtool/Makefile
>> index 8c20361dd100..00350fc7c662 100644
>> --- a/tools/objtool/Makefile
>> +++ b/tools/objtool/Makefile
>> @@ -34,7 +34,7 @@ INCLUDES := -I$(srctree)/tools/include \
>>   # is passed here to match a legacy behavior.
>>   WARNINGS := $(EXTRA_WARNINGS) -Wno-switch-default -Wno-switch-enum -Wno-packed -Wno-nested-externs
>>   OBJTOOL_CFLAGS := -Werror $(WARNINGS) $(KBUILD_HOSTCFLAGS) -g $(INCLUDES) $(LIBELF_FLAGS)
>> -OBJTOOL_LDFLAGS := $(LIBELF_LIBS) $(LIBSUBCMD) $(KBUILD_HOSTLDFLAGS)
>> +OBJTOOL_LDFLAGS := $(LIBELF_LIBS) $(LIBSUBCMD) $(KBUILD_HOSTLDFLAGS) -lopcodes
> 
> Would it be possible to make this optional? Such that when people do not
> have libopcodes installed they can still build the kernel.
> 
> Or is libopcodes a mandatory part of any binutils installation?

I guess that libopcodes is mandatory because it is used by as (and also objdump).
But I can check if it is effectively present anyway.

alex.