linux-kernel - Re: [PATCH v6 03/30] objtool: Disassemble code with libopcodes instead of running objdump

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Message-ID: <3fa261fd-3b46-4cbe-b48d-7503aabc96cb@oracle.com>
Date: Wed, 26 Nov 2025 10:00:36 +0100
From: Alexandre Chartre <alexandre.chartre@...cle.com>
To: Nathan Chancellor <nathan@...nel.org>
Cc: alexandre.chartre@...cle.com, linux-kernel@...r.kernel.org,
        mingo@...nel.org, jpoimboe@...nel.org, peterz@...radead.org,
        david.laight.linux@...il.com
Subject: Re: [PATCH v6 03/30] objtool: Disassemble code with libopcodes
 instead of running objdump


On 11/25/25 19:16, Nathan Chancellor wrote:
> Hi Alexandre,
> 
> On Fri, Nov 21, 2025 at 10:53:13AM +0100, Alexandre Chartre wrote:
>> objtool executes the objdump command to disassemble code. Use libopcodes
>> instead to have more control about the disassembly scope and output.
>> If libopcodes is not present then objtool is built without disassembly
>> support.
>>
>> Signed-off-by: Alexandre Chartre <alexandre.chartre@...cle.com>
> ...
>> diff --git a/tools/objtool/include/objtool/arch.h b/tools/objtool/include/objtool/arch.h
>> index d89f8b5ec14e3..18c0e69ee6170 100644
>> --- a/tools/objtool/include/objtool/arch.h
>> +++ b/tools/objtool/include/objtool/arch.h
>> @@ -103,4 +103,13 @@ bool arch_absolute_reloc(struct elf *elf, struct reloc *reloc);
>>   unsigned int arch_reloc_size(struct reloc *reloc);
>>   unsigned long arch_jump_table_sym_offset(struct reloc *reloc, struct reloc *table);
>>   
>> +#ifdef DISAS
>> +
>> +#include <bfd.h>
> 
> This include of bfd.h breaks the build for me:
> 
>    $ make -skj"$(nproc)" ARCH=x86_64 CROSS_COMPILE=x86_64-linux- clean defconfig bzImage
>    In file included from tools/objtool/include/objtool/arch.h:108,
>                     from check.c:14:
>    /usr/include/bfd.h:35:2: error: #error config.h must be included before this header
>       35 | #error config.h must be included before this header
>          |  ^~~~~
>    ...
> 
> where my bfd.h has:
> 
>    #ifndef __BFD_H_SEEN__
>    #define __BFD_H_SEEN__
> 
>    /* PR 14072: Ensure that config.h is included first.  */
>    #if !defined PACKAGE && !defined PACKAGE_VERSION
>    #error config.h must be included before this header
>    #endif

This check is effectively present in the bfd.h file generated from the
binutils source code. However it is not present in the bfd.h file provided
by the binutils RPM. I think this explained why we haven't seen this issue
so far.

For history, this was introduced in 2012 for bug 14072. Then there was
complaints reported in bug 14243 and 15920. But it was decided not to
remove this change, and the suggested fix was to define PACKAGE when
including bfd.h.

https://sourceware.org/bugzilla/show_bug.cgi?id=14072
https://sourceware.org/bugzilla/show_bug.cgi?id=14243
https://sourceware.org/bugzilla/show_bug.cgi?id=15920

And Redhat has fixed the issue for the binutils RPM by removing this test:

https://sourceware.org/bugzilla/show_bug.cgi?id=14243


> Something like this cures it for me but I am not sure if that is a
> proper fix or not since I see config.h in my binutils build folder has
> many other defines.
> 
> Cheers,
> Nathan
> 
> diff --git a/tools/objtool/Makefile b/tools/objtool/Makefile
> index df793ca6fc1a..96df4a73da23 100644
> --- a/tools/objtool/Makefile
> +++ b/tools/objtool/Makefile
> @@ -87,7 +87,7 @@ BUILD_DISAS := n
>   
>   ifeq ($(feature-libbfd),1)
>   	BUILD_DISAS := y
> -	OBJTOOL_CFLAGS += -DDISAS
> +	OBJTOOL_CFLAGS += -DDISAS -DPACKAGE="objtool-disas"
>   	OBJTOOL_LDFLAGS += -lopcodes
>   endif
>   

This is the proper fix (as indicated in the binutils bugs), and this is
what the other kernel tools using bfd.h (bpf and perf) do. I will create
a patch with your suggestion.

Thanks,

alex.