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

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Message-ID: <89da2d1e-698c-488a-b634-eafcb4dcb31a@oracle.com>
Date: Wed, 10 Dec 2025 17:36:07 +0100
From: Alexandre Chartre <alexandre.chartre@...cle.com>
To: Guenter Roeck <linux@...ck-us.net>,
        "Maciej W. Rozycki"
 <macro@...am.me.uk>
Cc: alexandre.chartre@...cle.com, linux-kernel@...r.kernel.org,
        Ingo Molnar <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 12/10/25 16:26, Guenter Roeck wrote:
> On 12/9/25 23:53, Alexandre Chartre wrote:
>>
>>
>> On 12/10/25 06:08, Guenter Roeck wrote:
>>> On 12/9/25 14:25, Maciej W. Rozycki wrote:
>>>> On Tue, 9 Dec 2025, Alexandre Chartre wrote:
>>>>
>>>>>> Bisect log is attached. I see the problem with gcc 11.4.0, 13.3.0, and
>>>>>> 14.3.0. I tried with both Ubuntu 22.04 and 24.04.
>>>>>
>>>>> This sounds like a configuration issue depending on the binutils version; in
>>>>> particular the setting of DISASM_INIT_STYLED (although that's supposed to be
>>>>> automatically configured by tools/objtool/Makefile).
>>>>
>>>>   I only came across these patches now.
>>>>
>>>>   As attractive as it may seem how is this stuff supposed to fly given that
>>>> binutils internal libraries promise no stable API to out-of-tree software.
>>>> The interfaces can change anytime, just as it is with our internals.
>>>>
>>>>   Wouldn't it make sense to improve objdump instead so as to provide the
>>>> features required?
>>>>
>>>>   Also is it actually legal to link objtool and libopcodes together, given
>>>> that they are GPLv2 and GPLv3 respectively?
>>>>
>>>>   FWIW asking as one of the binutils contributors and port maintainers.
>>>>
>>>
>>> After some more digging I found that the version of binutils installed in
>>> the system determines if the build error is seen or not. So I can have
>>> a toolchain with the latest binutils version, but the build still fails if
>>> the binutils version installed in the system is too old. 2.38 (as in
>>> Ubuntu 22.04) is too old since it does not define 'enum disassembler_style'
>>> in dis-asm.h. As far as I can see that enum was only introduced with
>>> binutils 2.39.
>>>
>>> Now the problem is that DISASM_INIT_STYLED is evaluated with
>>> tools/build/feature/test-disassembler-init-styled.c, which checks for
>>> the existence of struct disassemble_info (not the enum). AFAICS that
>>> structure was introduced with binutils-2_18.
>>>
>>> Unless my analysis is wrong that means that Linux will now fail to build
>>> on systems with binutils 2.18 ... 2.38 installed.
>>
>>
>> test-disassembler-init-styled.c tests that init_disassemble_info() has four
>> arguments. If this fails then this means that it has only three args and in
>> that case enum disassembler_style is not defined, and the build should be done
>> without defining DISASM_INIT_STYLED.
>>
>> init_disassemble_info() was changed from 3 args to 4 args by the following
>> binutils change, and enum disassembler_style was introduced at the same time:
>>
>>    https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=60a3da00bd5407f07
>>
>> This change has caused the Linux build to fail, and this was fixed by commit
>> a45b3d6926231 ("tools include: add dis-asm-compat.h to handle version differences")
>> which introduced dis-asm-compat.h
>>
>> Can you check that init_disassemble_info() is declared with only 3 arguments
>> in your dis-asm.h file? (/usr/include/dis-asm.h).
>>
>> dis-asm.h should either:
>>
>> - declare init_disassemble_info() with 3 args and not define enum disassembler_style
>>
>> or
>>
>> - declare init_disassemble_info() with 4 args and define enum disassembler_style
>>
> 
> Thanks for the clarification.
> 
> Here is the declaration:
> 
> /* Method to initialize a disassemble_info struct.  This should be
>     called by all applications creating such a struct.  */
> extern void init_disassemble_info (struct disassemble_info *dinfo, void *stream,
>                                     fprintf_ftype fprintf_func);
> 
> So it has three arguments, but DISASM_INIT_STYLED is defined anyway.
> 
> I think I found the problem: not even "make mrproper" or "make distclean" deletes
> ./tools/objtool/feature/test-disassembler-init-styled.bin, and the file existed
> in my tree. So DISASM_INIT_STYLED just ended up being defined until I deleted
> the file manually.
> 
> This condition also happens in my build system. I have not been able to re-create
> the situation where the .bin file exists but shouldn't, but it somehow does happen.
> 

That's weird because the "clean" rule in tools/objtool/Makefile should remove the
entire tools/objtool/feature directory:

$ cat tools/objtool/Makefile
...
clean: $(LIBSUBCMD)-clean
	$(call QUIET_CLEAN, objtool) $(RM) $(OBJTOOL)
	$(Q)find $(OUTPUT) -name '*.o' -delete -o -name '\.*.cmd' -delete -o -name '\.*.d' -delete
	$(Q)$(RM) $(OUTPUT)arch/x86/lib/cpu-feature-names.c $(OUTPUT)fixdep
	$(Q)$(RM) $(OUTPUT)arch/x86/lib/inat-tables.c $(OUTPUT)fixdep
	$(Q)$(RM) -- $(OUTPUT)FEATURE-DUMP.objtool
	$(Q)$(RM) -r -- $(OUTPUT)feature

see $(Q)$(RM) -r -- $(OUTPUT)feature

alex.