From: Andrew Burgess <email@example.com>
To: Andres Freund <firstname.lastname@example.org>,
Quentin Monnet <email@example.com>
Cc: open list <firstname.lastname@example.org>,
Arnaldo Carvalho de Melo <email@example.com>
Subject: Re: init_disassemble_info() signature changes causes compile failures
Date: Thu, 23 Jun 2022 10:49:51 +0100 [thread overview]
Message-ID: <firstname.lastname@example.org> (raw)
Andres Freund <email@example.com> writes:
> On 2022-06-22 23:53:58 +0100, Quentin Monnet wrote:
>> Too bad the libbfd API is changing again :/
> Yea, not great. Particularly odd that
> /* For compatibility with existing code. */
> #define INIT_DISASSEMBLE_INFO(INFO, STREAM, FPRINTF_FUNC, FPRINTF_STYLED_FUNC) \
> was changed. Leaving the "For compatibility with existing code." around,
> despite obviously not providing compatibility...
> CCed the author of that commit, maybe worth fixing?
First, massive appologies for breaking you existing code. I wasn't
aware that the libopcodes disassembler was used by anything out of
> Given that disassemble_set_printf() was added, it seems like it'd have been
> easy to not change init_disassemble_info() / INIT_DISASSEMBLE_INFO() and
> require disassemble_set_printf() to be called to get styled printf support.
When I did this work I desperately wanted to maintain the original API
as much as possible. But I couldn't figure out a way for this to work.
The problem is that we now have two classes of disassembler, those that
call the styled printf callback, and those that call the classic
When I originally did this work I did want to leave
INIT_DISASSEMBLE_INFO untouched, and provide a default styled printf
that would forward calls to the non-styled printf.
The problem I ran into is that the disassemble_info printf API is not
great. If the API had passed the disassemble_info* as one of the
arguments then this would have been trivial. But instead, we only get
passed a 'void *', which is one of the fields of disassemble_info.
As a result there's no easy way to forward calls from this imagined
default styled printf, to the actual, user supplied non-styled printf.
I did consider changing the 'void *' field from being the stream to
write to, to be the disassemble_info*, but then the non-styled printf
calls would need to be updated anyway, which would be a breaking change.
I also considered changing the 'void *' stream to be the
'disassemble_info*', then wrapping both styled and non-styled printf
calls. This would allow me to provide a default for the styled printf,
and we can pull the required information from the 'disassemble_info*',
but the problem I have now is that the wrapper functions would be a
vararg function, and the user supplied printf functions are also vararg
functions.... and I didn't know how to forward the args from my wrapper
to the user supplied functions without changing the API of the user
supplied functions to take a va_list ... which again is an API breaking
I'm aware that non of the above helps you at all, other than to say, I
didn't make this change without a little thought. But, that doesn't
mean there isn't a better way this could have been done. So, if you
have any suggestions, then I'm happy to give them a go.
Once again, sorry for the additional work this has created for you, and
if I can help at all to put this right, then please, do let me know.
Oh, and you're absolutely correct about the comment. I should have just
deleted it. Or really, I should have just deleted the macro entirely I
guess and forced everyone to call init_disassemble_info directly. Bit
late for that now though!
>> > The fix is easy enough, add a wrapper around fprintf() that conforms to the
>> > new signature.
>> > However I assume the necessary feature test and wrapper should only be added
>> > once? I don't know the kernel stuff well enough to choose the right structure
>> > here.
>> We can probably find a common header for the wrapper under
>> tools/include/. One possibility could be a new header under
>> tools/include/tools/, like for libc_compat.h. Although personally I
>> don't mind too much about redefining the wrapper several times given
>> how short it is, and because maybe some tools could redefine it anyway
>> to use colour output in the future.
> I'm more bothered by duplicating the necessary ifdefery than duplicating the
> short fprintf wrapper...
>> The feature test would better be shared, it would probably be similar
>> to what was done in the following commit to accommodate for a previous
>> change in libbfd:
> Ah, beautiful hand-rolled feature tests :)
>> > Attached is my local fix for perf. Obviously would need work to be a real
>> > solution.
>> Thanks a lot! Would you be willing to submit a patch for the feature
>> detection and wrapper?
> I'll give it a go, albeit probably not today.
> Andres Freund
next prev parent reply other threads:[~2022-06-23 9:50 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-22 18:19 init_disassemble_info() signature changes causes compile failures Andres Freund
2022-06-22 22:53 ` Quentin Monnet
2022-06-22 23:16 ` Andres Freund
2022-06-23 9:49 ` Andrew Burgess [this message]
2022-07-03 4:48 ` [PATCH v1 0/3] tools: fix compilation failure caused by init_disassemble_info API changes Andres Freund
2022-07-03 4:48 ` [PATCH v1 1/3] tools build: add feature test for " Andres Freund
2022-07-03 4:48 ` [PATCH v1 2/3] tools: add dis-asm-compat.h to centralize handling of version differences Andres Freund
2022-07-03 4:48 ` [PATCH v1 2/3] tools: introduce dis-asm.h wrapper to hide " Andres Freund
2022-07-03 4:54 ` Andres Freund
2022-07-03 4:48 ` [PATCH v1 3/3] tools: Use tools/dis-asm-compat.h to fix compilation errors with new binutils Andres Freund
2022-07-03 21:25 ` [PATCH v2 0/5] tools: fix compilation failure caused by init_disassemble_info API changes Andres Freund
2022-07-03 21:25 ` [PATCH v2 1/5] tools build: add feature test for " Andres Freund
2022-07-03 21:25 ` [PATCH v2 2/5] tools include: add dis-asm-compat.h to handle version differences Andres Freund
2022-07-05 13:44 ` Quentin Monnet
2022-07-15 19:39 ` Andres Freund
2022-07-15 19:46 ` Andres Freund
2022-07-18 8:58 ` Quentin Monnet
2022-07-03 21:25 ` [PATCH v2 3/5] tools perf: Fix compilation error with new binutils Andres Freund
2022-07-03 21:25 ` [PATCH v2 4/5] tools bpf_jit_disasm: " Andres Freund
2022-07-03 21:25 ` [PATCH v2 5/5] tools bpftool: " Andres Freund
2022-07-04 9:13 ` [PATCH v2 0/5] tools: fix compilation failure caused by init_disassemble_info API changes Jiri Olsa
2022-07-04 20:19 ` Andres Freund
2022-07-04 22:12 ` Jiri Olsa
2022-08-01 1:40 ` Andres Freund
2022-07-10 11:43 ` Sedat Dilek
2022-07-10 17:52 ` Sedat Dilek
2022-07-14 9:16 ` Sedat Dilek
2022-07-14 13:25 ` Ben Hutchings
2022-07-15 19:16 ` Andres Freund
2022-07-15 19:18 ` Ben Hutchings
2022-08-01 18:08 ` Arnaldo Carvalho de Melo
2022-07-27 15:47 ` Arnaldo Carvalho de Melo
2022-07-30 21:45 ` Andres Freund
2022-08-01 1:38 ` [PATCH v3 0/8] " Andres Freund
2022-08-01 1:38 ` [PATCH v3 1/8] tools build: Add feature test for " Andres Freund
2022-08-01 1:38 ` [PATCH v3 2/8] tools build: Don't display disassembler-four-args feature test Andres Freund
2022-08-01 18:10 ` Arnaldo Carvalho de Melo
2022-08-01 1:38 ` [PATCH v3 3/8] tools include: add dis-asm-compat.h to handle version differences Andres Freund
2022-08-01 18:05 ` Arnaldo Carvalho de Melo
2022-08-01 18:10 ` Andres Freund
2022-08-01 1:38 ` [PATCH v3 4/8] tools perf: Fix compilation error with new binutils Andres Freund
2022-08-01 1:38 ` [PATCH v3 5/8] tools bpf_jit_disasm: " Andres Freund
2022-08-01 1:38 ` [PATCH v3 6/8] tools bpf_jit_disasm: Don't display disassembler-four-args feature test Andres Freund
2022-08-01 18:27 ` Arnaldo Carvalho de Melo
2022-08-01 18:41 ` Andres Freund
2022-08-01 1:38 ` [PATCH v3 7/8] tools bpftool: Fix compilation error with new binutils Andres Freund
2022-08-01 1:38 ` [PATCH v3 8/8] tools bpftool: Don't display disassembler-four-args feature test Andres Freund
2022-08-01 18:28 ` Arnaldo Carvalho de Melo
2022-08-01 12:45 ` [PATCH v3 0/8] tools: fix compilation failure caused by init_disassemble_info API changes Arnaldo Carvalho de Melo
2022-08-01 15:15 ` Quentin Monnet
2022-08-01 18:02 ` Arnaldo Carvalho de Melo
2022-08-08 13:35 ` Daniel Borkmann
2022-08-01 19:53 ` Jiri Olsa
2022-08-01 19:12 ` Sedat Dilek
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