linux-kernel - Re: [PATCH 2/2] perf symbols: Fix HAVE_LIBBFD_BUILDID

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Message-ID: <70bd9eea-905a-4fa9-8265-f84ab9894b12@linaro.org>
Date: Thu, 4 Sep 2025 09:13:16 +0100
From: James Clark <james.clark@...aro.org>
To: Ian Rogers <irogers@...gle.com>, Sam James <sam@...too.org>,
 rbernon@...eweavers.com
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Jiri Olsa <jolsa@...nel.org>, Adrian Hunter <adrian.hunter@...el.com>,
 Leo Yan <leo.yan@....com>, linux-perf-users@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] perf symbols: Fix HAVE_LIBBFD_BUILDID_SUPPORT build



On 03/09/2025 5:07 pm, Ian Rogers wrote:
> On Wed, Sep 3, 2025 at 8:15 AM James Clark <james.clark@...aro.org> wrote:
>>
>> read_build_id() now has a blocking argument, but libbfd uses fopen()
>> internally which doesn't support O_NONBLOCK. Fix the build by adding the
>> argument and ignoring it:
>>
>>    util/symbol-elf.c:964:8: error: too many arguments to function ‘read_build_id’
>>      964 |  err = read_build_id(filename, bid, block);
>>
>> Fixes: 2c369d91d093 ("perf symbol: Add blocking argument to filename__read_build_id")
>> Signed-off-by: James Clark <james.clark@...aro.org>
> 
> Libbfd should go away:
> https://lore.kernel.org/lkml/20250823003216.733941-14-irogers@google.com/
> but I can imagine that currently this is hit in a build test - sorry
> for missing that and thanks for the fix!
> 

Yeah just one of the build tests, I'm not actually using it.

Remi are you still using this? To be fair the addition for PE support is 
fairly recent and even includes a binary for testing it so I'm not sure 
if we should be so quick to remove it.

Having said that, it is a bit weird that it's basically not compiled in 
anywhere. And the current array of supported disassemblers etc is 
completely bewildering and hard to maintain.

> We should probably honor the blocking argument (use fdopen) as the
> probe perf tests will invoke perf record system wide with data pages
> and predictably hang on this for files like mmap-ed in sound devices.
> That said, maybe this hanging will serve as an indication not to use
> the deprecated libbfd code. From the sounds of things this will break
> gentoo :-(
> https://lore.kernel.org/lkml/87ldnacz33.fsf@gentoo.org/

If it's just going to be a test issue we can probably live with it. I'm 
not sure how to honor the blocking argument, I did have a look into 
libbfd but it didn't seem possible after looking for a few minutes. 
Probably not worth spending any more time on it until we decide whether 
it's staying or not.

> 
> Thanks,
> Ian
> 
>> ---
>>   tools/perf/util/symbol-elf.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
>> index 033c79231a54..e0d6ff7d0acf 100644
>> --- a/tools/perf/util/symbol-elf.c
>> +++ b/tools/perf/util/symbol-elf.c
>> @@ -873,7 +873,8 @@ static int elf_read_build_id(Elf *elf, void *bf, size_t size)
>>
>>   #ifdef HAVE_LIBBFD_BUILDID_SUPPORT
>>
>> -static int read_build_id(const char *filename, struct build_id *bid)
>> +static int read_build_id(const char *filename, struct build_id *bid,
>> +                        bool block __maybe_unused)
>>   {
>>          size_t size = sizeof(bid->data);
>>          int err = -1;
>>
>> --
>> 2.34.1
>>