Re: [FFmpeg-devel] [PATCH] configure: Make MSVC version grabbing more robust

["Martin Storsjö" <martin@martin.st>]

On Sat, 21 Jun 2025, Kacper Michajlow wrote:

> On Fri, 20 Jun 2025 at 22:26, Hendrik Leppkes
> <h.leppkes-at-gmail.com@ffmpeg.org> wrote:
>>
>> On Fri, Jun 20, 2025 at 9:25 PM Timo Rothenpieler <timo@rothenpieler.org> wrote:
>> >
>> > On 19.06.2025 22:21, Martin Storsjö wrote:
>> > > On Fri, 13 Jun 2025, Martin Storsjö wrote:
>> > >
>> > >> When running plain "cl", to get the MSVC version, it prints the
>> > >> version header on stderr, while the usage instructions are printed
>> > >> on stdout. Usually, the version on stderr gets flushed first,
>> > >> so "head -n1" gets the line it expects, but some times (in particular
>> > >> when running MSVC wrapped in wine), it can get the usage line
>> > >> first.
>> > >>
>> > >> Redirect stdout to /dev/null, so we only grab the version among
>> > >> the lines printed to stderr. This should make the version number
>> > >> grabbing more robust.
>> > >>
>> > >> At least all relevant versions of MSVC seem to print this specifically
>> > >> to stderr, not stdout (so we don't risk to miss it); checked down
>> > >> to MSVC 2010.
>> > >> ---
>> > >> This should avoid the occasionally misdetected version number lines
>> > >> as seen at https://fate.ffmpeg.org/history.cgi?slot=x86_64-msvc2022-wine.
>> > >> ---
>> > >> configure | 5 ++++-
>> > >> 1 file changed, 4 insertions(+), 1 deletion(-)
>> > >
>> > > Will push.
>> >
>> > Likely this patch broke multiple fate runners in a silent way.
>> > On mine, configure simply never returns, and just sits there
>> > indefinitely, with no CPU usage or any activity whatsoever.
>> >
>> > nevcairiel confirmed seeing the same behaviour on IRC.
>> >
>> > The msys+clang builds from within the same environment work fine.
>> >
>> >
>> > Didn't verify completely if it's caused by this patch, but nothing else
>> > happened with configure since the last successful run.
>>
>> I did some digging, and it happens when probe_cc probes link.exe
>>
>> link.exe has an interactive help output (its paginated) - previously
>> piping stdout disabled the pagination automatically - but redirecting
>> it to devnull does not, and it gets stuck waiting for input.
>> Additionally, link.exe outputs the ident on stdout, so there is no
>> result on stderr (not super bad, as LD_IDENT is never used - yet)

Sorry about the breakage, and thanks for figuring out what's wrong!

It's odd that this issue didn't appear for me; perhaps it's related to 
running the MSVC tools on Linux wrapped in wine somehow?

> Instead of redirecting to devnull, we could use the same condition as
> in if. We already look for specific ident line, so no need to head.
> _ident=$($_cc -nologo- 2>&1 | grep ^Microsoft | tr -d '\r')
> should work, no? I would be happy to see a better solution, though.

That sounds like a quite reasonable solution, thanks!

// Martin
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