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

From: Hendrik Leppkes <h.leppkes-at-gmail.com@ffmpeg.org>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH] configure: Make MSVC version grabbing more robust
Date: Fri, 20 Jun 2025 22:26:08 +0200
Message-ID: <CA+anqdxSr7ZPPBybH_vtbgjxQ5Q0bqG-OMuytfmTsZac6aht6g@mail.gmail.com> (raw)
In-Reply-To: <e36b3145-6caa-4a09-8d18-c484ef0a5d80@rothenpieler.org>

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)

- Hendrik
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