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

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

[Martin Storsjö]

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(-)

diff --git a/configure b/configure
index 534b443f7d..98a3b3814f 100755
--- a/configure
+++ b/configure
@@ -5127,7 +5127,10 @@ probe_cc(){
     elif $_cc -nologo- 2>&1 | grep -q Microsoft || { $_cc -v 2>&1 | grep -q clang && $_cc -? > /dev/null 2>&1; }; then
         _type=msvc
         if $_cc -nologo- 2>&1 | grep -q Microsoft; then
-            _ident=$($_cc 2>&1 | head -n1 | tr -d '\r')
+            # The version number is printed on the first line on stderr, stdout
+            # gets the usage instructions. Only include stderr, to avoid
+            # potential ordering race conditions.
+            _ident=$($_cc 2>&1 >/dev/null | head -n1 | tr -d '\r')
         else
             _ident=$($_cc --version 2>/dev/null | head -n1 | tr -d '\r')
         fi
-- 
2.43.0

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

[Martin Storsjö]

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.

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

[Timo Rothenpieler]

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

[Hendrik Leppkes]

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

[Kacper Michajlow]

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)

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.

btw. running cl.exe 3 times to just get its name is interesting :)

- Kacper
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