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

[Alexander Strasser via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

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Hi Martin!

On 2025-06-21 13:37 +0300, Martin Storsjö wrote:
> > On 21. Jun 2025, at 12.20, Alexander Strasser via ffmpeg-devel <ffmpeg-devel@ffmpeg.org> wrote:
> > 
> > 
> > On 2025-06-21 00:03 +0200, 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:
> >>>> 
> >>>> 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.
> > 
> > I think making sure to only use the first line that starts with
> > Microsoft is more robust; there could be (in the future) more lines
> > that start with Microsoft.
> > 
> >> btw. running cl.exe 3 times to just get its name is interesting :)
> > 
> > Yes, so that as well. Could be optimized, but is probably not so
> > relevant in total.
> > 
> > I propose the attached patch.
> > 
> > 
> >  Alexander
> > <0001-configure-Fix-a-regression-when-probing-link.exe.patch>
> 
> Thanks, this patch looks good to me, feel free to push! (And I can push it later today if nobody else does it before that.)
> 
> If you want to, one can also extend the commit message further to say more explicitly, that 45a30e03613a3c63d74a40f7ac86ce28dce14ff8 caused configure to hang in some configurations, which this fixes.

I have attached an updated version. Hope you like the commit message
better.

I can push it tomorrow or you can do earlier.


Thanks,
  Alexander

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From d71f2bd07a9a723158fb1ec59ec7398fe7aee577 Mon Sep 17 00:00:00 2001
From: Alexander Strasser <eclipse7@gmx.net>
Date: Sat, 21 Jun 2025 11:13:22 +0200
Subject: [PATCH] configure: Fix a regression when probing link.exe

The version ident is printed on stdout for link.exe and redirecting
stdout to /dev/null will cause the output of link.exe to be paged.

This caused configure to hang for some configurations and by
extension some FATE clients. You might want to check if you run
affected configurations automated in FATE clients or similar setups.

Fixes: 45a30e03613a3c63d74a40f7ac86ce28dce14ff8
---
 configure | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/configure b/configure
index 708ecd9025..ce027d3845 100755
--- a/configure
+++ b/configure
@@ -5130,10 +5130,9 @@ 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 $_cc -nologo- 2>&1 | grep -q ^Microsoft; then
-            # The version number is printed on the first line on stderr, stdout
-            # gets the usage instructions. Only include stderr, to avoid
-            # potential ordering race conditions.
-            _ident=$($_cc 2>&1 >/dev/null | head -n1 | tr -d '\r')
+            # Depending on the tool (cl.exe or link.exe), the version number
+            # is printed on the first line of stderr or stdout
+            _ident=$($_cc 2>&1 | grep ^Microsoft | head -n1 | tr -d '\r')
         else
             _ident=$($_cc --version 2>/dev/null | head -n1 | tr -d '\r')
         fi
-- 


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