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Date:   Tue, 16 Jun 2020 10:42:22 -0700
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     Marco Elver <elver@google.com>
Cc:     linux-kernel@vger.kernel.org, josh@joshtriplett.org,
        rostedt@goodmis.org, mathieu.desnoyers@efficios.com,
        jiangshanlai@gmail.com, shuah@kernel.org, rcu@vger.kernel.org,
        linux-kselftest@vger.kernel.org
Subject: Re: [PATCH] torture: Pass --kmake-arg to all make invocations
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 <20200616164202.GA208325@google.com>
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On Tue, Jun 16, 2020 at 06:42:02PM +0200, Marco Elver wrote:
> On Tue, Jun 16 2020 at 09:05AM -0700, Paul E. McKenney wrote:
> 
> > On Tue, Jun 16, 2020 at 11:49:24AM +0200, Marco Elver wrote:
> > > We need to pass the arguments provided to --kmake-arg to all make
> > > invocations. In particular, the make invocations generating the configs
> > > need to see the final make arguments, e.g. if config variables depend on
> > > particular variables that are passed to make.
> > > 
> > > For example, when using '--kcsan --kmake-arg CC=clang-11', we would lose
> > > CONFIG_KCSAN=y due to 'make oldconfig' not seeing that we want to use a
> > > compiler that supports KCSAN.
> > > 
> > > Signed-off-by: Marco Elver <elver@google.com>
> > 
> > Queued and pushed, thank you!
> > 
> > Would the following patch make sense, at least until such time
> > as some other compiler supports KCSAN?
> > 
> > 							Thanx, Paul
> > 
> > ------------------------------------------------------------------------
> > 
> > commit 88bcaa730b6d40ddf69b09ed6f0a14803d087d99
> > Author: Paul E. McKenney <paulmck@kernel.org>
> > Date:   Tue Jun 16 09:02:34 2020 -0700
> > 
> >     torture: Make --kcsan default to using Clang 11
> >     
> >     Currently, Clang 11 is the only compiler that can support KCSAN.
> >     Therefore, as a convenience to the KCSAN user, this commit causes
> >     --kcsan to specify Clang 11 unless a "CC=" argument was already
> >     specified via the --kmake-arg argument.
> 
> As soon as more compilers support KCSAN (e.g. clang-12, etc...) we run
> the risk of actually inconveniencing ourselves more because then we
> really need to say '--kmake-arg CC=clang-1X' to not use the old
> compiler. Or revert this in time.
> 
> My command-line looks more like this right now:
> 
> 	kvm.sh ... --kmake-arg "CC="${HOME}/local/<gcc-or-clang>-11.kcsan/local/bin/<gcc-or-clang>" ...
> 
> I think the safer alternative would be to error if CONFIG_KCSAN=y is not
> in the config, and simply suggest "Did you forget to switch your
> compiler with '--kmake-arg CC=<cc-that-supports-kcsan>'?" (of course, a
> 'gcc' in $PATH that supports KCSAN would also be fine -- see below).
> Eventually, when the default compilers support KCSAN, this will resolve
> itself gracefully.
> 
> Also, I'm going to send a series later this week to re-enable GCC
> support. ;-)

OK, sounds like I should leave well enough alone, then.  ;-)

In its current state, specifying "--kcsan" without a KCSAN-capable
compiler does get you this:

:CONFIG_KCSAN=y: improperly set
:CONFIG_KCSAN_REPORT_ONCE_IN_MS=100000: improperly set
:CONFIG_KCSAN_VERBOSE=y: improperly set
:CONFIG_KCSAN_INTERRUPT_WATCHER=y: improperly set
Clean KCSAN run in /home/git/linux-rcu/tools/testing/selftests/rcutorture/res/2020.06.16-09.53.16

Which admittedly is a bit obtuse, especially that last line.  So how
about the following patch, which instead results in this?

:CONFIG_KCSAN=y: improperly set
:CONFIG_KCSAN_REPORT_ONCE_IN_MS=100000: improperly set
:CONFIG_KCSAN_VERBOSE=y: improperly set
:CONFIG_KCSAN_INTERRUPT_WATCHER=y: improperly set
Did you forget to switch your compiler with --kmake-arg CC=<cc-that-supports-kcsan>?

							Thanx, Paul

------------------------------------------------------------------------

commit f571795b1146007407851675a258b6685ea2d589
Author: Paul E. McKenney <paulmck@kernel.org>
Date:   Tue Jun 16 10:38:57 2020 -0700

    torture: Improve diagnostic for KCSAN-incapable compilers
    
    Using --kcsan when the compiler does not support KCSAN results in this:
    
    :CONFIG_KCSAN=y: improperly set
    :CONFIG_KCSAN_REPORT_ONCE_IN_MS=100000: improperly set
    :CONFIG_KCSAN_VERBOSE=y: improperly set
    :CONFIG_KCSAN_INTERRUPT_WATCHER=y: improperly set
    Clean KCSAN run in /home/git/linux-rcu/tools/testing/selftests/rcutorture/res/2020.06.16-09.53.16
    
    This is a bit obtuse, so this commit adds checks resulting in this:
    
    :CONFIG_KCSAN=y: improperly set
    :CONFIG_KCSAN_REPORT_ONCE_IN_MS=100000: improperly set
    :CONFIG_KCSAN_VERBOSE=y: improperly set
    :CONFIG_KCSAN_INTERRUPT_WATCHER=y: improperly set
    Did you forget to switch your compiler with --kmake-arg CC=<cc-that-supports-kcsan>?
    
    Suggested-by: Marco Elver <elver@google.com>
    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/tools/testing/selftests/rcutorture/bin/kvm-recheck.sh b/tools/testing/selftests/rcutorture/bin/kvm-recheck.sh
index 357899c..837643a 100755
--- a/tools/testing/selftests/rcutorture/bin/kvm-recheck.sh
+++ b/tools/testing/selftests/rcutorture/bin/kvm-recheck.sh
@@ -44,7 +44,8 @@ do
 			then
 				echo QEMU killed
 			fi
-			configcheck.sh $i/.config $i/ConfigFragment
+			configcheck.sh $i/.config $i/ConfigFragment > $T 2>&1
+			cat $T
 			if test -r $i/Make.oldconfig.err
 			then
 				cat $i/Make.oldconfig.err
@@ -73,7 +74,10 @@ do
 	done
 	if test -f "$rd/kcsan.sum"
 	then
-		if test -s "$rd/kcsan.sum"
+		if grep -q CONFIG_KCSAN=y $T
+		then
+			echo Did you forget to switch your compiler with '--kmake-arg CC=<cc-that-supports-kcsan>'?
+		elif test -s "$rd/kcsan.sum"
 		then
 			echo KCSAN summary in $rd/kcsan.sum
 		else