From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:60187) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bADfD-0003RO-MC for qemu-devel@nongnu.org; Tue, 07 Jun 2016 05:51:12 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bADf9-0000mW-FG for qemu-devel@nongnu.org; Tue, 07 Jun 2016 05:51:10 -0400 Received: from mx1.redhat.com ([209.132.183.28]:40264) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bADf9-0000mK-9a for qemu-devel@nongnu.org; Tue, 07 Jun 2016 05:51:07 -0400 Date: Tue, 7 Jun 2016 10:51:02 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20160607095102.GB2257@work-vm> References: <1465234520-11160-1-git-send-email-pbonzini@redhat.com> <20160606192219.GB2258@work-vm> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Subject: Re: [Qemu-devel] [PULL 00/11] Misc changes for 2016-06-06 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Maydell Cc: Paolo Bonzini , QEMU Developers * Peter Maydell (peter.maydell@linaro.org) wrote: > On 6 June 2016 at 20:22, Dr. David Alan Gilbert wrote: > > Sigh I see; so the configure test is run with a different set of compiler > > options than the main compiles? How is any configure test supposed to > > check that it's got a sane configuration? > > I wasn't quite right -- we do run configure tests with ccache, we just > force it to not read the cache. So I think your problem is just that > your configure test doesn't fail when run under ccache, even though the > main cutils.c compile does: > > $ cat /tmp/zz9.c > #pragma GCC push_options > #pragma GCC target("avx2") > #include > #include > > static int bar(void *a) { > return _mm256_movemask_epi8(_mm256_cmpeq_epi8(*(__m256i *)a, (__m256i){0})); > } > static void *bar_ifunc(void) {return (void*) bar;} > int foo(void *a) __attribute__((ifunc("bar_ifunc"))); > int main(int argc, char *argv[]) { return foo(argv[0]);} > $ ccache gcc -g -Wall -o /tmp/zz9 /tmp/zz9.c > > This seems to be because to get the compile failure you have > to be doing a .c to .o compile: > The difference is because ccache doesn't intercept .c-to-executable > compiles, so they go straight to real gcc and don't have -save-temps, > but it does intercept a .c-to-.o compile, which thus does get -save-temps > and so hits the gcc bug. > > TLDR: if you make your configure test use compile_object it ought to > correctly detect that AVX2 doesn't work for this gcc+ccache combo. Does the following (on top of the existing patch) fix it for you: diff --git a/configure b/configure index 6449e65..65e603c 100755 --- a/configure +++ b/configure @@ -1793,8 +1793,8 @@ static void *bar_ifunc(void) {return (void*) bar;} int foo(void *a) __attribute__((ifunc("bar_ifunc"))); int main(int argc, char *argv[]) { return foo(argv[0]);} EOF -if compile_prog "" ; then - if readelf --syms $TMPE |grep "IFUNC.*foo" >/dev/null 2>&1; then +if compile_object "" ; then + if readelf --syms $TMPO |grep "IFUNC.*foo" >/dev/null 2>&1; then avx2_opt="yes" fi fi Dave > > thanks > -- PMM -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK