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Date: Wed, 30 Sep 2020 10:28:33 +0100 From: Lorenz Bauer <lmb@...udflare.com> To: Alexei Starovoitov <alexei.starovoitov@...il.com> Cc: Martin KaFai Lau <kafai@...com>, Shuah Khan <shuah@...nel.org>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, kernel-team <kernel-team@...udflare.com>, "open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>, Network Development <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH bpf-next v2 2/4] selftests: bpf: Add helper to compare socket cookies On Tue, 29 Sep 2020 at 16:48, Alexei Starovoitov <alexei.starovoitov@...il.com> wrote: ... > There was a warning. I noticed it while applying and fixed it up. > Lorenz, please upgrade your compiler. This is not the first time such > warning has been missed. I tried reproducing this on latest bpf-next (b0efc216f577997) with gcc 9.3.0 by removing the initialization of duration: make: Entering directory '/home/lorenz/dev/bpf-next/tools/testing/selftests/bpf' TEST-OBJ [test_progs] sockmap_basic.test.o TEST-HDR [test_progs] tests.h EXT-OBJ [test_progs] test_progs.o EXT-OBJ [test_progs] cgroup_helpers.o EXT-OBJ [test_progs] trace_helpers.o EXT-OBJ [test_progs] network_helpers.o EXT-OBJ [test_progs] testing_helpers.o BINARY test_progs make: Leaving directory '/home/lorenz/dev/bpf-next/tools/testing/selftests/bpf' So, gcc doesn't issue a warning. Jakub did the following little experiment: jkbs@...d ~/tmp $ cat warning.c #include <stdio.h> int main(void) { int duration; fprintf(stdout, "%d", duration); return 0; } jkbs@...d ~/tmp $ gcc -Wall -o /dev/null warning.c warning.c: In function ‘main’: warning.c:7:2: warning: ‘duration’ is used uninitialized in this function [-Wuninitialized] 7 | fprintf(stdout, "%d", duration); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The simple case seems to work. However, adding the macro breaks things: jkbs@...d ~/tmp $ cat warning.c #include <stdio.h> #define _CHECK(duration) \ ({ \ fprintf(stdout, "%d", duration); \ }) #define CHECK() _CHECK(duration) int main(void) { int duration; CHECK(); return 0; } jkbs@...d ~/tmp $ gcc -Wall -o /dev/null warning.c jkbs@...d ~/tmp $ Maybe this is https://gcc.gnu.org/bugzilla/show_bug.cgi?id=18501 ? The problem is still there on gcc 10. Compiling test_progs with clang does issue a warning FWIW, but it seems like other things break when doing that. -- Lorenz Bauer | Systems Engineer 6th Floor, County Hall/The Riverside Building, SE1 7PB, UK www.cloudflare.com
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