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[104.199.75.203]) by smtp.gmail.com with ESMTPSA id z8sm13066080wmg.17.2020.12.07.03.00.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 07 Dec 2020 03:00:17 -0800 (PST) Date: Mon, 7 Dec 2020 11:00:13 +0000 From: Brendan Jackman To: Andrii Nakryiko Cc: bpf , Alexei Starovoitov , Yonghong Song , Daniel Borkmann , KP Singh , Florent Revest , open list , Jann Horn Subject: Re: [PATCH bpf-next v3 12/14] bpf: Pull tools/build/feature biz into selftests Makefile Message-ID: References: <20201203160245.1014867-1-jackmanb@google.com> <20201203160245.1014867-13-jackmanb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 04, 2020 at 11:00:24AM -0800, Andrii Nakryiko wrote: > On Fri, Dec 4, 2020 at 1:41 AM Brendan Jackman wrote: > > > > On Thu, Dec 03, 2020 at 01:01:27PM -0800, Andrii Nakryiko wrote: > > > On Thu, Dec 3, 2020 at 8:07 AM Brendan Jackman wrote: > > > > > > > > This is somewhat cargo-culted from the libbpf build. It will be used > > > > in a subsequent patch to query for Clang BPF atomics support. > > > > > > > > Change-Id: I9318a1702170eb752acced35acbb33f45126c44c > > > > > > Haven't seen this before. What's this Change-Id business? > > > > Argh, apologies. Looks like it's time for me to adopt a less error-prone > > workflow for sending patches. > > > > (This is noise from Gerrit, which we sometimes use for internal reviews) > > > > > > Signed-off-by: Brendan Jackman > > > > --- > > > > tools/testing/selftests/bpf/.gitignore | 1 + > > > > tools/testing/selftests/bpf/Makefile | 38 ++++++++++++++++++++++++++ > > > > 2 files changed, 39 insertions(+) > > > > > > All this just to detect the support for clang atomics?... Let's not > > > pull in the entire feature-detection framework unnecessarily, > > > selftests Makefile is complicated enough without that. > > > > Then the test build would break for people who haven't updated Clang. > > Is that acceptable? > > > > I'm aware of cases where you need to be on a pretty fresh Clang for > > tests to _pass_ so maybe it's fine. > > I didn't mean to drop any detection of this new feature. I just didn't > want a new dependency on tools' feature probing framework. See > IS_LITTLE_ENDIAN and get_sys_includes, we already have various feature > detection-like stuff in there. So we can do this with a one-liner. I > just want to keep it simple. Thanks. Ah right gotcha. Then yeah I think we can do this: BPF_ATOMICS_SUPPORTED = $(shell \ echo "int x = 0; int foo(void) { return __sync_val_compare_and_swap(&x, 1, 2); }" \ | $(CLANG) -x cpp-output -S -target bpf -mcpu=v3 - -o /dev/null && echo 1 || echo 0)