linux-kernel - [PATCH v2] perf build: Warn for BPF skeletons if endian mismatches

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Message-Id: <20230410160905.3052640-1-irogers@google.com>
Date:   Mon, 10 Apr 2023 09:09:05 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andrii Nakryiko <andrii@...nel.org>
Subject: [PATCH v2] perf build: Warn for BPF skeletons if endian mismatches

Done as a warning as I'm not fully confident of the test's robustness
of comparing the macro definition of __BYTE_ORDER__.

Signed-off-by: Ian Rogers <irogers@...gle.com>

v2. Is a rebase following patch 1 being merged.
---
 tools/perf/Makefile.config | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
index 16bea51f0bcd..71442c54c25f 100644
--- a/tools/perf/Makefile.config
+++ b/tools/perf/Makefile.config
@@ -663,14 +663,17 @@ ifndef NO_BPF_SKEL
   $(call feature_check,clang-bpf-co-re)
   ifeq ($(feature-clang-bpf-co-re), 0)
     dummy := $(error: ERROR: BPF skeletons unsupported. clang too old/not installed or build with NO_BPF_SKEL=1.)
-  else
-    ifeq ($(filter -DHAVE_LIBBPF_SUPPORT, $(CFLAGS)),)
-      dummy := $(error: ERROR: BPF skeletons unsupported. BPF skeleton support requires libbpf or build with NO_BPF_SKEL=1.)
-    else
-      $(call detected,CONFIG_PERF_BPF_SKEL)
-      CFLAGS += -DHAVE_BPF_SKEL
-    endif
   endif
+  ifeq ($(filter -DHAVE_LIBBPF_SUPPORT, $(CFLAGS)),)
+    dummy := $(error: ERROR: BPF skeletons unsupported. BPF skeleton support requires libbpf or build with NO_BPF_SKEL=1.)
+  endif
+  host_byte_order=$(echo ""|$(HOSTCC) -dM -E -|grep __BYTE_ORDER__)
+  target_byte_order=$(echo ""|$(CC) -dM -E -|grep __BYTE_ORDER__)
+  ifneq ($(host_byte_order), $(target_byte_order))
+    $(warning Possibly mismatched host and target endianness may break BPF skeletons)
+  endif
+  $(call detected,CONFIG_PERF_BPF_SKEL)
+  CFLAGS += -DHAVE_BPF_SKEL
 endif
 
 dwarf-post-unwind := 1
-- 
2.40.0.577.gac1e443424-goog