linux-kernel - [PATCH v2 1/4] perf build: enable -fno-strict-aliasing

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Message-ID: <20250614044133.660848-2-ebiggers@kernel.org>
Date: Fri, 13 Jun 2025 21:41:30 -0700
From: Eric Biggers <ebiggers@...nel.org>
To: linux-perf-users@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Liang Kan <kan.liang@...ux.intel.com>,
	Yuzhuo Jing <yuzhuo@...gle.com>
Subject: [PATCH v2 1/4] perf build: enable -fno-strict-aliasing

From: Eric Biggers <ebiggers@...gle.com>

perf pulls in code from kernel headers that assumes it is being built
with -fno-strict-aliasing, namely put_unaligned_*() from
<linux/unaligned.h> which write the data using packed structs that lack
the may_alias attribute.  Enable -fno-strict-aliasing to prevent
miscompilations in sha1.c which would otherwise occur due to this issue.

Signed-off-by: Eric Biggers <ebiggers@...gle.com>
---
 tools/perf/Makefile.config | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
index d1ea7bf449647..1691b47c4694c 100644
--- a/tools/perf/Makefile.config
+++ b/tools/perf/Makefile.config
@@ -17,10 +17,14 @@ detected     = $(shell echo "$(1)=y"       >> $(OUTPUT).config-detected)
 detected_var = $(shell echo "$(1)=$($(1))" >> $(OUTPUT).config-detected)
 
 CFLAGS := $(EXTRA_CFLAGS) $(filter-out -Wnested-externs,$(EXTRA_WARNINGS))
 HOSTCFLAGS := $(filter-out -Wnested-externs,$(EXTRA_WARNINGS))
 
+# This is required because the kernel is built with this and some of the code
+# borrowed from kernel headers depends on it, e.g. put_unaligned_*().
+CFLAGS += -fno-strict-aliasing
+
 # Enabled Wthread-safety analysis for clang builds.
 ifeq ($(CC_NO_CLANG), 0)
   CFLAGS += -Wthread-safety
 endif
 
-- 
2.49.0