Re: [PATCH v1] perf build: Revert "enable -fno-strict-aliasing"

[Peter Zijlstra <peterz@infradead.org>]

On Thu, Sep 04, 2025 at 10:44:30AM -0700, Ian Rogers wrote:
> This reverts commit 55a18d2f3ff7 ("perf build: enable
> -fno-strict-aliasing"). With (get|put)_unaligned_* using memcpy
> -fno-strict-aliasing is no longer necessary as memcpys are assumed to
> possibly alias.

I don't think this is a good idea. Much of tools/ includes kernel
headers and various kernel code, all of which is written in the
understanding that this (often called broken) C language feature does
not exist.

As such, I would strongly suggest all of tools is built with
-fno-strict-aliasing.

> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
> This patch needs:
> https://lore.kernel.org/lkml/20250722215754.672330-1-irogers@google.com/
> which have been merged into the tip timers/vdso branch.
> ---
>  tools/perf/Makefile.config | 4 ----
>  1 file changed, 4 deletions(-)
> 
> diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
> index 5a5832ee7b53..306b8334b788 100644
> --- a/tools/perf/Makefile.config
> +++ b/tools/perf/Makefile.config
> @@ -19,10 +19,6 @@ 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
> -- 
> 2.51.0.355.g5224444f11-goog
>