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Wed, 15 Apr 2026 02:43:39 -0700 (PDT) Date: Wed, 15 Apr 2026 11:43:37 +0200 From: Petr Mladek To: Tamir Duberstein Cc: Steven Rostedt , Andy Shevchenko , Rasmus Villemoes , Sergey Senozhatsky , linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel test robot Subject: Re: [PATCH v3] printf: Compile the kunit test with DISABLE_BRANCH_PROFILING DISABLE_BRANCH_PROFILING Message-ID: References: <20260406123232.3dacbe94@gandalf.local.home> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Tue 2026-04-14 12:07:59, Tamir Duberstein wrote: > On Tue, Apr 14, 2026 at 11:41 AM Petr Mladek wrote: > > > > GCC < 12.1 can miscompile printf_kunit's errptr() test when branch > > profiling is enabled. BUILD_BUG_ON(IS_ERR(PTR)) is a constant false > > expression, but CONFIG_TRACE_BRANCH_PROFILING and > > CONFIG_PROFILE_ALL_BRANCHES make the IS_ERR() path side-effectful. > > GCC's IPA splitter can then outline the cold assert arm into > > errptr.part.* and leave that clone with an unconditional > > __compiletime_assert_*() call, causing a false build failure. > > > > This started showing up after test_hashed() became a macro and moved its > > local buffer into errptr(), which changed GCC's inlining and splitting > > decisions enough to expose the compiler bug. > > > > Workaround the problem by disabling the branch profiling for > > printf_kunit.o. It is a straightforward and acceptable solution. > > > > The workaround can be removed once the minimum GCC includes commit > > 76fe49423047 ("Fix tree-optimization/101941: IPA splitting out > > function with error attribute"), which first shipped in GCC 12.1. > > > > Fixes: 9bfa52dac27a ("printf: convert test_hashed into macro") > > Reported-by: kernel test robot > > Closes: https://lore.kernel.org/oe-kbuild-all/202604030636.NqjaJvYp-lkp@intel.com/ > > Cc: stable@vger.kernel.org > > Signed-off-by: Petr Mladek > > Acked-by: Tamir Duberstein Thanks a lot for checking. JFYI, I have committed the patch into printk/linux.git, branch for-7.1-printf-kunit-build. Best Regards, Petr