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[158.174.22.22]) by smtp.gmail.com with ESMTPSA id c7sm794800ljj.109.2020.06.03.15.03.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 03 Jun 2020 15:03:45 -0700 (PDT) From: Rikard Falkeborn To: rikard.falkeborn@gmail.com Cc: akpm@linux-foundation.org, andy.shevchenko@gmail.com, arnd@arndb.de, emil.l.velikov@gmail.com, keescook@chromium.org, linus.walleij@linaro.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, syednwaris@gmail.com, vilhelm.gray@gmail.com, yamada.masahiro@socionext.com, kbuild test robot Subject: [PATCH] linux/bits.h: fix unsigned less than zero warnings Date: Thu, 4 Jun 2020 00:02:26 +0200 Message-Id: <20200603220226.916269-1-rikard.falkeborn@gmail.com> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20200603215314.GA916134@rikard> References: <20200603215314.GA916134@rikard> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When calling the GENMASK and GENMASK_ULL macros with zero lower bit and an unsigned unknown high bit, some gcc versions warn due to the comparisons of the high and low bit in GENMASK_INPUT_CHECK. To silence the warnings, cast the inputs to int before doing the comparisons. The only valid inputs to GENMASK() and GENMASK_ULL() are are 0 to 31 or 63. Anything outside this is undefined due to the shifts in GENMASK()/GENMASK_ULL(). Therefore, casting the inputs to int do not change the values for valid known inputs. For unknown values, the check does not change anything since it's a compile-time check only. As an example of the warning, kindly reported by the kbuild test robot: from drivers/mfd/atmel-smc.c:11: drivers/mfd/atmel-smc.c: In function 'atmel_smc_cs_encode_ncycles': include/linux/bits.h:26:28: warning: comparison of unsigned expression < 0 is always false [-Wtype-limits] 26 | __builtin_constant_p((l) > (h)), (l) > (h), 0))) | ^ include/linux/build_bug.h:16:62: note: in definition of macro 'BUILD_BUG_ON_ZERO' 16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); }))) | ^ include/linux/bits.h:39:3: note: in expansion of macro 'GENMASK_INPUT_CHECK' 39 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l)) | ^~~~~~~~~~~~~~~~~~~ >> drivers/mfd/atmel-smc.c:49:25: note: in expansion of macro 'GENMASK' 49 | unsigned int lsbmask = GENMASK(msbpos - 1, 0); | ^~~~~~~ Fixes: 295bcca84916 ("linux/bits.h: add compile time sanity check of GENMASK inputs") Reported-by: kbuild test robot Reported-by: Emil Velikov Reported-by: Syed Nayyar Waris Signed-off-by: Rikard Falkeborn --- include/linux/bits.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/include/linux/bits.h b/include/linux/bits.h index 4671fbf28842..293d1ee71a48 100644 --- a/include/linux/bits.h +++ b/include/linux/bits.h @@ -21,9 +21,10 @@ #if !defined(__ASSEMBLY__) && \ (!defined(CONFIG_CC_IS_GCC) || CONFIG_GCC_VERSION >= 49000) #include +/* Avoid Wtype-limits warnings by casting the inputs to int */ #define GENMASK_INPUT_CHECK(h, l) \ (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \ - __builtin_constant_p((l) > (h)), (l) > (h), 0))) + __builtin_constant_p((int)(l) > (int)(h)), (int)(l) > (int)(h), 0))) #else /* * BUILD_BUG_ON_ZERO is not available in h files included from asm files, -- 2.27.0