[PATCH 08/10] mfd: atmel-smc: Silence comparison of unsigned expression < 0 is always false warning (W=1)
GENMASK and it's callees conduct checking to ensure the passed parameters are valid. One of those checks is for '< 0'. So if an unsigned value is passed, in an invalid comparison takes place.
Judging from the current code, it looks as though 'unsigned int' is the correct type to use, so simply cast these small values with no chance of being false negative to signed int for comparison/error checking purposes.
Squashes the following W=1 warnings:
In file included from /home/lee/projects/linux/kernel/include/linux/bits.h:23, from /home/lee/projects/linux/kernel/include/linux/bitops.h:5, from /home/lee/projects/linux/kernel/include/linux/kernel.h:12, from /home/lee/projects/linux/kernel/include/linux/mfd/syscon/atmel-smc.h:14, from /home/lee/projects/linux/kernel/drivers/mfd/atmel-smc.c:11: /home/lee/projects/linux/kernel/drivers/mfd/atmel-smc.c: In function ‘atmel_smc_cs_encode_ncycles’: /home/lee/projects/linux/kernel/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))) | ^ /home/lee/projects/linux/kernel/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)); }))) | ^ /home/lee/projects/linux/kernel/include/linux/bits.h:39:3: note: in expansion of macro ‘GENMASK_INPUT_CHECK’ 39 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l)) | ^~~~~~~~~~~~~~~~~~~ /home/lee/projects/linux/kernel/drivers/mfd/atmel-smc.c:49:25: note: in expansion of macro ‘GENMASK’ 49 | unsigned int lsbmask = GENMASK(msbpos - 1, 0); | ^~~~~~~ /home/lee/projects/linux/kernel/include/linux/bits.h:26:40: warning: comparison of unsigned expression < 0 is always false [-Wtype-limits] 26 | __builtin_constant_p((l) > (h)), (l) > (h), 0))) | ^ /home/lee/projects/linux/kernel/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)); }))) | ^ /home/lee/projects/linux/kernel/include/linux/bits.h:39:3: note: in expansion of macro ‘GENMASK_INPUT_CHECK’ 39 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l)) | ^~~~~~~~~~~~~~~~~~~
Cc: stable@vger.kernel.org Cc: Nicolas Ferre nicolas.ferre@microchip.com Cc: Alexandre Belloni alexandre.belloni@bootlin.com Cc: Ludovic Desroches ludovic.desroches@microchip.com Cc: Boris Brezillon boris.brezillon@free-electrons.com Signed-off-by: Lee Jones lee.jones@linaro.org --- drivers/mfd/atmel-smc.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/mfd/atmel-smc.c b/drivers/mfd/atmel-smc.c index 1fa2ec950e7df..17bbe9d1fa740 100644 --- a/drivers/mfd/atmel-smc.c +++ b/drivers/mfd/atmel-smc.c @@ -46,8 +46,8 @@ static int atmel_smc_cs_encode_ncycles(unsigned int ncycles, unsigned int msbfactor, unsigned int *encodedval) { - unsigned int lsbmask = GENMASK(msbpos - 1, 0); - unsigned int msbmask = GENMASK(msbwidth - 1, 0); + unsigned int lsbmask = GENMASK((int)msbpos - 1, 0); + unsigned int msbmask = GENMASK((int)msbwidth - 1, 0); unsigned int msb, lsb; int ret = 0;
Hi,
On 25/06/2020 07:46:17+0100, Lee Jones wrote:
GENMASK and it's callees conduct checking to ensure the passed parameters are valid. One of those checks is for '< 0'. So if an unsigned value is passed, in an invalid comparison takes place.
Judging from the current code, it looks as though 'unsigned int' is the correct type to use, so simply cast these small values with no chance of being false negative to signed int for comparison/error checking purposes.
I've been thinking about that one but shouldn't the proper fix be in GENMASK? My understanding is that this happens because l is 0 and I don't think GENMASK would ever expect negative number. What about simply checking that h != l when l is 0?
Squashes the following W=1 warnings:
In file included from /home/lee/projects/linux/kernel/include/linux/bits.h:23, from /home/lee/projects/linux/kernel/include/linux/bitops.h:5, from /home/lee/projects/linux/kernel/include/linux/kernel.h:12, from /home/lee/projects/linux/kernel/include/linux/mfd/syscon/atmel-smc.h:14, from /home/lee/projects/linux/kernel/drivers/mfd/atmel-smc.c:11: /home/lee/projects/linux/kernel/drivers/mfd/atmel-smc.c: In function ‘atmel_smc_cs_encode_ncycles’: /home/lee/projects/linux/kernel/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))) | ^ /home/lee/projects/linux/kernel/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)); }))) | ^ /home/lee/projects/linux/kernel/include/linux/bits.h:39:3: note: in expansion of macro ‘GENMASK_INPUT_CHECK’ 39 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l)) | ^~~~~~~~~~~~~~~~~~~ /home/lee/projects/linux/kernel/drivers/mfd/atmel-smc.c:49:25: note: in expansion of macro ‘GENMASK’ 49 | unsigned int lsbmask = GENMASK(msbpos - 1, 0); | ^~~~~~~ /home/lee/projects/linux/kernel/include/linux/bits.h:26:40: warning: comparison of unsigned expression < 0 is always false [-Wtype-limits] 26 | __builtin_constant_p((l) > (h)), (l) > (h), 0))) | ^ /home/lee/projects/linux/kernel/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)); }))) | ^ /home/lee/projects/linux/kernel/include/linux/bits.h:39:3: note: in expansion of macro ‘GENMASK_INPUT_CHECK’ 39 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l)) | ^~~~~~~~~~~~~~~~~~~
Cc: stable@vger.kernel.org Cc: Nicolas Ferre nicolas.ferre@microchip.com Cc: Alexandre Belloni alexandre.belloni@bootlin.com Cc: Ludovic Desroches ludovic.desroches@microchip.com Cc: Boris Brezillon boris.brezillon@free-electrons.com Signed-off-by: Lee Jones lee.jones@linaro.org
drivers/mfd/atmel-smc.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/mfd/atmel-smc.c b/drivers/mfd/atmel-smc.c index 1fa2ec950e7df..17bbe9d1fa740 100644 --- a/drivers/mfd/atmel-smc.c +++ b/drivers/mfd/atmel-smc.c @@ -46,8 +46,8 @@ static int atmel_smc_cs_encode_ncycles(unsigned int ncycles, unsigned int msbfactor, unsigned int *encodedval) {
- unsigned int lsbmask = GENMASK(msbpos - 1, 0);
- unsigned int msbmask = GENMASK(msbwidth - 1, 0);
- unsigned int lsbmask = GENMASK((int)msbpos - 1, 0);
- unsigned int msbmask = GENMASK((int)msbwidth - 1, 0); unsigned int msb, lsb; int ret = 0;
2.25.1
On Fri, 26 Jun 2020, Alexandre Belloni wrote:
Hi,
On 25/06/2020 07:46:17+0100, Lee Jones wrote:
GENMASK and it's callees conduct checking to ensure the passed parameters are valid. One of those checks is for '< 0'. So if an unsigned value is passed, in an invalid comparison takes place.
Judging from the current code, it looks as though 'unsigned int' is the correct type to use, so simply cast these small values with no chance of being false negative to signed int for comparison/error checking purposes.
I've been thinking about that one but shouldn't the proper fix be in GENMASK? My understanding is that this happens because l is 0 and I don't think GENMASK would ever expect negative number. What about simply checking that h != l when l is 0?
Looks like Rikard Falkeborn recently submitted a patch to 'fix' this issue. However, Linus slammed it, decrying that it's the warning that's wrong, not the code. Looks like the type-limits warning might be getting downgraded to W=2 instead (although I don't see a patch yet).
I'm going to drop this patch.
linux-stable-mirror@lists.linaro.org
-
Alexandre Belloni -
Lee Jones