Commit Message
Greg KH
Oct. 24, 2022, 11:31 a.m. UTC
From: David Gow <davidgow@google.com> [ Upstream commit 6ae0632d17759852c07e2d1e0a31c728eb6ba246 ] The definition of MIN_I64 in bw_fixed.c can cause gcc to whinge about integer overflow, because it is treated as a positive value, which is then negated. The temporary positive value is not necessarily representable. This causes the following warning: ../drivers/gpu/drm/amd/amdgpu/../display/dc/dml/calcs/bw_fixed.c:30:19: warning: integer overflow in expression ‘-9223372036854775808’ of type ‘long long int’ results in ‘-9223372036854775808’ [-Woverflow] 30 | (int64_t)(-(1LL << 63)) | ^ Writing out (-MAX_I64 - 1) works instead. Signed-off-by: David Gow <davidgow@google.com> Signed-off-by: Tales Aparecida <tales.aparecida@gmail.com> Signed-off-by: Alex Deucher <alexander.deucher@amd.com> Signed-off-by: Sasha Levin <sashal@kernel.org> --- drivers/gpu/drm/amd/display/dc/calcs/bw_fixed.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
Comments
Hi! > From: David Gow <davidgow@google.com> > > [ Upstream commit 6ae0632d17759852c07e2d1e0a31c728eb6ba246 ] > > The definition of MIN_I64 in bw_fixed.c can cause gcc to whinge about > integer overflow, because it is treated as a positive value, which is > then negated. The temporary positive value is not necessarily > representable. > > This causes the following warning: > ../drivers/gpu/drm/amd/amdgpu/../display/dc/dml/calcs/bw_fixed.c:30:19: > warning: integer overflow in expression ‘-9223372036854775808’ of type > ‘long long int’ results in ‘-9223372036854775808’ [-Woverflow] > 30 | (int64_t)(-(1LL << 63)) > | ^ > > Writing out (-MAX_I64 - 1) works instead. While this probably fixes the warning, better fix would be to include limits.h which already has equivalent definitions. Thanks and best regards, Pavel > -#define MIN_I64 \ > - (int64_t)(-(1LL << 63)) > - > #define MAX_I64 \ > (int64_t)((1ULL << 63) - 1) > > +#define MIN_I64 \ > + (-MAX_I64 - 1) > + > #define FRACTIONAL_PART_MASK \ > ((1ULL << BW_FIXED_BITS_PER_FRACTIONAL_PART) - 1) > > -- > 2.35.1 > >
diff --git a/drivers/gpu/drm/amd/display/dc/calcs/bw_fixed.c b/drivers/gpu/drm/amd/display/dc/calcs/bw_fixed.c index 6ca288fb5fb9..2d46bc527b21 100644 --- a/drivers/gpu/drm/amd/display/dc/calcs/bw_fixed.c +++ b/drivers/gpu/drm/amd/display/dc/calcs/bw_fixed.c @@ -26,12 +26,12 @@ #include "bw_fixed.h" -#define MIN_I64 \ - (int64_t)(-(1LL << 63)) - #define MAX_I64 \ (int64_t)((1ULL << 63) - 1) +#define MIN_I64 \ + (-MAX_I64 - 1) + #define FRACTIONAL_PART_MASK \ ((1ULL << BW_FIXED_BITS_PER_FRACTIONAL_PART) - 1)