Messages in this thread | | | Date | Wed, 27 Mar 2019 11:14:52 -0700 | From | Jakub Kicinski <> | Subject | Re: [oss-drivers] [PATCH AUTOSEL 5.0 192/262] nfp: bpf: correct the behavior for shifts by zero |
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On Wed, 27 Mar 2019 14:00:47 -0400, Sasha Levin wrote: > From: Jiong Wang <jiong.wang@netronome.com> > > [ Upstream commit db0a4b3b6b83a081a9ec309cc8178e5c9b4706a5 ] > > Shifts by zero do nothing, and should be treated as nops. > > Even though compiler is not supposed to generate such instructions and > manual written assembly is unlikely to have them, but they are legal > instructions and have defined behavior. > > This patch correct existing shifts code-gen to make sure they do nothing > when shift amount is zero except when the instruction is ALU32 for which > high bits need to be cleared. > > For shift amount bigger than type size, already, NFP JIT back-end errors > out for immediate shift and only low 5 bits will be taken into account for > indirect shift which is the same as x86. > > Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com> > Signed-off-by: Jiong Wang <jiong.wang@netronome.com> > Signed-off-by: Alexei Starovoitov <ast@kernel.org> > Signed-off-by: Sasha Levin <sashal@kernel.org>
Nope.
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