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Date: Thu, 9 May 2019 16:02:56 -0700 From: Alexei Starovoitov <alexei.starovoitov@...il.com> To: Jiong Wang <jiong.wang@...ronome.com> Cc: Daniel Borkmann <daniel@...earbox.net>, Oleksandr Natalenko <oleksandr@...alenko.name>, bpf <bpf@...r.kernel.org>, Network Development <netdev@...r.kernel.org>, oss-drivers@...ronome.com Subject: Re: [PATCH bpf] nfp: bpf: fix static check error through tightening shift amount adjustment On Tue, May 7, 2019 at 9:42 AM Jiong Wang <jiong.wang@...ronome.com> wrote: > > NFP shift instruction has something special. If shift direction is left > then shift amount of 1 to 31 is specified as 32 minus the amount to shift. > > But no need to do this for indirect shift which has shift amount be 0. Even > after we do this subtraction, shift amount 0 will be turned into 32 which > will eventually be encoded the same as 0 because only low 5 bits are > encoded, but shift amount be 32 will fail the FIELD_PREP check done later > on shift mask (0x1f), due to 32 is out of mask range. Such error has been > observed when compiling nfp/bpf/jit.c using gcc 8.3 + O3. > > This issue has started when indirect shift support added after which the > incoming shift amount to __emit_shf could be 0, therefore it is at that > time shift amount adjustment inside __emit_shf should have been tightened. > > Fixes: 991f5b3651f6 ("nfp: bpf: support logic indirect shifts (BPF_[L|R]SH | BPF_X)") > Reported-by: Oleksandr Natalenko <oleksandr@...alenko.name> > Reported-by: Pablo Cascón <pablo.cascon@...ronome.com > Reviewed-by: Quentin Monnet <quentin.monnet@...ronome.com> > Reviewed-by: Jakub Kicinski <jakub.kicinski@...ronome.com> > Signed-off-by: Jiong Wang <jiong.wang@...ronome.com> Applied. Thanks
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