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Date: Thu, 8 Oct 2020 23:49:27 -0700 From: Yonghong Song <yhs@...com> To: Alexei Starovoitov <alexei.starovoitov@...il.com>, <davem@...emloft.net> CC: <daniel@...earbox.net>, <john.fastabend@...il.com>, <netdev@...r.kernel.org>, <bpf@...r.kernel.org>, <kernel-team@...com> Subject: Re: [PATCH v2 bpf-next 3/4] selftests/bpf: Add profiler test On 10/8/20 6:12 PM, Alexei Starovoitov wrote: > From: Alexei Starovoitov <ast@...nel.org> > > The main purpose of the profiler test to check different llvm generation > patterns to make sure the verifier can load these large programs. > > Note that profiler.inc.h test doesn't follow strict kernel coding style. > The code was formatted in the kernel style, but variable declarations are > kept as-is to preserve original llvm IR pattern. > > profiler1.c should pass with older and newer llvm > > profiler[23].c may fail on older llvm that don't have: > https://reviews.llvm.org/D85570 Not sure but the below equivalent URL may be more intuitive: https://reviews.llvm.org/D85570 > because llvm may do speculative code motion optimization that > will generate code like this: > > // r9 is a pointer to map_value > // r7 is a scalar > 17: bf 96 00 00 00 00 00 00 r6 = r9 > 18: 0f 76 00 00 00 00 00 00 r6 += r7 > 19: a5 07 01 00 01 01 00 00 if r7 < 257 goto +1 > 20: bf 96 00 00 00 00 00 00 r6 = r9 > // r6 is used here > > The verifier will reject such code with the error: > "math between map_value pointer and register with unbounded min value is not allowed" > At insn 18 the r7 is indeed unbounded. The later insn 19 checks the bounds and > the insn 20 undoes map_value addition. It is currently impossible for the > verifier to understand such speculative pointer arithmetic. Hence llvm D85570 > addresses it on the compiler side. > > Signed-off-by: Alexei Starovoitov <ast@...nel.org> Acked-by: Yonghong Song <yhs@...com>
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