Messages in this thread | | | Subject | Re: [PATCH 3/3] Fix insn.c misaligned address error | From | Adrian Hunter <> | Date | Tue, 30 Jul 2019 10:53:19 +0300 |
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On 30/07/19 3:47 AM, Masami Hiramatsu wrote: > On Mon, 29 Jul 2019 11:22:34 +0300 > Adrian Hunter <adrian.hunter@intel.com> wrote: > >> On 27/07/19 12:46 PM, Masami Hiramatsu wrote: >>> On Fri, 26 Jul 2019 16:38:06 -0300 >>> Arnaldo Carvalho de Melo <acme@kernel.org> wrote: >>> >>>> Em Wed, Jul 24, 2019 at 11:45:12AM -0700, Numfor Mbiziwo-Tiapo escreveu: >>>>> The ubsan (undefined behavior sanitizer) version of perf throws an >>>>> error on the 'x86 instruction decoder - new instructions' function >>>>> of perf test. >>>>> >>>>> To reproduce this run: >>>>> make -C tools/perf USE_CLANG=1 EXTRA_CFLAGS="-fsanitize=undefined" >>>>> >>>>> then run: tools/perf/perf test 62 -v >>>>> >>>>> The error occurs in the __get_next macro (line 34) where an int is >>>>> read from a potentially unaligned address. Using memcpy instead of >>>>> assignment from an unaligned pointer. >>>> >>>> Since this came from the kernel, don't we have to fix it there as well? >>>> Masami, Adrian? >>> >>> I guess we don't need it, since x86 can access "unaligned address" and >>> x86 insn decoder in kernel runs only on x86. I'm not sure about perf's >>> that part. Maybe if we run it on other arch as cross-arch application, >>> it may cause unaligned pointer issue. >> >> Yes, theoretically Intel PT decoding can be done on any arch. >> >> But the memcpy is probably sub-optimal for x86, so the patch as it stands >> does not seem suitable. I notice the kernel has get_unaligned() and >> put_unaligned(). >> >> Obviously it would be better for a patch to be accepted to >> arch/x86/lib/insn.c also. > > Hmm, then I rather like memcpy() for arch/x86/lib/insn.c, because it runs only > on x86.
Yes, I was wrong about memcpy, and it is simpler for perf tools than dragging out get_unaligned().
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