Messages in this thread | | | Subject | Re: [PATCH 3/3] Fix insn.c misaligned address error | From | Adrian Hunter <> | Date | Mon, 29 Jul 2019 11:22:34 +0300 |
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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.
> > Thank you, > >> >> [acme@quaco perf]$ find . -name insn.c >> ./arch/x86/lib/insn.c >> ./arch/arm/kernel/insn.c >> ./arch/arm64/kernel/insn.c >> ./tools/objtool/arch/x86/lib/insn.c >> ./tools/perf/util/intel-pt-decoder/insn.c >> [acme@quaco perf]$ diff -u ./tools/perf/util/intel-pt-decoder/insn.c ./arch/x86/lib/insn.c >> --- ./tools/perf/util/intel-pt-decoder/insn.c 2019-07-06 16:59:05.734265998 -0300 >> +++ ./arch/x86/lib/insn.c 2019-07-06 16:59:01.369202998 -0300 >> @@ -10,8 +10,8 @@ >> #else >> #include <string.h> >> #endif >> -#include "inat.h" >> -#include "insn.h" >> +#include <asm/inat.h> >> +#include <asm/insn.h> >> >> /* Verify next sizeof(t) bytes can be on the same instruction */ >> #define validate_next(t, insn, n) \ >> [acme@quaco perf]$ >> >> >> - Arnaldo >> >>> Signed-off-by: Numfor Mbiziwo-Tiapo <nums@google.com> >>> --- >>> tools/perf/util/intel-pt-decoder/insn.c | 3 ++- >>> 1 file changed, 2 insertions(+), 1 deletion(-) >>> >>> diff --git a/tools/perf/util/intel-pt-decoder/insn.c b/tools/perf/util/intel-pt-decoder/insn.c >>> index ca983e2bea8b..de1944c60aa9 100644 >>> --- a/tools/perf/util/intel-pt-decoder/insn.c >>> +++ b/tools/perf/util/intel-pt-decoder/insn.c >>> @@ -31,7 +31,8 @@ >>> ((insn)->next_byte + sizeof(t) + n <= (insn)->end_kaddr) >>> >>> #define __get_next(t, insn) \ >>> - ({ t r = *(t*)insn->next_byte; insn->next_byte += sizeof(t); r; }) >>> + ({ t r; memcpy(&r, insn->next_byte, sizeof(t)); \ >>> + insn->next_byte += sizeof(t); r; }) >>> >>> #define __peek_nbyte_next(t, insn, n) \ >>> ({ t r = *(t*)((insn)->next_byte + n); r; }) >>> -- >>> 2.22.0.657.g960e92d24f-goog >> >> -- >> >> - Arnaldo > >
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