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    SubjectRe: [PATCH 3/3] Fix insn.c misaligned address error
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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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