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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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