Hi,
your analysis is perfect. The SSE2 code of PCRE-JIT perform aligned wide loads, and ignores the loaded data before and after the input buffer.
I don't really know much about suppressing valgrind errors.
Regards,
Zoltan
Tavian Barnes <tavianator@???> írta:
>The following test case produces Valgrind errors on x86-64 with 10.21,
>whereas it did not with 10.20. I suspect it has to do with the
>introduction of SSE support.
>
>$ cat foo.c
>#define PCRE2_CODE_UNIT_WIDTH 8
>#include <pcre2.h>
>#include <stdlib.h>
>#include <string.h>
>
>int main()
>{
> char regex[4], subject[4];
> strcpy(regex, "a");
> strcpy(subject, "b");
> /* regex[3..4] and subject[3..4] are uninitialized */
>
> int errorcode;
> PCRE2_SIZE erroroffset;
> pcre2_code *code = pcre2_compile(
> (PCRE2_SPTR)regex,
> PCRE2_ZERO_TERMINATED,
> PCRE2_UCP | PCRE2_UTF,
> &errorcode,
> &erroroffset,
> NULL
> );
> pcre2_jit_compile(code, PCRE2_JIT_COMPLETE);
>
> pcre2_match_data *match_data =
>pcre2_match_data_create_from_pattern(code, NULL);
> int err = pcre2_match(
> code,
> (PCRE2_SPTR)subject,
> PCRE2_ZERO_TERMINATED,
> 0,
> 0,
> match_data,
> NULL
> );
>
> return err = PCRE2_ERROR_NOMATCH ? EXIT_SUCCESS : EXIT_FAILURE;
>}
>$ gcc foo.c -lpcre2-8 -o foo
>$ valgrind -q ./foo
>==18980== Conditional jump or move depends on uninitialised value(s)
>==18980== at 0x40230C8: ???
>==18980== by 0xFFEFFFD9F: ???
>==18980== by 0xFFEFF7A4F: ???
>
>I suspect that it's not really a bug in the generated code; it's
>probably just doing a wide load on the subject string and masking away
>(or otherwise ignoring) the characters past the end. It looks like
>the load is always aligned so there's no worries about hitting an
>unreadable page that's right after the subject string.
>
>If you use valgrind --gen-suppressions=yes, the generated suppression
>will be too aggressive, suppressing uninitialized value errors
>*everywhere*. To suppress just those from the JIT code, use:
>
>$ cat valgrind.supp
>{
> PCRE2 JIT wide loads
> Memcheck:Cond
> obj:???
>}
>
>--
>Tavian Barnes
>
>--
>## List details at https://lists.exim.org/mailman/listinfo/pcre-dev
