[LLVMbugs] [Bug 13551] New: Bus error / Segmentation Fault in generated code on generated vector copy

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http://llvm.org/bugs/show_bug.cgi?id=13551

             Bug #: 13551
           Summary: Bus error / Segmentation Fault in generated code on
                    generated vector copy
           Product: new-bugs
           Version: 3.1
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: cyclaero at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified


The following has been confirmed with clang version 3.1 (branches/release_31)
Target: i386-portbld-freebsd8.3 (32bit) and on Mac OS X 10.7.4 clang version
4.0 (tags/Apple/clang-421.0.57) (based on LLVM 3.1svn) Target:
x86_64-apple-darwin11.4.0 (64bit).

Please consider the following C example employing 128bit vector operation for
string copying:

BEGIN OF EXAMPLE
----------------

#include <stdio.h>
#include <stdint.h>
#include <string.h>

static inline size_t strmcpy(char *dest, const char *src, size_t m)
{
   typedef uint8_t uint128v __attribute__((__vector_size__(16)));

   size_t k, l = strlen(src);
   switch (m = (l < m) ? l : m-1)
   {
      default:
         for (k = 0;    k  < m>>4; k++)
            ((uint128v *)dest)[k] = ((uint128v *)src)[k];  // <-- Bus Error
      case 8 ... 15:
         if ((k = m>>4<<1) < m>>3)
            ((uint64_t *)dest)[k] = ((uint64_t *)src)[k];
      case 4 ... 7:
         if ((k = m>>3<<1) < m>>2)
            ((uint32_t *)dest)[k] = ((uint32_t *)src)[k];
      case 2 ... 3:
         if ((k = m>>2<<1) < m>>1)
            ((uint16_t *)dest)[k] = ((uint16_t *)src)[k];
      case 1:
         if ((k = m>>1<<1) < m)
            dest[k] = src[k];
      case 0:
         ;
   }
   dest[m] = '\0';
   return m;
}

int main(int argc, const char *argv[])
{
   char   buffer[256];
   size_t m = strmcpy(buffer, "\
Strings bigger than 15 chars would be copied using 128bit vectors.\n\
The present code works fine when compiled with -O3, however, when\n\
compiled with -O0, it produces a Bus Error on FreeBSD 8.3 and a\n\
Seg. fault on Mac OS X 10.7.4 at the indicated position.", 256);

   printf("\n%s\n\n%zd bytes copied\n\n", buffer, m);
   return 0;
}

--------------
END OF EXAMPLE


Tests on FreeBSD 8.3 - 32bit:

$clang -O0 -mssse3 strmcpy.c && ./a.out
Bus error: 10 (core dumped)

$clang -O3 -mssse3 strmcpy.c && ./a.out

Strings bigger than 15 chars would be copied using 128bit vectors.
The present code works fine when compiled with -O3, however, when
compiled with -O0, it produces a Bus Error on FreeBSD 8.3 and a
Seg. fault on Mac OS X 10.7.4 at the indicated position.

253 bytes copied
----------------

Tests on Mac OS 10.7.4 (Mac OS 10.7.4):

$clang -O0 -mssse3 -arch i386 strmcpy.c && ./a.out
Segmentation fault: 11

$clang -O0 -mssse3 -arch x86_64 strmcpy.c && ./a.out
Segmentation fault: 11

$ clang -O3 -mssse3 -arch i386 strmcpy.c && ./a.out

Strings bigger than 15 chars would be copied using 128bit vectors.
The present code works fine when compiled with -O3, however, when
compiled with -O0, it produces a Bus Error on FreeBSD 8.3 and a
Seg. fault on Mac OS X 10.7.4 at the indicated position.

253 bytes copied

$ clang -O3 -mssse3 -arch x86_64 strmcpy.c && ./a.out

Strings bigger than 15 chars would be copied using 128bit vectors.
The present code works fine when compiled with -O3, however, when
compiled with -O0, it produces a Bus Error on FreeBSD 8.3 and a
Seg. fault on Mac OS X 10.7.4 at the indicated position.

253 bytes copied


Best regards

Rolf Jansen

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