memccpy() gives inconsistent results on mmapped files

Keith Owens
2004-12-03T03:30:14Z

Glenn Fowler of ATT reported that memccpy() gives inconsistent results
on mmapped files. This was reported to SGI, but the bug is ia64
generic, I get the same errors on a vanilla ia64 box.

Glenn's test case follows, it has been tweaked to add a PREFAULT
option. Prefaulting the input file makes memccpy work. The problem
occurs on both glibc 2.2.4 and glibc 2.3.3.

# for i in 1 257 513 1025;do cc -DNUM=$i testmemccpy.c; ./a.out; done
FAILED NUM 1 offset 0 size 64 no match
FAILED NUM 257 offset 16384 size 8
OLD xxxxxxxx
NEW xxxxxxxN
FAILED NUM 513 offset 32768 size 8
OLD xxxxxxxx
NEW xxxxxxxN
FAILED NUM 1025 offset 65536 size 8
OLD xxxxxxxx
NEW xxxxxxxN

# for i in 1 257 513 1025;do cc -DNUM=$i -DPREFAULT testmemccpy.c; ./a.out; done
No errors.

/*
* the umpteenth linux ia64 memccpy indictment
*
* Glenn Fowler ATT
*
* creates/clobbers the file ./testmemccpy.dat
*
* fails with
*
* -DNUM=1
* -DNUM%7
* -DNUMQ3
* -DNUM\x1025
*
* works with -DOH and any -DNUM=n, n>0, n<memory-limit
*
* please eradicate the cute memccpy tricks
* surely the processor is fast enough to minimize their impact
*
* Also works with -DPREFAULT - prefaulting the mmapped file gives the
* correct results in memccpy. kaos@sgi.com
*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/mman.h>

#ifndef NUM
#define NUM 257
#endif

#if OH

#undef memccpy
#define memccpy memccpy_that_works

void* memccpy(void* as1, const void* as2, int c, size_t n)
{
char* s1 = (char*)as1;
const char* s2 = (char*)as2;
const char* ep = s2 + n;

while (s2 < ep)
if ((*s1++ = *s2++) = c)
return s1;
return 0;
}

#endif

static const char x[] = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxN";

int main()
{
char* b;
char* s;
char* e;
char* t;
long m;
int f;
char u[1024];

if ((f = open("testmemccpy.dat", O_CREAT|O_RDWR|O_TRUNC, 0666)) < 0)
{
fprintf(stderr, "creat error\n");
return 1;
}
for (m = 0; m < NUM; m++)
if (write(f, x, sizeof(x)-1) != sizeof(x)-1)
{
fprintf(stderr, "write error\n");
return 1;
}
if (lseek(f, (off_t)0, SEEK_SET))
{
fprintf(stderr, "seek error\n");
return 1;
}
m *= (sizeof(x)-1);
if (!(b = s = mmap((void*)0, m, PROT_READ|PROT_WRITE, MAP_PRIVATE, f, (off_t)0)))
{
fprintf(stderr, "mmap error\n");
return 1;
}
#ifdef PREFAULT
for (s = b; s < b+m; s+@96)
f = *s;
s = b;
#endif
for (e = s + m; s < e && (t = memccpy(u, s, 'N', (e-s) > sizeof(u) ? sizeof(u) : (e-s))); s += (t-u))
if ((t-u) != (sizeof(x)-1) || memcmp(u, s, t-u))
{
fprintf(stderr, "FAILED NUM %d offset %lu size %lu\n", NUM, (unsigned long)(s-b), (unsigned long)(t-u));
fprintf(stderr, "OLD %-.*s\n", t-u, s);
fprintf(stderr, "NEW %-.*s\n", t-u, u);
return 1;
}
if (s < e)
{
fprintf(stderr, "FAILED NUM %d offset %lu size %lu no match\n", NUM, (unsigned long)(s-b), (unsigned long)(e-s));
return 1;
}
return 0;
}