[uclibc-ng-devel] memmove() is failing on MIPS CPU

Rene Nielsen rene.nielsen at microsemi.com
Thu Apr 21 15:30:29 CEST 2016

I have found a bug in .../libc/string/generic/memmove.c, which is the one that
MIPS uses, since there's no specialized, optimized version for MIPS.

We're currently using uClibc v. 1.0.12, but I suspect the bug to be present in
earlier releases too.

Here's a snippet from memmove.c#memmove():
  /* This test makes the forward copying code be used whenever possible.
     Reduces the working set.  */
  if (dstp - srcp >= len)       /* *Unsigned* compare!  */
      /* Backward memcpy implementation cannot be used */
      memcpy(dest, src, len);
      /* Copy from the beginning to the end.  */

Given the name of the define (__ARCH_HAS_BWD_MEMCPY__) it sounds as when this is
defined, the architecture indeed has backward memcpy() support. But how come the
line is preceded by #ifndef and not #ifdef, when the code inside calls memcpy()?

Also, the first comment inside the #ifndef seems odd, since memcpy() indeed is called:
  /* Backward memcpy implementation cannot be used */

Our SDK does not define __ARCH_HAS_BWD_MEMCPY__, so when memmove()
resorts to a simple memcpy() that does the wrong thing for overlapping regions,
our application fails with disastrous side-effects.

I have attached a patch that fixes this.

Please CC me in case of any inquiries/replies: rene.nielsen (at) microsemi.com

Thanks & regards,
Rene Schipp von Branitz Nielsen

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