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tile: allow memcpy(p, p, n) without corrupting memory at "p"

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Although this is not required by the definition of memcpy(),
in practice this sort of thing does happen, and it's easy to make
the code robust by doing nothing in this case.  (Since structure
copy causes the compiler to emit a memcpy, in the case where the
target structure is the same as the destination, we were seeing
corruption.)
This commit is contained in:
Chris Metcalf 2012-05-11 17:59:23 -04:00
parent cbf92fc466
commit 575298fcd2
2 changed files with 17 additions and 1 deletions
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5
ChangeLog.tile
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@ -1,3 +1,8 @@
2012-05-12 Chris Metcalf <cmetcalf@tilera.com>
* sysdeps/tile/tilegx/memcpy.c: Allow memcpy(p, p, n)
without corrupting memory at "p".
2012-05-12 Chris Metcalf <cmetcalf@tilera.com>
* sysdeps/tile/__tls_get_addr.S: Use __WORDSIZE, not _LP64.

13
sysdeps/tile/tilegx/memcpy.c
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@ -1,4 +1,4 @@
/* Copyright (C) 2011 Free Software Foundation, Inc.
/* Copyright (C) 2011-2012 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Chris Metcalf <cmetcalf@tilera.com>, 2011.
@ -107,6 +107,17 @@ __memcpy (void *__restrict dstv, const void *__restrict srcv, size_t n)
n -= sizeof (word_t))
*dst8++ = *src8++;
/* If copying to self, return. The test is cheap enough
that we do it despite the fact that the memcpy() contract
doesn't require us to support overlapping dst and src.
This is the most common case of overlap, and any close
overlap will cause corruption due to the wh64 below.
This case is particularly important since the compiler
will emit memcpy() calls for aggregate copies even if it
can't prove that src != dst. */
if (__builtin_expect (dst8 == src8, 0))
return dstv;
for (; n >= CHIP_L2_LINE_SIZE ();)
{
__insn_wh64 (dst8);