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author | Mike Frysinger <vapier@gentoo.org> | 2007-01-29 17:52:29 +0000 |
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committer | Mike Frysinger <vapier@gentoo.org> | 2007-01-29 17:52:29 +0000 |
commit | 3e0a1f38828a309fda3e9b89bb2e9ffa5ba6387d (patch) | |
tree | 0a5b1459b5c9a5d738434662a36992407b8470c6 /libc/string/memmem.c | |
parent | c5db1d4612f80820cdf2123674c6771892ef5ea9 (diff) |
Richard Sandiford writes:
However, retesting on m68k showed up a problem that had appeared in
uClibc since the last time I tried. Specifically, revision 15785 did:
-#define HEAP_GRANULARITY (sizeof (HEAP_GRANULARITY_TYPE))
+#define HEAP_GRANULARITY (__alignof__ (HEAP_GRANULARITY_TYPE))
-#define MALLOC_ALIGNMENT (sizeof (double))
+#define MALLOC_ALIGNMENT (__alignof__ (double))
The problem is that
(a) MALLOC_HEADER_SIZE == MALLOC_ALIGNMENT
(b) the header contains a size value of type size_t
(c) sizeof (size_t) is 4 on m68k, but...
(d) __alignof__ (double) is only 2 (the largest alignment used on m68k)
So we only allocate 2 bytes for the 4-byte header, and the least
significant 2 bytes of the size are in the user's area rather than
the header. The patch below fixes that problem by redefining
MALLOC_HEADER_SIZE to:
MAX (MALLOC_ALIGNMENT, sizeof (size_t))
(but without the help of the MAX macro ;)). However, we really would
like to have word alignment on Coldfire. It makes a big performance
difference, and because we have to allocate a 4-byte header anyway,
what wastage there is will be confined to the end of the allocated block.
Any wastage will also be limited to 2 bytes per allocation compared to
the current alignment.
I've therefore used the __aligned__ type attribute to create a double
type that has at least sizeof (size_t) bytes of alignment. I've
introduced a new __attribute_aligned__ macro for this. It might seem
silly protecting against old or non-GNU compilers here, but the extra
alignment is only an optimisation, and having the macro is more in the
spirit of the other attribute code.
Diffstat (limited to 'libc/string/memmem.c')
0 files changed, 0 insertions, 0 deletions