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padding align to ptr size

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Signed-off-by: Andy Green <andy.green@linaro.org>
This commit is contained in:
Bruce Perens 2015-10-13 09:17:39 +08:00 • committed by Andy Green
parent fdd3f09dd7
commit 173e9c4ea2
1 changed files with 15 additions and 1 deletions
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16
lib/libwebsockets.h
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@ -1219,7 +1219,21 @@ libwebsocket_set_timeout(struct libwebsocket *wsi,
* the big length style
*/
#define LWS_SEND_BUFFER_PRE_PADDING (4 + 10 + (2 * MAX_MUX_RECURSION))
// Pad LWS_SEND_BUFFER_PRE_PADDING to the CPU word size, so that word references
// to the address immediately after the padding won't cause an unaligned access
// error. Sometimes the recommended padding is even larger than the size of a void *.
// For example, for the X86-64 architecture, in Intel's document
// https://software.intel.com/en-us/articles/data-alignment-when-migrating-to-64-bit-intel-architecture
// they recommend that structures larger than 16 bytes be aligned to 16-byte
// boundaries.
//
#if __x86_64__
#define _LWS_PAD_SIZE 16 // Intel recommended for best performance.
#else
#define _LWS_PAD_SIZE sizeof(void *) // The pointer size on any unknown arch.
#endif
#define _LWS_PAD(n) (((n) % _LWS_PAD_SIZE) ? (n + (_LWS_PAD_SIZE - (n % _LWS_PAD_SIZE))) : (n))
#define LWS_SEND_BUFFER_PRE_PADDING _LWS_PAD(4 + 10 + (2 * MAX_MUX_RECURSION))
#define LWS_SEND_BUFFER_POST_PADDING 4
LWS_VISIBLE LWS_EXTERN int