X-Git-Url: https://git.tcpdump.org/tcpdump/blobdiff_plain/c672f002763b3a4fc30ca229e57f50d3b2e6d766..fb8b947488c7f22b518de1df1a91e663dc7ab33c:/extract.h?ds=sidebyside

diff --git a/extract.h b/extract.h
index 0117f389..df5684f4 100644
--- a/extract.h
+++ b/extract.h
@@ -18,40 +18,81 @@
  * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
  *
- * @(#) $Header: /tcpdump/master/tcpdump/extract.h,v 1.17 2001-09-17 21:57:52 fenner Exp $ (LBL)
+ * @(#) $Header: /tcpdump/master/tcpdump/extract.h,v 1.19 2002-12-11 07:13:51 guy Exp $ (LBL)
  */
 
 /* Network to host order macros */
 
 #ifdef LBL_ALIGN
+/*
+ * The processor doesn't natively handle unaligned loads.
+ */
+#ifdef HAVE___ATTRIBUTE__
+/*
+ * We have __attribute__; we assume that means we have __attribute__((packed)).
+ * Declare packed structures containing a u_int16_t and a u_int32_t,
+ * cast the pointer to point to one of those, and fetch through it;
+ * the GCC manual doesn't appear to explicitly say that
+ * __attribute__((packed)) causes the compiler to generate unaligned-safe
+ * code, but it apppears to do so.
+ *
+ * We do this in case the compiler can generate, for this instruction set,
+ * better code to do an unaligned load and pass stuff to "ntohs()" or
+ * "ntohl()" than the code to fetch the bytes one at a time and
+ * assemble them.  (That might not be the case on a little-endian platform,
+ * where "ntohs()" and "ntohl()" might not be done inline.)
+ */
+typedef struct {
+	u_int16_t	val;
+} __attribute__((packed)) unaligned_u_int16_t;
+
+typedef struct {
+	u_int32_t	val;
+} __attribute__((packed)) unaligned_u_int32_t;
+
 #define EXTRACT_16BITS(p) \
-	((u_int16_t)*((const u_int8_t *)(p) + 0) << 8 | \
-	(u_int16_t)*((const u_int8_t *)(p) + 1))
+	((u_int16_t)ntohs(((const unaligned_u_int16_t *)(p))->val))
 #define EXTRACT_32BITS(p) \
-	((u_int32_t)*((const u_int8_t *)(p) + 0) << 24 | \
-	(u_int32_t)*((const u_int8_t *)(p) + 1) << 16 | \
-	(u_int32_t)*((const u_int8_t *)(p) + 2) << 8 | \
-	(u_int32_t)*((const u_int8_t *)(p) + 3))
-#else
+	((u_int32_t)ntohl(((const unaligned_u_int32_t *)(p))->val))
+#else /* HAVE___ATTRIBUTE__ */
+/*
+ * We don't have __attribute__, so do unaligned loads of big-endian
+ * quantities the hard way - fetch the bytes one at a time and
+ * assemble them.
+ */
+#define EXTRACT_16BITS(p) \
+	((u_int16_t)((u_int16_t)*((const u_int8_t *)(p) + 0) << 8 | \
+		     (u_int16_t)*((const u_int8_t *)(p) + 1)))
+#define EXTRACT_32BITS(p) \
+	((u_int32_t)((u_int32_t)*((const u_int8_t *)(p) + 0) << 24 | \
+		     (u_int32_t)*((const u_int8_t *)(p) + 1) << 16 | \
+		     (u_int32_t)*((const u_int8_t *)(p) + 2) << 8 | \
+		     (u_int32_t)*((const u_int8_t *)(p) + 3)))
+#endif /* HAVE___ATTRIBUTE__ */
+#else /* LBL_ALIGN */
+/*
+ * The processor natively handles unaligned loads, so we can just
+ * cast the pointer and fetch through it.
+ */
 #define EXTRACT_16BITS(p) \
 	((u_int16_t)ntohs(*(const u_int16_t *)(p)))
 #define EXTRACT_32BITS(p) \
 	((u_int32_t)ntohl(*(const u_int32_t *)(p)))
-#endif
+#endif /* LBL_ALIGN */
 
 #define EXTRACT_24BITS(p) \
-	((u_int32_t)*((const u_int8_t *)(p) + 0) << 16 | \
-	(u_int32_t)*((const u_int8_t *)(p) + 1) << 8 | \
-	(u_int32_t)*((const u_int8_t *)(p) + 2))
+	((u_int32_t)((u_int32_t)*((const u_int8_t *)(p) + 0) << 16 | \
+		     (u_int32_t)*((const u_int8_t *)(p) + 1) << 8 | \
+		     (u_int32_t)*((const u_int8_t *)(p) + 2)))
 
 /* Little endian protocol host order macros */
 
 #define EXTRACT_LE_8BITS(p) (*(p))
 #define EXTRACT_LE_16BITS(p) \
-	((u_int16_t)*((const u_int8_t *)(p) + 1) << 8 | \
-	(u_int16_t)*((const u_int8_t *)(p) + 0))
+	((u_int16_t)((u_int16_t)*((const u_int8_t *)(p) + 1) << 8 | \
+		     (u_int16_t)*((const u_int8_t *)(p) + 0)))
 #define EXTRACT_LE_32BITS(p) \
-	((u_int32_t)*((const u_int8_t *)(p) + 3) << 24 | \
-	(u_int32_t)*((const u_int8_t *)(p) + 2) << 16 | \
-	(u_int32_t)*((const u_int8_t *)(p) + 1) << 8 | \
-	(u_int32_t)*((const u_int8_t *)(p) + 0))
+	((u_int32_t)((u_int32_t)*((const u_int8_t *)(p) + 3) << 24 | \
+		     (u_int32_t)*((const u_int8_t *)(p) + 2) << 16 | \
+		     (u_int32_t)*((const u_int8_t *)(p) + 1) << 8 | \
+		     (u_int32_t)*((const u_int8_t *)(p) + 0)))