Utilize the stronger guarantees on the call arguments from the

harvester, which now always calls hwrngs with the buffer length
multiple of the word size.  This allows to remove the excessive memory
accesses to temporary buffer when saving the entropy word.

Streamline the assembly and unify it between i386 and amd64.

Reviewed by:	markm, des
Approved by:	so (des)
Sponsored by:	The FreeBSD Foundation
MFC after:	2 weeks

1 files changed, 25 insertions, 32 deletions

diff --git a/sys/dev/random/ivy.c b/sys/dev/random/ivy.c
index 7784e8b..9b40016 100644
--- a/sys/dev/random/ivy.c
+++ b/sys/dev/random/ivy.c
@@ -1,8 +1,12 @@
 /*-
+ * Copyright (c) 2013 The FreeBSD Foundation
  * Copyright (c) 2013 David E. O'Brien <obrien@NUXI.org>
  * Copyright (c) 2012 Konstantin Belousov <kib@FreeBSD.org>
  * All rights reserved.
  *
+ * Portions of this software were developed by Konstantin Belousov
+ * under sponsorship from the FreeBSD Foundation.
+ *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
@@ -58,26 +62,25 @@ static struct random_hardware_source random_ivy = {
 };
 
 static inline int
-ivy_rng_store(uint64_t *tmp)
+ivy_rng_store(long *buf)
 {
 #ifdef __GNUCLIKE_ASM
-	uint32_t count;
+	long tmp;
+	int retry;
 
+	retry = RETRY_COUNT;
 	__asm __volatile(
-#ifdef __amd64__
-	    "rdrand\t%%rax\n\t"
-	    "jnc\t1f\n\t"
-	    "movq\t%%rax,%1\n\t"
-	    "movl\t$8,%%eax\n"
-#else /* i386 */
-	    "rdrand\t%%eax\n\t"
-	    "jnc\t1f\n\t"
-	    "movl\t%%eax,%1\n\t"
-	    "movl\t$4,%%eax\n"
-#endif
-	    "1:\n"	/* %eax is cleared by processor on failure */
-	    : "=a" (count), "=g" (*tmp) : "a" (0) : "cc");
-	return (count);
+	    "1:\n\t"
+	    "rdrand	%2\n\t"	/* read randomness into tmp */
+	    "jb		2f\n\t" /* CF is set on success, exit retry loop */
+	    "dec	%0\n\t" /* otherwise, retry-- */
+	    "jne	1b\n\t" /* and loop if retries are not exhausted */
+	    "jmp	3f\n"	/* failure, retry is 0, used as return value */
+	    "2:\n\t"
+	    "mov	%2,%1\n\t" /* *buf = tmp */
+	    "3:"
+	    : "+q" (retry), "=m" (*buf), "=q" (tmp) : : "cc");
+	return (retry);
 #else /* __GNUCLIKE_ASM */
 	return (0);
 #endif
@@ -86,23 +89,13 @@ ivy_rng_store(uint64_t *tmp)
 static int
 random_ivy_read(void *buf, int c)
 {
-	uint8_t *b;
-	int count, ret, retry;
-	uint64_t tmp;
-
-	b = buf;
-	for (count = c; count > 0; count -= ret) {
-		for (retry = 0; retry < RETRY_COUNT; retry++) {
-			ret = ivy_rng_store(&tmp);
-			if (ret != 0)
-				break;
-		}
-		if (ret == 0)
+	long *b;
+	int count;
+
+	KASSERT(c % sizeof(long) == 0, ("partial read %d", c));
+	for (b = buf, count = c; count > 0; count -= sizeof(long), b++) {
+		if (ivy_rng_store(b) == 0)
 			break;
-		if (ret > count)
-			ret = count;
-		memcpy(b, &tmp, ret);
-		b += ret;
 	}
 	return (c - count);
 }