tweak buffer handling a bit:

- make BufExpand a real function, zap BufOverflow
- sprinkle assert that justify the arithmetic
- use unsigned constants
- fix a bug in the unlikely condition where Buf_printf would exactly
match the buffer boundary and Buf_Retrieve would be called right after

okay millert@

2 files changed, 29 insertions, 36 deletions

diff --git a/usr.bin/make/buf.c b/usr.bin/make/buf.c
index 868653ac887..f5e3f8bd9b9 100644
--- a/usr.bin/make/buf.c
+++ b/usr.bin/make/buf.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: buf.c,v 1.27 2015/04/29 00:42:12 millert Exp $	*/
+/*	$OpenBSD: buf.c,v 1.28 2019/12/21 15:26:47 espie Exp $	*/
 /*	$NetBSD: buf.c,v 1.9 1996/12/31 17:53:21 christos Exp $ */
 
 /*
@@ -66,6 +66,7 @@
  *	Functions for automatically expanded buffers.
  */
 
+#include <assert.h>
 #include <ctype.h>
 #include <limits.h>
 #include <stddef.h>
@@ -96,45 +97,37 @@ fatal_overflow()
 	exit(2);
 }
 
-/* BufExpand(bp, nb)
- *	Expand buffer bp to hold upto nb additional
- *	chars.	Makes sure there's room for an extra '\0' char at
- *	the end of the buffer to terminate the string.	*/
-#define BufExpand(bp,nb)				\
-do {							\
-	size_t   occupied = (bp)->inPtr - (bp)->buffer;	\
-	size_t   size = (bp)->endPtr - (bp)->buffer;	\
-	DO_STAT_BUF(bp, nb);				\
-							\
-	do {						\
-		if (size <= SIZE_MAX/2) {		\
-			size *= 2 ;			\
-		} else {				\
-			fatal_overflow();		\
-		}					\
-	} while (size - occupied < (nb)+1+BUF_MARGIN);	\
-	(bp)->buffer = (bp)->inPtr = (bp)->endPtr = 	\
-		erealloc((bp)->buffer, size);		\
-	(bp)->inPtr += occupied;			\
-	(bp)->endPtr += size;				\
-} while (0);
-
-#define BUF_DEF_SIZE	256	/* Default buffer size */
-#define BUF_MARGIN	256	/* Make sure we are comfortable */
+#define BUF_DEF_SIZE	256U	/* Default buffer size */
+#define BUF_MARGIN	256U	/* Make sure we are comfortable */
 
-/* the hard case for Buf_AddChar: buffer must be expanded to accommodate
- * one more char.  */
+/* BufExpand(bp, nb)
+ *	Expand buffer bp to hold up to nb additional
+ *	chars.	Makes sure there's always room for an extra '\0' char 
+ *	at the end of the buffer for Buf_Retrieve. */
 void
-BufOverflow(Buffer bp)
+BufExpand(Buffer bp, size_t nb)
 {
-	BufExpand(bp, 1);
-}
+	size_t   occupied = bp->inPtr - bp->buffer;
+	size_t   size = bp->endPtr - bp->buffer;
+	DO_STAT_BUF(bp, nb);
 
+	do {
+		if (size <= SIZE_MAX/2) {
+			size *= 2 ;
+		} else {
+			fatal_overflow();
+		}
+		assert(size >= occupied);
+	} while (size - occupied < nb+1+BUF_MARGIN);
+	bp->buffer = erealloc(bp->buffer, size);
+	bp->inPtr = bp->buffer +occupied;
+	bp->endPtr = bp->buffer + size;
+}
 
 void
 Buf_AddChars(Buffer bp, size_t numBytes, const char *bytesPtr)
 {
-
+	assert(bp->endPtr >= bp->inPtr);
 	if ((size_t)(bp->endPtr - bp->inPtr) < numBytes+1)
 		BufExpand(bp, numBytes);
 
@@ -150,7 +143,7 @@ Buf_printf(Buffer bp, const char *fmt, ...)
 	va_start(va, fmt);
 	n = vsnprintf(bp->inPtr, bp->endPtr - bp->inPtr, fmt, va);
 	va_end(va);
-	if (n > bp->endPtr - bp->inPtr) {
+	if (n+1 > bp->endPtr - bp->inPtr) {
 		va_list vb;
 		BufExpand(bp, n);
 		va_start(vb, fmt);
diff --git a/usr.bin/make/buf.h b/usr.bin/make/buf.h
index 018002c2397..6a31142b289 100644
--- a/usr.bin/make/buf.h
+++ b/usr.bin/make/buf.h
@@ -1,7 +1,7 @@
 #ifndef _BUF_H
 #define _BUF_H
 
-/*	$OpenBSD: buf.h,v 1.22 2012/11/07 14:18:41 espie Exp $	*/
+/*	$OpenBSD: buf.h,v 1.23 2019/12/21 15:26:47 espie Exp $	*/
 /*	$NetBSD: buf.h,v 1.7 1996/12/31 17:53:22 christos Exp $ */
 
 /*
@@ -85,7 +85,7 @@ typedef struct Buffer_ {
 } BUFFER;
 
 /* Internal support for Buf_AddChar.  */
-extern void BufOverflow(Buffer);
+extern void BufExpand(Buffer, size_t);
 
 
 /* User interface */
@@ -117,7 +117,7 @@ extern void Buf_Init(Buffer, size_t);
 #define Buf_AddChar(bp, byte)			\
 do {						\
 	if ((bp)->endPtr - (bp)->inPtr <= 1)	\
-	    BufOverflow(bp);			\
+	    BufExpand(bp, 1);			\
 	*(bp)->inPtr++ = (byte);		\
 } while (0)