Fix length stored by strjoin() and optimise the implementation

The length that was stored for strjoin() was the sum of the lengths of the two argument strings. That means that if the sum was larger than STRSIZE, we would still store that larger length even though the string itself got truncated. Signed-off-by: Kris Van Hees <kris.van.hees@oracle.com> Reviewed-by: Eugene Loh <eugene.loh@oracle.com>
oracle · Nov 20, 2021 · ace8cbf · ace8cbf
1 parent cf1e9df
commit ace8cbf
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Showing 3 changed files with 94 additions and 27 deletions.
diff --git a/bpf/strjoin.S b/bpf/strjoin.S
@@ -19,39 +19,46 @@ dt_strjoin:
 	mov	%r7, %r2		/* %r7 = s1 */
 	mov	%r8, %r3		/* %r8 = s2 */
 
-	mov	%r1, %r7
-	call	dt_strlen
-	mov	%r6, %r0		/* len = dt_strlen(s1) */
-	add	%r7, DT_STRLEN_BYTES	/* s1 += 2 */
-
-	mov	%r1, %r8
-	call	dt_strlen
-	add	%r6, %r0		/* len += dt_strlen(s2) */
-	add	%r8, DT_STRLEN_BYTES	/* s2 += 2 */
-
-	mov	%r1, %r6
-	mov	%r2, %r9
-	call	dt_strlen_store		/* dt_strlen_store(len, dst) */
-	add	%r9, DT_STRLEN_BYTES	/* dst += 2 */
-
 	lddw	%r6, STRSZ
-	add	%r6, 1
-	and	%r6, 0xffffffff		/* len = (STRSZ + 1) & 0xffffffff */
+	add	%r6, 1			/* cnt = STRSZ + 1 */
 
-	mov	%r1, %r9
+	add	%r1, DT_STRLEN_BYTES	/* dst is in %r1 already */
 	mov	%r2, %r6
 	mov	%r3, %r7
-	call	BPF_FUNC_probe_read_str	/* cnt = bpf_probe_read_str(dst, len s1) */
-	jslt	%r0, 0, .L1		/* if (cnt < 0) goto .L1 */
-	jslt	%r0, 1, .L2		/* if (cnt < 1) goto .L2 */
-	sub	%r0, 1			/* cnt-- */
-	add	%r9, %r0		/* dst += cnt */
-	sub	%r6, %r0		/* len -= cnt */
-.L2:
+	add	%r3, DT_STRLEN_BYTES
+	call	BPF_FUNC_probe_read_str	/*
+					 * rc = probe_read_str(
+					 *	  &dst[DT_STRLEN_BYTES],
+					 *	  cnt,
+					 *	  &s1[DT_STRLEN_BYTES]);
+					 */
+	jsle	%r0, 0, .Lexit		/* if (rc s<= 0) goto .Lexit; */
+	mov	%r7, %r0		/* len = rc */
+	jeq	%r7, %r6, .Lset_len	/* if (len == cnt) goto .Lset_len; */
+	sub	%r7, 1			/* len-- */
+
 	mov	%r1, %r9
+	add	%r1, DT_STRLEN_BYTES
+	add	%r1, %r7
 	mov	%r2, %r6
+	sub	%r2, %r7
 	mov	%r3, %r8
-	call	BPF_FUNC_probe_read_str	/* bpf_probe_read_str(dst, len, s2 */
-.L1:
+	add	%r3, DT_STRLEN_BYTES
+	call	BPF_FUNC_probe_read_str	/*
+					 * rc = probe_read_str(
+					 *	  &dst[DT_STRLEN_BYTES + len],
+					 *	  cnt - len,
+					 *	  &s2[DT_STRLEN_BYTES]);
+					 */
+	jsle	%r0, 0, .Lexit		/* if (rc s<= 0) goto .Lset_len; */
+	add	%r7, %r0		/* len += rc */
+
+.Lset_len:
+	sub	%r7, 1			/* len-- */
+	mov	%r1, %r7
+	mov	%r2, %r9
+	call	dt_strlen_store		/* dt_strlen_store(len - 1, dst) */
+
+.Lexit:
 	exit
 	.size	dt_strjoin, .-dt_strjoin
diff --git a/test/unittest/funcs/strjoin/tst.strjoin-bordercases.d b/test/unittest/funcs/strjoin/tst.strjoin-bordercases.d
@@ -0,0 +1,32 @@
+/*
+ * Oracle Linux DTrace.
+ * Copyright (c) 2021, Oracle and/or its affiliates. All rights reserved.
+ * Licensed under the Universal Permissive License v 1.0 as shown at
+ * http://oss.oracle.com/licenses/upl.
+ */
+
+#pragma D option rawbytes
+#pragma D option strsize=5
+#pragma D option quiet
+
+BEGIN
+{
+	trace(strjoin("", "123"));
+	trace(strjoin("", "12345"));
+	trace(strjoin("", "1234567890"));
+
+	trace(strjoin("123", "abcdefgh"));
+	trace(strjoin("12345", "abcdefgh"));
+	trace(strjoin("1234567890", "abcdefgh"));
+
+	trace(strjoin("123", ""));
+	trace(strjoin("12345", ""));
+	trace(strjoin("1234567890", ""));
+
+	exit(0);
+}
+
+ERROR
+{
+	exit(1);
+}
diff --git a/test/unittest/funcs/strjoin/tst.strjoin-bordercases.r b/test/unittest/funcs/strjoin/tst.strjoin-bordercases.r
@@ -0,0 +1,28 @@
+
+             0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f  0123456789abcdef
+         0: 00 03 31 32 33 00 00 00                          ..123...
+
+             0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f  0123456789abcdef
+         0: 00 05 31 32 33 34 35 00                          ..12345.
+
+             0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f  0123456789abcdef
+         0: 00 05 31 32 33 34 35 00                          ..12345.
+
+             0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f  0123456789abcdef
+         0: 00 05 31 32 33 61 62 00                          ..123ab.
+
+             0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f  0123456789abcdef
+         0: 00 05 31 32 33 34 35 00                          ..12345.
+
+             0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f  0123456789abcdef
+         0: 00 05 31 32 33 34 35 00                          ..12345.
+
+             0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f  0123456789abcdef
+         0: 00 03 31 32 33 00 00 00                          ..123...
+
+             0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f  0123456789abcdef
+         0: 00 05 31 32 33 34 35 00                          ..12345.
+
+             0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f  0123456789abcdef
+         0: 00 05 31 32 33 34 35 00                          ..12345.
+