mem: add memtaint().

Useful if you're going to reuse a buffer later.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/ccan/mem/mem.c b/ccan/mem/mem.c
index 5eb15070ed3c3f9f5bf8d2dd8b0d0f060ffa1766..13027a2a7b0fec1b18ae386f9704d84aed41c5f1 100644 (file)
--- a/ccan/mem/mem.c
+++ b/ccan/mem/mem.c
@@ -107,3 +107,22 @@ bool memeqzero(const void *data, size_t length)
        /* Now we know that's zero, memcmp with self. */
        return memcmp(data, p, length) == 0;
 }
        /* Now we know that's zero, memcmp with self. */
        return memcmp(data, p, length) == 0;
 }

+
+void memtaint(void *data, size_t len)
+{
+       /* Using 16 bytes is a bit quicker than 4 */
+       const unsigned tainter[]
+               = { 0xdeadbeef, 0xdeadbeef, 0xdeadbeef, 0xdeadbeef };
+       char *p = data;
+
+       while (len >= sizeof(tainter)) {
+               memcpy(p, tainter, sizeof(tainter));
+               p += sizeof(tainter);
+               len -= sizeof(tainter);
+       }
+       memcpy(p, tainter, len);
+
+#if HAVE_VALGRIND_MEMCHECK_H
+       VALGRIND_MAKE_MEM_UNDEFINED(data, len);
+#endif
+}

diff --git a/ccan/mem/mem.h b/ccan/mem/mem.h
index a3403c4ee31dc8794f89acfd95836e5c17c4672a..f2c3d5c7a6f795e2e091df8a545992c6533b50ec 100644 (file)
--- a/ccan/mem/mem.h
+++ b/ccan/mem/mem.h
@@ -275,4 +275,20 @@ static inline void *memcheck_(const void *data, size_t len)
 #else
 #define memcheck(data, len) memcheck_((data), (len))
 #endif
 #else
 #define memcheck(data, len) memcheck_((data), (len))
 #endif

+
+/**
+ * memtaint - mark a memory region unused
+ * @data: start of region
+ * @len: length in bytes
+ *
+ * This writes an "0xdeadbeef" eyecatcher repeatedly to the memory.
+ * When running under valgrind, it also tells valgrind that the memory is
+ * uninitialized, triggering valgrind errors if it is used for branches
+ * or written out (or passed to memcheck!) in future.
+ *
+ * Example:
+ *     // We'll reuse this buffer later, but be sure we don't access it.
+ *     memtaint(somebytes, bytes_len);
+ */
+void memtaint(void *data, size_t len);

 #endif /* CCAN_MEM_H */
 #endif /* CCAN_MEM_H */