Add memcpy_safe

ISO/IEC 9899:1999 §7.21.1/2 says:
Where an argument declared as size_t n specifies the length of the array
for a function, n can have the value zero on a call to that
function. Unless explicitly stated otherwise in the description of a
particular function in this subclause, pointer arguments on such a call
shall still have valid values, as described in 7.1.4.

In base64_append_width memcpy was called as memcpy(x, NULL, 0).  GCC 4.9
started making use of this and assumes This worked fine under -O0, but
does something strange under -O3.

This patch fixes a bug in base64_append_width(), fixes a possible bug in
journal_file_append_entry_internal(), and makes use of the new function
to simplify the code in other places.

1 files changed, 1 insertions, 2 deletions

diff --git a/src/resolve/resolved-dns-packet.c b/src/resolve/resolved-dns-packet.c
index 5cbe20832f..abb9725b73 100644
--- a/src/resolve/resolved-dns-packet.c
+++ b/src/resolve/resolved-dns-packet.c
@@ -433,8 +433,7 @@ int dns_packet_append_raw_string(DnsPacket *p, const void *s, size_t size, size_
 
         ((uint8_t*) d)[0] = (uint8_t) size;
 
-        if (size > 0)
-                memcpy(((uint8_t*) d) + 1, s, size);
+        memcpy_safe(((uint8_t*) d) + 1, s, size);
 
         return 0;
 }