[Qemu-devel] [PATCH v2 3/3] migration: Replace strncpy() by strpadcpy(pad='\0')

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

GCC 8 added a -Wstringop-truncation warning:

  The -Wstringop-truncation warning added in GCC 8.0 via r254630 for
  bug 81117 is specifically intended to highlight likely unintended
  uses of the strncpy function that truncate the terminating NUL
  character from the source string.

This new warning leads to compilation failures:

    CC      migration/global_state.o
  qemu/migration/global_state.c: In function 'global_state_store_running':
  qemu/migration/global_state.c:45:5: error: 'strncpy' specified bound 100 equals destination size [-Werror=stringop-truncation]
       strncpy((char *)global_state.runstate, state, sizeof(global_state.runstate));
       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  make: *** [qemu/rules.mak:69: migration/global_state.o] Error 1

The runstate name doesn't require the strings to be NUL-terminated,
therefore strncpy is the right function to use here.

We could add a #pragma GCC diagnostic ignored "-Wstringop-truncation"
around, disable the warning globally using -Wno-stringop-truncation,
but since QEMU provides the strpadcpy() which does the same purpose,
simply use it to avoid the annoying warning.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
 migration/global_state.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/migration/global_state.c b/migration/global_state.c
index 8e8ab5c51e..c7e7618118 100644
--- a/migration/global_state.c
+++ b/migration/global_state.c
@@ -42,8 +42,8 @@ int global_state_store(void)
 void global_state_store_running(void)
 {
     const char *state = RunState_str(RUN_STATE_RUNNING);
-    strncpy((char *)global_state.runstate,
-           state, sizeof(global_state.runstate));
+    strpadcpy((char *)global_state.runstate,
+              sizeof(global_state.runstate), state, '\0');
 }
 
 bool global_state_received(void)
-- 
2.17.2