qtest: Avoid passing raw strings through hmp()

hmp() passes its string argument through the sprintf() family;
with a proper attribute, gcc -Wformat warns us when we do something
dangerous like passing a non-constant format string.  Fortunately,
all our strings were safe, but checking whether the string can
contain an unintended % is easy to avoid and therefore worth doing.
Signed-off-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NDr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: NThomas Huth <thuth@redhat.com>
Signed-off-by: NThomas Huth <thuth@redhat.com>

tests/libqtest.h

@@ -134,14 +134,14 @@ QDict *qtest_qmp_eventwait_ref(QTestState *s, const char *event);
 /**
  * qtest_hmp:
  * @s: #QTestState instance to operate on.
- * @fmt...: HMP command to send to QEMU
+ * @fmt...: HMP command to send to QEMU, formats arguments like sprintf().
  *
  * Send HMP command to QEMU via QMP's human-monitor-command.
  * QMP events are discarded.
  *
  * Returns: the command's output.  The caller should g_free() it.
  */
-char *qtest_hmp(QTestState *s, const char *fmt, ...);
+char *qtest_hmp(QTestState *s, const char *fmt, ...) GCC_FMT_ATTR(2, 3);
 
 /**
  * qtest_hmpv:
@@ -592,13 +592,13 @@ static inline QDict *qmp_eventwait_ref(const char *event)
 
 /**
  * hmp:
- * @fmt...: HMP command to send to QEMU
+ * @fmt...: HMP command to send to QEMU, formats arguments like sprintf().
  *
  * Send HMP command to QEMU via QMP's human-monitor-command.
  *
  * Returns: the command's output.  The caller should g_free() it.
  */
-char *hmp(const char *fmt, ...);
+char *hmp(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
 
 /**
  * get_irq:

tests/test-hmp.c

@@ -81,7 +81,7 @@ static void test_commands(void)
         if (verbose) {
             fprintf(stderr, "\t%s\n", hmp_cmds[i]);
         }
-        response = hmp(hmp_cmds[i]);
+        response = hmp("%s", hmp_cmds[i]);
         g_free(response);
     }
 
@@ -104,7 +104,7 @@ static void test_info_commands(void)
         if (verbose) {
             fprintf(stderr, "\t%s\n", info);
         }
-        resp = hmp(info);
+        resp = hmp("%s", info);
         g_free(resp);
         /* And move forward to the next line */
         info = strchr(endp + 1, '\n');