[Spice-devel] [spice-common v3] log: Let gcc know about the logging macros which abort

[Christophe Fergeau]

This commit adds a SPICE_UNREACHABLE macro (courtesy of Frediano)
so that gcc does not think that code control can go past
spice_return_{val_,}if_fail(), spice_critical() and spice_error()

This avoids this kind of warnings:

fallthrough.c:

 #include "log.h"

int main(int argc, char **argv)
{
    switch(argc) {
        case 1:
            spice_critical("foo");
       default:
            return 0;
    }
}

$ gcc  -c    $(pkg-config --cflags --libs glib-2.0 spice-protocol)
       -I common   -Wimplicit-fallthrough=5 ./fallthrough.c
In file included from ./fallthrough.c:1:
./fallthrough.c: In function 'main':
common/log.h:73:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
   73 |     spice_log(G_LOG_LEVEL_CRITICAL, SPICE_STRLOC, __FUNCTION__, "" format, ## __VA_ARGS__); \
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./fallthrough.c:8:25: note: in expansion of macro 'spice_critical'
    8 |                         spice_critical("foo");
      |                         ^~~~~~~~~~~~~~
./fallthrough.c:9:17: note: here
    9 |                 default:
      |                 ^~~~~~~

Signed-off-by: Christophe Fergeau <cfergeau at redhat.com>
---
Maybe a bit too much for a single commit, I can split :)

 common/log.h    | 8 ++++++--
 common/macros.h | 8 ++++++++
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/common/log.h b/common/log.h
index 7c67e7a..201c87a 100644
--- a/common/log.h
+++ b/common/log.h
@@ -39,16 +39,18 @@ void spice_log(GLogLevelFlags log_level,
                const char *format,
                ...) G_GNUC_PRINTF(4, 5);
 
+/* FIXME: name is misleading, this aborts.. */
 #define spice_return_if_fail(x) G_STMT_START {                          \
     if G_LIKELY(x) { } else {                                           \
-        spice_log(G_LOG_LEVEL_CRITICAL, SPICE_STRLOC, G_STRFUNC, "condition `%s' failed", #x); \
+        spice_critical("condition `%s' failed", #x);                    \
         return;                                                         \
     }                                                                   \
 } G_STMT_END
 
+/* FIXME: name is misleading, this aborts.. */
 #define spice_return_val_if_fail(x, val) G_STMT_START {                 \
     if G_LIKELY(x) { } else {                                           \
-        spice_log(G_LOG_LEVEL_CRITICAL, SPICE_STRLOC, __FUNCTION__, "condition `%s' failed", #x); \
+        spice_critical("condition `%s' failed", #x);                    \
         return (val);                                                   \
     }                                                                   \
 } G_STMT_END
@@ -71,10 +73,12 @@ void spice_log(GLogLevelFlags log_level,
 
 #define spice_critical(format, ...) G_STMT_START {                          \
     spice_log(G_LOG_LEVEL_CRITICAL, SPICE_STRLOC, __FUNCTION__, "" format, ## __VA_ARGS__); \
+    SPICE_UNREACHABLE;                                                                      \
 } G_STMT_END
 
 #define spice_error(format, ...) G_STMT_START {                         \
     spice_log(G_LOG_LEVEL_ERROR, SPICE_STRLOC, __FUNCTION__, "" format, ## __VA_ARGS__); \
+    SPICE_UNREACHABLE;                                                                   \
 } G_STMT_END
 
 #define spice_warn_if_fail(x) G_STMT_START {            \
diff --git a/common/macros.h b/common/macros.h
index 2f24ada..92cd82c 100644
--- a/common/macros.h
+++ b/common/macros.h
@@ -55,4 +55,12 @@
 
 #define SPICE_VERIFY(cond) verify_expr(cond, (void)1)
 
+#if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 5)
+#define SPICE_UNREACHABLE __builtin_unreachable()
+#elif defined(_MSC_VER)
+#define SPICE_UNREACHABLE __assume(0)
+#else
+#define SPICE_UNREACHABLE for(;;) continue
+#endif
+
 #endif // H_SPICE_COMMON_MACROS
-- 
2.21.0