On 20/06/12 03:15, Mathieu Desnoyers wrote: > * Mathieu Desnoyers ([email protected]) wrote: >> * John Steele Scott ([email protected]) wrote: >> snip snip >>> The thing I forgot to mention is: okay, I can build now with >>> -pedantic, but I can't build with "-pedantic -Werror". This >>> application builds with "--std=c99 -pedantic -Werror" (among many >>> other flags). I can of course remove -Werror for my tests, but in the >>> longer term I would like to see lttng-ust enabled in our regular >>> build, and disabling -Werror for that is not something we want to do. >>> If I only had to disable it for the trace provider, I could negotiate >>> that, but disabling it for any module which uses tracepoints is >>> undesirable. >>> >>> I haven't yet looked at how difficult it would be do eliminate these >>> pedantic warnings. Do you have a feel for what is involved? >>> Preprocessor tricks warp my mind. :( >> I don't think we'll want to make the lttng probe module build under >> --std=c99 -pedandic -Werror, but I think we should focus on making sure >> the tracepoint part that is built within the application (with >> TRACEPOINT_CREATE_PROBES _not_ defined) builds fine in --std=c99 >> -pedantic. >> >> Currently, building a simple test program with tracepoints under >> --std=c99 -pedantic gets me: >> >> >> In file included from ust_tests_hello.h:25:0, >> from hello.c:34: >> ../../include/lttng/tracepoint.h: In function ‘__tracepoints__init’: >> ../../include/lttng/tracepoint.h:261:3: warning: ISO C forbids conversion of >> object pointer to function pointer type [-pedantic] >> ../../include/lttng/tracepoint.h:265:3: warning: ISO C forbids conversion of >> object pointer to function pointer type [-pedantic] >> ../../include/lttng/tracepoint.h:270:3: warning: ISO C forbids conversion of >> object pointer to function pointer type [-pedantic] >> ../../include/lttng/tracepoint.h:274:3: warning: ISO C forbids conversion of >> object pointer to function pointer type [-pedantic] >> ../../include/lttng/tracepoint.h:278:3: warning: ISO C forbids conversion of >> object pointer to function pointer type [-pedantic] >> >> ---> see include/lttng/tracepoint.h __tracepoints__init(): >> ----> This is caused by use of dlsym() to lookup a function pointer from >> a symbol. dlsym() returns "void *", and we cast it into function >> pointer type. Ideas on how to make this c99 pedantic compliant are >> welcome.
I found this warning discussed in a GCC bug report. Jakub Jelinek's suggestion at http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45289#c6 (load the result of dlsym into a void *, then memcpy to the function pointer), does make these go away (using GCC 4.4.6 on Centos 6.2). >> >> ------------------ >> >> In file included from hello.c:34:0: >> ust_tests_hello.h: In function ‘__tracepoint_cb_ust_tests_hello___tptest’: >> ust_tests_hello.h:28:1: warning: ISO C forbids braced-groups within >> expressions [-pedantic] >> ust_tests_hello.h:28:1: warning: ISO C forbids conversion of object pointer >> to function pointer type [-pedantic] >> ust_tests_hello.h: In function >> ‘__tracepoint_cb_ust_tests_hello___tptest_sighandler’: >> ust_tests_hello.h:52:1: warning: ISO C forbids braced-groups within >> expressions [-pedantic] >> ust_tests_hello.h:52:1: warning: ISO C forbids conversion of object pointer >> to function pointer type [-pedantic] >> >> ---> see include/lttng/tracepoint.h >> >> #define _DECLARE_TRACEPOINT(_provider, _name, ...) >> \ >> extern struct tracepoint __tracepoint_##_provider##___##_name; >> \ >> static inline void >> __tracepoint_cb_##_provider##___##_name(_TP_ARGS_PROTO(__VA_ARGS__)) \ >> [...] >> >> ----> this is caused by use of "tp_rcu_dereference_bp()", which is >> defined in include/lttng/tracepoint-rcu.h (in the #else clause) : >> >> #define tp_rcu_dereference_bp(p) >> \ >> ({ >> \ >> __typeof__(p) _________p1 = URCU_FORCE_CAST(__typeof__(p), >> \ >> >> tracepoint_dlopen.rcu_dereference_sym_bp(URCU_FORCE_CAST(void *, p))); \ >> (_________p1); >> \ >> }) >> >> For this one, we should be able to change it into a single-expression >> and remove the braced-groups, since we are just really evaluating a >> single expression here. Fixed by the following commit in lttng-ust >> master: >> >> commit a4eaf8eabe829be8f7d7432ffaf83291a068b0ed >> Author: Mathieu Desnoyers <[email protected]> >> Date: Mon Jun 18 10:10:36 2012 -0400 >> >> Fix c99 compatibility: tp_rcu_dereference_bp() should not use >> braced-groups within expressions >> >> ------------------ >> >> hello.c: In function ‘inthandler’: >> hello.c:39:47: warning: ISO C99 requires rest arguments to be used [enabled >> by default] >> ---> see include/lttng/tracepoint.h tracepoint() macro. >> ----> this is caused by not passing any argument to the tracepoint. >> Ideas on how to fix this are welcome, as I don't see any way to do it in >> C99-pedantic. > I think I found a way to fix the last pedantic warnings. Can you try > with this master branch commit ? > > > commit fbdeb5ecb8ff9b7d73a72de9fc66d07f7797d93f > Author: Mathieu Desnoyers <[email protected]> > Date: Tue Jun 19 13:45:05 2012 -0400 > > Fix C99 strict compatibility: don't use void * for function pointers > > compiling public headers with --std=x99 -pedantic shows: > > warning: ISO C forbids conversion of object pointer to function pointer > type > > Use "void (*func)(void)" to represent a generic function pointer rather > than "void *". > > Signed-off-by: Mathieu Desnoyers <[email protected]> > Unfortunately, this isn't sufficient to fix these warnings on Centos 6.2. However, I can now make the warnings go away by using dlsym+memcpy (instead of dlsym+cast), as mentioned above. I haven't had a chance to actually use the resulting binary yet, but I don't see why it shouldn't work. Thanks, John _______________________________________________ lttng-dev mailing list [email protected] http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
