[lttng-dev] lttng-ust with --std=c99 -pedantic
Mathieu Desnoyers
mathieu.desnoyers at efficios.com
Tue Jun 19 13:45:18 EDT 2012
* Mathieu Desnoyers (mathieu.desnoyers at efficios.com) wrote:
> * John Steele Scott (toojays at toojays.net) wrote:
> > On 13/06/12 01:25, Mathieu Desnoyers wrote:
> > > * Mathieu Desnoyers (mathieu.desnoyers at efficios.com) wrote:
> > >> Hi John,
> > >>
> > >> * John Steele Scott (toojays at toojays.net) wrote:
> > >>> I want to add lttng-ust tracepoints to a program which builds with "--std=c99 -pedantic". Right now this does not work.
> > >>>
> > >>> Using the demo program as an example, if you enable --std=c99, the first issue looks like:
> > >>>
> > >>> jscott at saaz:~/src/lttng-ust/tests/demo$ ccache gcc -std=c99 -DHAVE_CONFIG_H -I. -I../.. -I../../include/lttng -I../../include -Wall -g -O2 -MT demo.o -MD -MP -MF .deps/demo.Tpo -c -o demo.o demo.c
> > >>> In file included from demo.c:34:0:
> > >>> ust_tests_demo.h: In function ‘__tracepoint_cb_ust_tests_demo___starting’:
> > >>> ust_tests_demo.h:27:23: warning: implicit declaration of function ‘typeof’ [-Wimplicit-function-declaration]
> > >>> ust_tests_demo.h:27:218: error: expected ‘;’ before ‘_________p1’
> > >>> ust_tests_demo.h:27:395: error: ‘_________p1’ undeclared (first use in this function)
> > >>> ust_tests_demo.h:27:395: note: each undeclared identifier is reported only once for each function it appears in
> > >>> In file included from demo.c:34:0:
> > >>> ust_tests_demo.h: In function ‘__tracepoint_cb_ust_tests_demo___done’:
> > >>> ust_tests_demo.h:35:214: error: expected ‘;’ before ‘_________p1’
> > >>> ust_tests_demo.h:35:383: error: ‘_________p1’ undeclared (first use in this function)
> > >>> In file included from demo.c:35:0:
> > >>> ust_tests_demo2.h: In function ‘__tracepoint_cb_ust_tests_demo2___loop’:
> > >>> ust_tests_demo2.h:27:299: error: expected ‘;’ before ‘_________p1’
> > >>> ust_tests_demo2.h:27:470: error: ‘_________p1’ undeclared (first use in this function)
> > >>> In file included from demo.c:36:0:
> > >>> ust_tests_demo3.h: In function ‘__tracepoint_cb_ust_tests_demo3___done’:
> > >>> ust_tests_demo3.h:27:215: error: expected ‘;’ before ‘_________p1’
> > >>> ust_tests_demo3.h:27:386: error: ‘_________p1’ undeclared (first use in this function)
> > >>>
> > >>> This can be easily resolved by using __typeof__() instead of typeof(). Then I can build with --std=c99. But adding -pedantic still fails:
> > >> I pushed a fix for this:
> > >>
> > >> commit 6423c3134bf07d4a7db56f69f2c79b540a79c4f1
> > >> Author: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> > >> Date: Mon Jun 11 10:15:25 2012 -0400
> > >>
> > >> Fix c99 compatibility: use __typeof__ instead of typeof in public headers
> > >>
> > >> Reported-by: John Steele Scott <toojays at toojays.net>
> > >> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> > >>
> > >> I also had issues with (void) arg parameters with tracepoints, so
> > >> pushed:
> > >>
> > >> commit 4495dd39c05739d0fb2bc463b7c093d2459ce2b6
> > >> Author: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> > >> Date: Tue Jun 12 11:22:46 2012 -0400
> > >>
> > >> Fix: support -std=c99 in tracepoint macros
> > >>
> > >> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> > >>
> > >> I had also to fix userspace RCU library, with:
> > >>
> > >>
> > >> commit e51500edbd9919cee53bc85cbb4b22cd4786fc42
> > >> Author: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> > >> Date: Tue Jun 12 11:24:31 2012 -0400
> > >>
> > >> Fix c99 compatibility: use __asm__ and __volatile__ in public headers
> > >>
> > >> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> > >>
> > >> commit bdffa73aa208ad5f1e5b3a3cb6cbf86ac6996559
> > >> Author: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> > >> Date: Mon Jun 11 10:16:35 2012 -0400
> > >>
> > >> Fix c99 compatibility: use __typeof__ instead of typeof in public headers
> > >>
> > >> Reported-by: John Steele Scott <toojays at toojays.net>
> > >> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> > >>
> > >>
> > >>> jscott at saaz:~/src/lttng-ust/tests/demo$ ccache gcc -std=c99 -Dtypeof=__typeof__ -pedantic -DHAVE_CONFIG_H -I. -I../.. -I../../include/lttng -I../../include -Wall -g -O2 -MT demo.o -MD -MP -MF .deps/demo.Tpo -c -o demo.o demo.c
> > >>> In file included from ust_tests_demo.h:25:0,
> > >>> from demo.c:34:
> > >>> ../../include/lttng/tracepoint.h: In function ‘__tracepoints__init’:
> > >>> ../../include/lttng/tracepoint.h:251:4: warning: ISO C forbids conversion of object pointer to function pointer type [-pedantic]
> > >>> ../../include/lttng/tracepoint.h:255:4: warning: ISO C forbids conversion of object pointer to function pointer type [-pedantic]
> > >>> ../../include/lttng/tracepoint.h:260:4: warning: ISO C forbids conversion of object pointer to function pointer type [-pedantic]
> > >>> ../../include/lttng/tracepoint.h:264:4: warning: ISO C forbids conversion of object pointer to function pointer type [-pedantic]
> > >>> ../../include/lttng/tracepoint.h:268:4: warning: ISO C forbids conversion of object pointer to function pointer type [-pedantic]
> > >>> In file included from demo.c:34:0:
> > >>> ust_tests_demo.h: In function ‘__tracepoint_cb_ust_tests_demo___starting’:
> > >>> ust_tests_demo.h:27:161: warning: ISO C forbids braced-groups within expressions [-pedantic]
> > >>> ust_tests_demo.h:27:549: warning: ISO C forbids conversion of object pointer to function pointer type [-pedantic]
> > >>> In file included from demo.c:34:0:
> > >>> ust_tests_demo.h: In function ‘__tracepoint_cb_ust_tests_demo___done’:
> > >>> ust_tests_demo.h:35:161: warning: ISO C forbids braced-groups within expressions [-pedantic]
> > >>> ust_tests_demo.h:35:537: warning: ISO C forbids conversion of object pointer to function pointer type [-pedantic]
> > >>> In file included from demo.c:35:0:
> > >>> ust_tests_demo2.h: In function ‘__tracepoint_cb_ust_tests_demo2___loop’:
> > >>> ust_tests_demo2.h:27:245: warning: ISO C forbids braced-groups within expressions [-pedantic]
> > >>> ust_tests_demo2.h:27:624: warning: ISO C forbids conversion of object pointer to function pointer type [-pedantic]
> > >>> In file included from demo.c:36:0:
> > >>> ust_tests_demo3.h: In function ‘__tracepoint_cb_ust_tests_demo3___done’:
> > >>> ust_tests_demo3.h:27:161: warning: ISO C forbids braced-groups within expressions [-pedantic]
> > >>> ust_tests_demo3.h:27:540: warning: ISO C forbids conversion of object pointer to function pointer type [-pedantic]
> > >> I see these warnings, the only thing that currently fails is due to
> > >> BYTE_ORDER and BIG_ENDIAN not being defined. By adding:
> > >>
> > >> -DBYTE_ORDER=__BYTE_ORDER -DBIG_ENDIAN=__BIG_ENDIAN
> > >>
> > >> my tests/hello program, with a Makefile.am modified to do:
> > >>
> > >> hello_CFLAGS = -Werror=old-style-definition --std=c99 -pedantic
> > >>
> > >> prints many pedantic warnings, and fails with:
> > >>
> > >> ././ust_tests_hello.h:55:1: error: zero or negative size array ‘__event_fields___ust_tests_hello___tptest_sighandler’
> > >>
> > >> which seems to be caused by my event with 0 fields, which try to create
> > >> an array of length 0.
> > >>
> > >> I'll look into this one.
> > > Please try again with lttng-ust master HEAD, userspace-rcu master HEAD,
> > > and let me know if you experience problems compiling your instrumented
> > > application with --std=c99 -pedantic. Please note that the probe object
> > > (e.g. tp.c in the tests/hello program) needs to be compiled with gnu
> > > extensions, so you should not use --std=c99 for this specific object.
> >
> > Mathieu,
> >
> > Thanks for your reply, sorry it has taken me so long to respond.
> >
> > I can now build this application with userspace tracing. I was
> > actually able to compile the probe object with --std=c99 as well (this
> > time on Centos 6.2, didn't try yet on Ubuntu). Would you expect any
> > problems from this? I only have a single tracepoint in this app, but
> > it does seem to work.
>
> --std=c99 will not work to compile probes containing tracepoints taking
> 0 arguments. This is because c99 does not allow 0-sized arrays, and I
> don't want to complexify the probe generation to take care of this
> issue.
>
> >
> > 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.
>
> ------------------
>
> 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 <mathieu.desnoyers at efficios.com>
> 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 <mathieu.desnoyers at efficios.com>
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 <mathieu.desnoyers at efficios.com>
>
> Thanks!
>
> Mathieu
>
>
>
> >
> > cheers,
> >
> > John
> >
> > _______________________________________________
> > lttng-dev mailing list
> > lttng-dev at lists.lttng.org
> > http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
>
> --
> Mathieu Desnoyers
> Operating System Efficiency R&D Consultant
> EfficiOS Inc.
> http://www.efficios.com
>
> _______________________________________________
> lttng-dev mailing list
> lttng-dev at lists.lttng.org
> http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
--
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
More information about the lttng-dev
mailing list