On Tue, Sep 20, 2011 at 5:22 PM, Mathieu Desnoyers <comp...@krystal.dyndns.org> wrote: > * Stefan Hajnoczi (stefa...@gmail.com) wrote: >> 2011/9/20 Mathieu Desnoyers <comp...@krystal.dyndns.org>: >> > * Lluís Vilanova (vilan...@ac.upc.edu) wrote: >> >> Stefan Hajnoczi writes: >> >> >> >> > On Fri, Sep 16, 2011 at 06:59:38PM +0200, Lluís Vilanova wrote: >> >> >> Signed-off-by: Lluís Vilanova <vilan...@ac.upc.edu> >> >> >> --- >> >> >> trace-events | 4 ++-- >> >> >> 1 files changed, 2 insertions(+), 2 deletions(-) >> >> >> >> >> >> diff --git a/trace-events b/trace-events >> >> >> index 9d1fbbb..b653d70 100644 >> >> >> --- a/trace-events >> >> >> +++ b/trace-events >> >> >> @@ -418,8 +418,8 @@ milkymist_pfpu_pulse_irq(void) "Pulse IRQ" >> >> >> # hw/milkymist-softusb.c >> >> >> milkymist_softusb_memory_read(uint32_t addr, uint32_t value) "addr >> >> >> %08x value %08x" >> >> >> milkymist_softusb_memory_write(uint32_t addr, uint32_t value) "addr >> >> >> %08x value %08x" >> >> >> -milkymist_softusb_mevt(uint8_t m) "m %d" >> >> >> -milkymist_softusb_kevt(uint8_t m) "m %d" >> >> >> +milkymist_softusb_mevt(uint8_t _m) "m %d" >> >> >> +milkymist_softusb_kevt(uint8_t _m) "m %d" >> >> >> >> > The LTTng community has been very responsive in addressing namespace >> >> > issues with libust. Let's post more details and see if it can be fixed >> >> > in libust. >> >> >> >> > Could you please post your gcc and libust versions? >> >> >> >> > I have not been able to reproduce the problem on Debian libust-dev >> >> > 0.15-3. My gcc version is Debian gcc 4.6.1-4. >> >> >> >> Yup, I was using libust-dev 0.5 (debian stable). After switching to 0.15 >> >> (debian >> >> testing) other problems arise. >> >> >> >> For example, in my box compiling osdep.c yields lots of "variable >> >> ‘__tp_cb_data’ >> >> set but not used", but using a minimal example does not raise such >> >> problems, so >> >> I'm assuming this is related to some namespace problems related to some >> >> other >> >> code in qemu's headers. >> > >> > If you can find a few minutes to provide: >> > >> > 1) a link to the git repository/commit ID you are testing >> > 2) the exact configuration you use (detailed way to reproduce the >> > problem, as a sequence of commands from a pristine repository) >> > >> > It will allow me to look into this warning and fix it. >> >> AFAICT the only problem with libust is the __tp_cb_data set but not >> used warning that gcc 4.6 emits, see my test program: >> >> #include <stdint.h> >> #include <ust/tracepoint.h> >> >> DECLARE_TRACE(ust_milkymist_softusb_mevt, TP_PROTO(uint8_t m), >> TP_ARGS(m)); >> >> int main(int argc, char **argv) >> { >> return 0; >> } >> >> You will get an error with gcc 4.6 and libust 0.15: >> >> $ gcc -o a -Wall a.c > > Ah, I see. This is due to the backward compatibility API I added in > 0.15 for qemu. It skips using the __tp_cb_data private data. So it does > make sense that the compiler complains about this. I can add a > __attribute__((unused)), as proposed by Lluís. > >> >> QEMU itself does have one problem with libust 0.15. We do >> DECLARE_TRACE(name, TP_PROTO(void), TP_ARGS()). This results in a >> compiler error but we can fix this my changing our tracepoints to use >> DECLARE_TRACE(name, TP_PROTO(), TP_ARGS()) I think. Perhaps libust's >> behavior here has changed, it shouldn't be hard to update QEMU's >> tracetool tracepoint generator though. > > For tracepoints without arguments, you need to use something like: > > TRACEPOINT_EVENT_NOARGS(name, TP_FIELDS()) > > (note: the full support of TP_FIELDS() declaration will come in UST 2.0. > For UST 0.15, it's just ignored) > > The _NOARGS variant lets you handle the (void) 0 parameter case.
Okay, this is the fault of QEMU's tracetool script, which generates the LTTng UST tracepoints. We can move to the new TRACEPOINT*() macros and use _NOARGS as appropriate. Stefan