Re: [lttng-dev] [PATCH] Fix: tracepoint.h: define SDT_USE_VARIADIC in pkg-config CFLAGS

[Michael Jeanson via lttng-dev <lttng-dev@lists.lttng.org>]

Hi Stefan,

I proposed a patch here[1] that addresses this problem in a generic way by
duplicating the macro and namespacing it under LTTNG_. Honestly this is more
of an sdt bug, the STAP_PROBEV should be in it's own include guard outside
of _SYS_SDT_H or in it's own header file but we have to work with what's there.

Can you have a look at the patch and confirm that it fixes your problem?

Cheers,

Michael

[1] https://review.lttng.org/c/lttng-ust/+/3685 


----- On 24 Jun, 2020, at 12:09, lttng-dev lttng-dev@lists.lttng.org wrote:

> LTTng Userspace Tracer 2.11 with sdt enabled can break builds of
> applications that include <sys/sdt.h> themselves. QEMU
> (https://qemu.org/) is one example.
> 
> When applications include <sys/sdt.h> themselves before LTTng Userspace
> Tracer header files and the SDT_USE_VARIADIC macro is not defined,
> compilation fails due to the absense of STAP_PROBEV() macro that LTTng
> Userspace Tracer requires.
> 
> Define SDT_USE_VARIADIC in the pkg-config file so that all compilation
> units that use LTTng Userspace Tracer are guaranteed to have the macro
> defined even if <sys/sdt.h> is included elsewhere before LTTng Userspace
> Tracer header files.
> 
> In other words, define SDT_USE_VARIADIC on the compiler command-line
> instead of in <lttng/tracepoint.h>. This way it will always been defined
> when <sys/sdt.h> is included.
> 
> Make sure to define SDT_USE_VARIADIC when <lttng/tracepoint.h> is
> included without it. This happens when applications do not use
> pkg-config.
> 
> Fixes: b2f60c7986bb69f81b79b68f1bfe83aafa3278a7 ("Add sdt.h integration")
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
> Warning: this patch doesn't work yet. SDT_CFLAGS also needs to be passed
> into LTTng Userspace Tracer's own CFLAGS so that compilation can
> succeed. I don't know the autoconf/automake syntax to do this and wanted
> to see what you think of this solution before investing more time.
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