[PATCH 1/2] trace-cmd: libtracecmd: Fixing linking to C++ code

[PATCH 1/2] trace-cmd: libtracecmd: Fixing linking to C++ code

[Joel Fernandes (Google)]

Linking in C++ compilers (including g++) causes references to be created
with their arguments. Due to this, trace library headers included into
C++ code base will cause their objects to built with symbols with
arguments. Apparently this is to support operator overloading in C++.

This causes linker errors. For example, here's what I get when I try to
link libtracecmd with a main.o built from a C++ main.cc source file.

 main.cc:(.text+0x90):
	undefined reference to `tracecmd_get_tep(tracecmd_input*)'
	undefined reference to `tracecmd_free_record(tep_record*)'
	undefined reference to `tracecmd_read_data(tracecmd_input*, int)'

The standard fix for this is to wrap the C project's header in
extern "C".

With this patch, I am able to link libtracecmd into a C++
code base.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 include/trace-cmd/trace-cmd.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/include/trace-cmd/trace-cmd.h b/include/trace-cmd/trace-cmd.h
index 4963f45..b050233 100644
--- a/include/trace-cmd/trace-cmd.h
+++ b/include/trace-cmd/trace-cmd.h
@@ -9,6 +9,10 @@
 #include "event-parse.h"
 #include "tracefs.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 struct tracecmd_input;
 
 enum tracecmd_open_flags {
@@ -78,5 +82,8 @@ struct tracecmd_filter *tracecmd_filter_add(struct tracecmd_input *handle,
 					    const char *filter_str, bool neg);
 enum tracecmd_filters tracecmd_filter_match(struct tracecmd_filter *filter,
 					    struct tep_record *record);
+#ifdef __cplusplus
+}
+#endif
 
 #endif /* _TRACE_CMD_H */
-- 
2.25.1

[PATCH 2/2] trace-cmd: README: Add note on installing libtracecmd

[Joel Fernandes (Google)]

This might be obvious but it still took me some Makefile reading. Add it
to README to make it easier for others.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 README | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/README b/README
index 9d8c127..e823843 100644
--- a/README
+++ b/README
@@ -57,6 +57,9 @@ To install trace-cmd
 To install the gui
     make install_gui
 
+To install libtracecmd libraries
+    make install_libs
+
 Note: The default install is relative to /usr/local
     The default install directory is /usr/local/bin
     The default plugin directory is /usr/local/lib/trace-cmd/plugins
-- 
2.25.1

Re: [PATCH 2/2] trace-cmd: README: Add note on installing libtracecmd

[Steven Rostedt]

On Sun, 14 Aug 2022 23:13:42 -0400
"Joel Fernandes (Google)" <joel@joelfernandes.org> wrote:

> This might be obvious but it still took me some Makefile reading. Add it
> to README to make it easier for others.
> 
> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>

Both patches applied. Thanks Joel!

-- Steve

> ---
>  README | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/README b/README
> index 9d8c127..e823843 100644
> --- a/README
> +++ b/README
> @@ -57,6 +57,9 @@ To install trace-cmd
>  To install the gui
>      make install_gui
>  
> +To install libtracecmd libraries
> +    make install_libs
> +
>  Note: The default install is relative to /usr/local
>      The default install directory is /usr/local/bin
>      The default plugin directory is /usr/local/lib/trace-cmd/plugins

Re: [PATCH 2/2] trace-cmd: README: Add note on installing libtracecmd

[Joel Fernandes]

On 9/21/2022 9:43 PM, Steven Rostedt wrote:
> On Sun, 14 Aug 2022 23:13:42 -0400
> "Joel Fernandes (Google)" <joel@joelfernandes.org> wrote:
> 
>> This might be obvious but it still took me some Makefile reading. Add it
>> to README to make it easier for others.
>>
>> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> 
> Both patches applied. Thanks Joel!

Thanks!

 - Joel