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

* [PATCH 1/2] trace-cmd: libtracecmd: Fixing linking to C++ code
@ 2022-08-15  3:13 Joel Fernandes (Google)
  2022-08-15  3:13 ` [PATCH 2/2] trace-cmd: README: Add note on installing libtracecmd Joel Fernandes (Google)
  0 siblings, 1 reply; 4+ messages in thread
From: Joel Fernandes (Google) @ 2022-08-15  3:13 UTC (permalink / raw)
  To: linux-trace-devel; +Cc: rostedt, 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


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