Re: [PATCH v2 3/9] kernel-shark: Fix KS_DEFINE_PLUGIN_CONTEXT macro

Yordan Karadzhov <y.karadz@xxxxxxxxx> · Mon, 10 May 2021 14:53:08 +0300

On 6.05.21 г. 21:11, Steven Rostedt wrote:

On Wed, 28 Apr 2021 16:47:24 +0300
"Yordan Karadzhov (VMware)" <y.karadz@xxxxxxxxx> wrote:


The KS_DEFINE_PLUGIN_CONTEXT macro implements methods that are used
to deal with plugin-specific context objects. However, when this macro
is used in multiple plugins and those plugins are loaded together
the symbol resolving fails, resulting in undefined behavior. Namely,
version of the function from one plugin, being called by another
plugin. Here we make sure that the methods defined in
KS_DEFINE_PLUGIN_CONTEXT are not visible outside of the corresponding
plugin.

Fixing: 15df009 (kernel-shark: Add KS_DEFINE_PLUGIN_CONTEXT macro)
Signed-off-by: Yordan Karadzhov (VMware) <y.karadz@xxxxxxxxx>
---
  src/libkshark-plugin.h     | 22 ++++++++++++++++++----
  src/plugins/sched_events.c |  3 +++
  src/plugins/sched_events.h |  3 +--
  3 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/src/libkshark-plugin.h b/src/libkshark-plugin.h
index c110616..752dbeb 100644
--- a/src/libkshark-plugin.h
+++ b/src/libkshark-plugin.h
@@ -24,6 +24,8 @@ extern "C" {
  /* Quiet warnings over documenting simple structures */
  //! @cond Doxygen_Suppress

  

+#define __hidden __attribute__((visibility ("hidden")))

+
  #define _MAKE_STR(x)	#x

  

  #define MAKE_STR(x)	_MAKE_STR(x)

@@ -364,11 +366,14 @@ int kshark_handle_all_dpis(struct kshark_data_stream *stream,
  	__ok;								\
  })									\

  

-/** General purpose macro defining methods for adding plugin context. */

+/**
+ * General purpose macro defining methods for adding plugin context.
+ * Do not use this macro in header files.
+ */
  #define KS_DEFINE_PLUGIN_CONTEXT(type)					\
  static type **__context_handler;					\
  static ssize_t __n_streams = -1;					\
-static inline type *__init(int sd)					\
+__hidden type *__init(int sd)						\


This is strange, because static inline should never be a problem in this
regard (otherwise things will break elsewhere too).

static is never exported (it's stronger than "hidden").

Can you show me how you see this error, because this solution does not make
any sense.



The problem is that some plugins can build from multiple source files. 

For example in the case when part of the plugin is written in C and 

another part in C++. In those cases we cannot have the functions being 

static.


Thanks!
Yordan




-- Steve




