libsysprof-capture: add frame type for tracing

This is like sample but has an "enter/exit" flag with it. This can be
useful when you want to provide tracing instead of sampling. We use a
different frame type so that we can denote that this isn't traditional
sampling, and the flag can be used to find the next exit for the current
enter for calculating durations.

The entire stack trace is provided to make things easier on tools
which may want to deal with indirect functions that were not instrumented
but can be unwound. That may allow for tooling to give the user some
insight that it's not *just* this function entering, but some functions
before it were entered too.

This also adds a SysprofTracer instrument which will preload a
libsysprof-tracer-6.so into the process providing the
__cyg_profile_func_enter() and __cyg_profile_func_leave() hooks.

src/preload/meson.build

@@ -24,3 +24,10 @@ libsysprof_speedtrack_preload = shared_library('sysprof-speedtrack-@0@'.format(l
        install: true,
    install_dir: get_option('libdir'),
 )
+
+libsysprof_tracer_preload = shared_library('sysprof-tracer-@0@'.format(libsysprof_api_version),
+  ['sysprof-tracer-collector.c'],
+  dependencies: preload_deps,
+       install: true,
+   install_dir: get_option('libdir'),
+)

src/preload/sysprof-tracer-collector.c

@@ -28,6 +28,15 @@
 
 #include "gconstructor.h"
 
+#ifdef __GNUC__
+# define GNUC_CHECK_VERSION(major, minor) \
+    ((__GNUC__ > (major)) || \
+     ((__GNUC__ == (major)) && \
+      (__GNUC_MINOR__ >= (minor))))
+#else
+# define GNUC_CHECK_VERSION(major, minor) 0
+#endif
+
 #if defined (G_HAS_CONSTRUCTORS)
 # ifdef G_DEFINE_CONSTRUCTOR_NEEDS_PRAGMA
 #  pragma G_DEFINE_CONSTRUCTOR_PRAGMA_ARGS(collector_init_ctor)
@@ -49,24 +58,30 @@ collector_init_ctor (void)
   sysprof_collector_init ();
 }
 
-/* TODO:
- *
- * This is just an example.
- *
+/*
  * What we would really want to do is to have a new frame type for enter/exit
  * tracing so that we can only push/pop the new address to the sample. Then
- * when decoding it can recreate stack traces if necessary.
+ * when decoding it can recreate stack traces if necessary. But for now, we
+ * can emulate that by just adding a sample when we enter a function and
+ * leave a function. The rest could be done in post-processing.
  */
 
+#if GNUC_CHECK_VERSION(3,0)
+__attribute__((no_instrument_function))
+#endif
 void
 profile_func_enter (void *func,
                     void *call_site)
 {
-  sysprof_collector_sample (backtrace_func, NULL);
+  sysprof_collector_trace (backtrace_func, NULL, TRUE);
 }
 
+#if GNUC_CHECK_VERSION(3,0)
+__attribute__((no_instrument_function))
+#endif
 void
 profile_func_exit (void *func,
                    void *call_site)
 {
+  sysprof_collector_trace (backtrace_func, NULL, FALSE);
 }