[lttng-dev] [PATCH RFC v3 lttng-tools] New testpoint mechanism to instrument LTTng binaries for testing purpose
Christian Babeux
christian.babeux at efficios.com
Fri Sep 14 15:00:30 EDT 2012
This commit introduce two new macros: TESTPOINT_DECL(name) and
testpoint(name).
Here a quick example that show how to use the testpoint mechanism:
file: main.c
/* Testpoint declaration */
TESTPOINT_DECL(interesting_function)
void interesting_function(void)
{
testpoint(interesting_function);
/* Some processing that can fail */
...
}
int main(int argc, char *argv[])
{
interesting_function();
...
printf("End");
}
file: testpoint.c
void __testpoint_interesting_function(void)
{
printf("In testpoint of interesting function!");
}
Compile:
gcc -o test main.c
gcc -fPIC -shared -o testpoint.so testpoint.c
Run:
> ./test
End
> export LTTNG_TESTPOINT_ENABLE=1
> LD_PRELOAD=testpoint.so ./test
In testpoint of interesting function!
End
> export LTTNG_TESTPOINT_ENABLE=0
> LD_PRELOAD=testpoint.so ./test
End
The testpoint mechanism is triggered via the preloading of a shared
object containing the appropriate testpoint symbols and by setting the
LTTNG_TESTPOINT_ENABLE environment variable.
The check on this environment variable is done on the application startup
with the help of a constructor (lttng_testpoint_check) which toggle a global
state variable indicating whether or not the testpoints should be activated.
When enabled, the testpoint() macro calls an underlying wrapper specific to
the testpoint and simply try to lookup the testpoint symbol via a dlsym()
call.
When disabled, the testpoint() call will only incur an additionnal test
per testpoint on a global variable. This performance 'hit' should be
acceptable for production use.
The testpoint mechanism should be *always on*. It can be explicitly
disabled via CFLAGS="-DNTESTPOINT" in a way similar to NDEBUG and assert().
Signed-off-by: Christian Babeux <christian.babeux at efficios.com>
---
configure.ac | 1 +
src/common/Makefile.am | 2 +-
src/common/testpoint/Makefile.am | 6 ++++
src/common/testpoint/testpoint.c | 64 ++++++++++++++++++++++++++++++++++
src/common/testpoint/testpoint.h | 74 ++++++++++++++++++++++++++++++++++++++++
5 files changed, 146 insertions(+), 1 deletion(-)
create mode 100644 src/common/testpoint/Makefile.am
create mode 100644 src/common/testpoint/testpoint.c
create mode 100644 src/common/testpoint/testpoint.h
diff --git a/configure.ac b/configure.ac
index 7687280..8e61115 100644
--- a/configure.ac
+++ b/configure.ac
@@ -275,6 +275,7 @@ AC_CONFIG_FILES([
src/common/sessiond-comm/Makefile
src/common/compat/Makefile
src/common/relayd/Makefile
+ src/common/testpoint/Makefile
src/lib/Makefile
src/lib/lttng-ctl/Makefile
src/lib/lttng-ctl/filter/Makefile
diff --git a/src/common/Makefile.am b/src/common/Makefile.am
index ca48153..889b04e 100644
--- a/src/common/Makefile.am
+++ b/src/common/Makefile.am
@@ -1,6 +1,6 @@
AM_CPPFLAGS =
-SUBDIRS = compat hashtable kernel-ctl sessiond-comm relayd kernel-consumer ust-consumer
+SUBDIRS = compat hashtable kernel-ctl sessiond-comm relayd kernel-consumer ust-consumer testpoint
AM_CFLAGS = -fno-strict-aliasing
diff --git a/src/common/testpoint/Makefile.am b/src/common/testpoint/Makefile.am
new file mode 100644
index 0000000..7d3df16
--- /dev/null
+++ b/src/common/testpoint/Makefile.am
@@ -0,0 +1,6 @@
+AM_CPPFLAGS =
+
+noinst_LTLIBRARIES = libtestpoint.la
+
+libtestpoint_la_SOURCES = testpoint.h testpoint.c
+libtestpoint_la_LIBADD = -ldl
diff --git a/src/common/testpoint/testpoint.c b/src/common/testpoint/testpoint.c
new file mode 100644
index 0000000..3d01a03
--- /dev/null
+++ b/src/common/testpoint/testpoint.c
@@ -0,0 +1,64 @@
+/*
+ * Copyright (C) 2012 - Christian Babeux <christian.babeux at efficios.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License, version 2 only,
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef NTESTPOINT
+
+#define _GNU_SOURCE /* for RTLD_DEFAULT GNU extension */
+
+#include <dlfcn.h> /* for dlsym */
+#include <stdlib.h> /* for getenv */
+#include <string.h> /* for strncmp */
+
+#include "testpoint.h"
+
+/* Environment variable used to enable the testpoints facilities. */
+static const char *lttng_testpoint_env_var = "LTTNG_TESTPOINT_ENABLE";
+
+/* Testpoint toggle flag */
+int lttng_testpoint_activated;
+
+/*
+ * Toggle the support for testpoints on the application startup.
+ */
+static void __attribute__((constructor)) lttng_testpoint_check(void)
+{
+ char *testpoint_env_val = NULL;
+
+ testpoint_env_val = getenv(lttng_testpoint_env_var);
+ if (testpoint_env_val != NULL
+ && (strncmp(testpoint_env_val, "1", 1) == 0)) {
+ lttng_testpoint_activated = 1;
+ }
+}
+
+/*
+ * Lookup a symbol by name.
+ *
+ * Return the address where the symbol is loaded
+ * or NULL if the symbol was not found.
+ */
+void *lttng_testpoint_lookup(const char *name)
+{
+ if (!name) {
+ return NULL;
+ }
+
+ return dlsym(RTLD_DEFAULT, name);
+}
+
+#endif /* NTESTPOINT */
+
diff --git a/src/common/testpoint/testpoint.h b/src/common/testpoint/testpoint.h
new file mode 100644
index 0000000..2925b0a
--- /dev/null
+++ b/src/common/testpoint/testpoint.h
@@ -0,0 +1,74 @@
+/*
+ * Copyright (C) 2012 - Christian Babeux <christian.babeux at efficios.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License, version 2 only,
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifdef NTESTPOINT
+
+#define testpoint(name)
+#define TESTPOINT_DECL(name)
+
+#else /* NTESTPOINT */
+
+#include <urcu.h> /* for caa_likely/unlikely */
+
+extern int lttng_testpoint_activated;
+
+void *lttng_testpoint_lookup(const char *name);
+
+/*
+ * Testpoint is only active if the global
+ * lttng_testpoint_activated flag is set.
+ */
+#define testpoint(name) \
+ do { \
+ if (caa_unlikely(lttng_testpoint_activated)) { \
+ __testpoint_##name##_wrapper(); \
+ } \
+ } while (0)
+
+/*
+ * One wrapper per testpoint is generated. This is to keep track
+ * of the symbol lookup status and the corresponding function
+ * pointer, if any.
+ */
+#define _TESTPOINT_DECL(_name) \
+ static inline void __testpoint_##_name##_wrapper(void) \
+ { \
+ static void (*tp)(void); \
+ static int found; \
+ const char *tp_name = "__testpoint_" #_name; \
+ \
+ if (tp) { \
+ tp(); \
+ } else { \
+ if (!found) { \
+ tp = lttng_testpoint_lookup(tp_name); \
+ if (tp) { \
+ found = 1; \
+ tp(); \
+ } else { \
+ found = -1; \
+ } \
+ } \
+ } \
+ }
+
+/* Testpoint declaration */
+#define TESTPOINT_DECL(name) \
+ _TESTPOINT_DECL(name)
+
+#endif /* NTESTPOINT */
+
--
1.7.11.4
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