[lttng-dev] [PATCH RFC v3 lttng-tools] New testpoint mechanism to instrument LTTng binaries for testing purpose
Mathieu Desnoyers
mathieu.desnoyers at efficios.com
Mon Sep 17 11:25:29 EDT 2012
* David Goulet (dgoulet at efficios.com) wrote:
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> Hoy,
>
> This looks good. However, I can _not_ merge it upstream for now. I
> will at least need a testpoint library example in the git tree to test
> it and make sure it does not break releases.
good point! We need at least one example user.
>
> Cheers!
> David
>
> Christian Babeux:
> > 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 */ +
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--
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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