Let's assume I'm trying to instrument glibc. Making glibc is tricky by
itself, but the following works under Ubuntu 14.04 and glibc 2.15 (obtained
from ftp.gnu.org/gnu/glibc/). I have deployed glibc-2.15.tar.gz to a local
./glibc-2.15 folder and created a sibling ./glibc-build folder:
glibc-build$ ../glibc-2.15/configure CFLAGS="-O2 -U_FORTIFY_SOURCE
-fno-stack-protector" --prefix=/home/<user>/<path>/usr-local
--with-pkgversion=user-glibc &> configure.log
glibc-build$ make &> make.log
Now I take a "simple" glibc service, such as printf
(glibc-2.15/stdio-common/printf.c), and try to instrument it. I modify
printf.c like this:
#include <libioP.h>
#include <stdarg.h>
#include <stdio.h>
//THREE NEW LINES
#define TRACEPOINT_DEFINE
#define TRACEPOINT_PROBE_DYNAMIC_LINKAGE
#include "printf-tp.h"
#undef printf
/* Write formatted output to stdout from the format string FORMAT. */
/* VARARGS1 */
int
__printf (const char *format, ...)
{
va_list arg;
int done;
//ONE NEW LINE
tracepoint(libc_tracer, printf);
va_start (arg, format);
done = vfprintf (stdout, format, arg);
va_end (arg);
return done;
}
The tracepoint is a simple one.
glibc-2.15/stdio-common/printf-tp.c :
#define TRACEPOINT_CREATE_PROBES
#include "printf-tp.h"
glibc-2.15/stdio-common/printf-tp.h :
<usual preface>
TRACEPOINT_EVENT(
libc_tracer,
printf,
TP_ARGS(),
TP_FIELDS()
)
TRACEPOINT_LOGLEVEL(
libc_tracer,
printf,
TRACE_INFO)
<usual postface>
This is then compiled manually in place:
glibc-2.15/stdio-common$ gcc -I. -fPIC -c -o libprintf-tp.o printf-tp.c
glibc-2.15/stdio-common$ gcc -shared -Wl,-soname,libprintf-tp.so.1
-Wl,-no-as-needed -o libprintf-tp.so.1.0 -L/usr/local/lib -llttng-ust
libprintf-tp.o
glibc-2.15/stdio-common$ ln -sf libprintf-tp.so.1.0 libprintf-tp.so.1
glibc-2.15/stdio-common$ ln -sf libprintf-tp.so.1 libprintf-tp.so
Pretty standard so far (using LTTng 2.3.0).
The goal is to run apps from the instrumented glibc (libc.so.6) by
LD_PRELOADing it (or installing it as the standard glibc) that become
LTTng-active (provide user-space events) if the tracepoint provider shared
object is also preloaded. This is similar to the standard dynamically-loaded
statically-unaware approach to app instrumentation, where the instrumented app
runs fine without the tracepoint provider shared object, and becomes
LTTng-active only if the latter is preloaded.
The glibc make doesn't like this, however. It fails with a bunch of
undefined references to dlsym, dlopen, dlclose (in __tracepoint__init_urcu_sym,
__tracepoints__init, __tracepoints__ptrs_init, __tracepoints__destroy,
__tracepoints__ptrs_destroy) when it tries to use libc_pic.os in the final(?)
construction of libc.so. (I can provide the make log, of course)
Anybody else tried to do something like this? What is the least intrusive
way of getting an LTTng-instrumented libc.so to compile?
Daniel U. Thibault
Protection des systèmes et contremesures (PSC) | Systems Protection &
Countermeasures (SPC)
Cyber sécurité pour les missions essentielles (CME) | Mission Critical Cyber
Security (MCCS)
RDDC - Centre de recherches de Valcartier | DRDC - Valcartier Research Centre
2459 route de la Bravoure
Québec QC G3J 1X5
CANADA
Vox : (418) 844-4000 x4245
Fax : (418) 844-4538
NAC : 918V QSDJ <http://www.travelgis.com/map.asp?addr=918V%20QSDJ>
Gouvernement du Canada | Government of Canada
<http://www.valcartier.drdc-rddc.gc.ca/>
LinkedIn: <http://ca.linkedin.com/in/daniel-u-thibault/>
Research Gate: <https://www.researchgate.net/profile/Daniel_Thibault/>
_______________________________________________
lttng-dev mailing list
[email protected]
http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
