On 06/17/2012 05:08 PM, Lars wrote:
Hello,
I have recently started to use LTTng-UST and am using LD_PRELOAD
to make it possilbe to execute instrumented code on systems without
LTTng-UST installed.
To define LD_PRELOAD however affects too much. For instance all
forked processes also get the library loaded. This can be fixed by
removing the library from the LD_PRELOAD variable early in the main
function. This looks odd and required some explaining in comments.
Also, in my case, the instrumented program is started with a "wrapper"
program which I can not alter. This wrapper also gets the library
loaded.
As an alternative to using LD_PRELOAD I would like to use an explicit
function, like;
int traceload(char const* library_path);
that is called early in main (instead of the LD_PRELOAD environment
manipulation) and loads the library with dlopen if it exists.
I have already tried this (of course) and it almost works already.
The tracepoints becomes visible but I get no trace data written.
So I think a really small modification is needed.
Another alternative would be to implement an lttng-backend for latrace (
see: http://people.redhat.com/jolsa/latrace/index.shtml ).
Library calls from the following headers are supported as of version
0.5.11:
ctype.h dlfcn.h getopt.h ioctl.h libintl.h locale.h mman.h netdb.h
pwd.h signal.h stat.h stdlib.h sysdeps term.h time.h unistd.h
wait.h dirent.h fcntl.h inet.h latrace.h libio.h misc.h
ncurses.h pthread.h resource.h socket.h stdio.h string.h syslog.h termios.h
typedefs.h utmp.h
So if we let latrace optionally emit lttng events for call enter and exit we
would instantly get support for tracing for _any_ library call.
--
Paul
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