[Ltrace-devel] Support for systemtap probes in ltrace

[Petr Machata]

Hi there,

SDT probes are used by some application--typically, they are placed to
"strategic" places, such as when MySQL parses a query, or when OpenJDK
compiles a method.  I believe it would be useful for ltrace to be able
to put breakpoints on these.

I wrote a small patch that implements support for SDT probes to ltrace.
SDT probes are used by some applications.  This is how it looks when
used on a test binary of mine (edited to fit):

$ ./ltrace -x main ~/tmp/test
(0, 0, 561152, -1, 0x1f25bc2)                      = 0x33a9020260
__libc_start_main(0x400474, 1, 0x7fff451caf48 <unfinished ...>
main(1, 0x7fff451caf48, 0x7fff451caf58 <unfinished ...>
probe test::main()                                 = <void>
probe test::other()                                = <void>
<... main resumed> )                               = 0
+++ exited (status 0) +++

Probe arguments are not supported yet, and interpreting the GAS location
expressions, which the probe arguments use, might prove rather tricky
(and very arch-dependent).  So right now it's all presented as '()',
even though the "other" probe in my example actually has one argument.

It's on pmachata/stapsdt.  Comments welcome.

Thanks,
PM

P.S. if you want to learn more about the SDT probes:
http://sourceware.org/systemtap/wiki/AddingUserSpaceProbingToApps
http://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation