problem in User-Space Probing

problem in User-Space Probing

[ch huang]

i write a test function ,

#include <stdio.h>

static void my_out(void)
{
        printf("just a test\n");
}
main()
{
        printf("befor function\n");
        my_out();
        printf("after function\n");
}

and compile it
gcc -g -gdwarf-2 -g3  test.c  -o test

then write stap script

probe process("/root/test").function("my_out"){
printf("i in %s\n",pp())
}
probe process("/root/test").function("my_out").return{
printf("back from %s\n",probefunc())
}
when i run this script i find some warning information

# stap exec.stp
/usr/local/share/systemtap/runtime/uprobes/uprobes.c: In function
‘uprobe_report_exec’:
/usr/local/share/systemtap/runtime/uprobes/uprobes.c:2401: warning:
‘uproc’ may be used uninitialized in this function
/usr/local/share/systemtap/runtime/uprobes/uprobes.c: In function
‘uprobe_report_exit’:
/usr/local/share/systemtap/runtime/uprobes/uprobes.c:2101: warning:
‘uproc’ may be used uninitialized in this function
i in process("/root/test").function("my_out@/root/test.c:4")
back from my_out

it seems script works fine ,but i do not know the warning info,is
there something i missed?

Re: problem in User-Space Probing

[Srikar Dronamraju]

> 
> probe process("/root/test").function("my_out"){
> printf("i in %s\n",pp())
> }
> probe process("/root/test").function("my_out").return{
> printf("back from %s\n",probefunc())
> }
> when i run this script i find some warning information
> 
> # stap exec.stp
> /usr/local/share/systemtap/runtime/uprobes/uprobes.c: In function
> ?uprobe_report_exec?:
> /usr/local/share/systemtap/runtime/uprobes/uprobes.c:2401: warning:
> ?uproc? may be used uninitialized in this function
> /usr/local/share/systemtap/runtime/uprobes/uprobes.c: In function
> ?uprobe_report_exit?:
> /usr/local/share/systemtap/runtime/uprobes/uprobes.c:2101: warning:
> ?uproc? may be used uninitialized in this function
> i in process("/root/test").function("my_out@/root/test.c:4")
> back from my_out
> 
> it seems script works fine ,but i do not know the warning info,is
> there something i missed?
> 

It would have been good if you had given your stap setup details.
I think you are running on a kernel < 2.6.24.

From the code walk through, I dont see a case for uproc being not
initialized.  I think its a compiler bug. 

https://lkml.org/lkml/2011/11/28/287

-- 
Thanks and Regards
Srikar

Re: problem in User-Space Probing

[Frank Ch. Eigler]

ch huang <justlooks@gmail.com> writes:

> [...]
> /usr/local/share/systemtap/runtime/uprobes/uprobes.c: In function
> 'uprobe_report_exec':
> /usr/local/share/systemtap/runtime/uprobes/uprobes.c:2401: warning:
> 'uproc' may be used uninitialized in this function
> /usr/local/share/systemtap/runtime/uprobes/uprobes.c: In function
> 'uprobe_report_exit':
> /usr/local/share/systemtap/runtime/uprobes/uprobes.c:2101: warning:
> 'uproc' may be used uninitialized in this function
> i in process("/root/test").function("my_out@/root/test.c:4")

It sounds like some overpicky compiler.  Please try adding a

    = NULL;

to those declarations on those source files.  If it works for you,
please send us that diff/patch to apply to the source tree.


- FChE