This is the mail archive of the systemtap@sourceware.org mailing list for the systemtap project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: failed to trace printf


Hi Mark, 

Thanks for quick and detailed reply.

> > 
> > # nm /lib64/libc.so.6 | grep -w -e __printf -e printf
> > 000000000004fdb0 t __printf
> > 000000000004fdb0 T printf
> > #
> > 
> > It fails for printf and works well for __printf. 
> > I actually expected it to be the other way.
> 
> So this just means that __printf has debuginfo associated with it and so
> we are able to find it. But printf doesn't (directly) have debuginfo
> associated with it, so we don't find it.

If we are unable to find debuginfo for a symbol, can we see if we have
alias functions like __printf in this case. (When I mean alias
functions, I refer to functions are having the same address). Can we use
the debuginfo of the alias function.  Here __printf and printf are
having same address 000000000004fdb0.  It may not be that easy. Probably
there are easier methods to do also.

> 
> > Also I tried with strcmp and that also failed.
> > # nm /lib64/libc.so.6 | grep strcmp
> > 0000003497880880 t __GI_strcmp
> > 0000003497880880 T strcmp
> > #
> > 
> > This time it failed for both _GI_strcmp and strcmp.
> 
> I haven't checked, but most likely strcmp is implemented through
> assembler as doesn't have dwarf information, or gcc uses an strcmp
> builtin function as optimization.
> 
 
I ran gdb on a program and it seems to refer gdb is able to refer to 
/usr/src/debug////////glibc-20081113T2206/string/../sysdeps/x86_64/strcmp.S
gdb is able to say when the breakpoint corresponding to strcmp is hit.
Though it was unable to give out variable info. Can we look at something
similar in stap? I mean we probe the function but say No local variable info
when ever we refer to variables.

--
Thanks and Regards
Srikar


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]