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Re: [libunwind] Api to access local variable ?

From: David Mosberger
Subject: Re: [libunwind] Api to access local variable ?
Date: Fri, 6 Jun 2003 10:23:59 -0700

>>>>> On Fri, 06 Jun 2003 16:40:45 +0200 (CEST), David Jobet <address@hidden> 
>>>>> said:

  David.Jobet> I hope I'm not out of topic. If it is, just tell me : I
  David.Jobet> won't bother you anymore.

The question is perfectly on topic.

  David.Jobet> I'd like to know several things : 1 - do the unwind
  David.Jobet> table contains information about the local variables
  David.Jobet> defined in each functions (offset / frame pointer,
  David.Jobet> static type)

The unwind table(s) do _not_ contain such (debug) information.
Unwinding is quite a separate issue from debugging, though in the
past, the two were often mixed together.  But with languages that
require exception handling, you need unwind info even if you don't
need debug info (hence stripping a binary will remove the debug info,
but not the unwind info).

  David.Jobet> 2 - if yes, is there some functions in
  David.Jobet> libunwind's api to retrieve this information or is it
  David.Jobet> planned to develop these functions ? (couldn't find
  David.Jobet> them)


  David.Jobet> I've read gcc uses libunwind to do exception handling.
  David.Jobet> In C++, gcc have to call destructors of local variables
  David.Jobet> while unwinding stack.  I guessed (perhaps wrongly)
  David.Jobet> that there is information in the unwind table about
  David.Jobet> local variables of functions ?

No, the info about how to destroy a stack frame resides with the
compiler (and the code it generates), not the unwind library.  What
the unwind library does is call a "personality" routine which takes
care of all the language-specific handling.

  David.Jobet> The only information I cannot generate as static data
  David.Jobet> is the address of variables in the stack frame, so I'm
  David.Jobet> looking for a way to retrieve it using the unwind table
  David.Jobet> (of course, provided this information does exist !)

(I see Jim just answered this portion in a separate mail, so I'll skip
this one... ;-).


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