Re: Stabs or Dwarf Was: [PATCH]: testsuite/gdb.base/constvars.exp

[Elena Zannoni <ezannoni at cygnus dot com>]

Fernando Nasser writes:
 > Elena Zannoni wrote:
 > > 
 > > Fernando Nasser writes:
 > >  > Hi Stan,
 > >  >
 > >  > Thanks for your comments.
 > >  >
 > >  > Stan Shebs wrote:
 > >  > >
 > >  > > I can't think of a completely reliable test on binary files.  For
 > >  > > instance, in original a.out, stabs are plain symbols, not in a
 > >  > > distinctly-named section.  You also have the problem of an executable
 > >  > > maybe having libraries compiled with stabs, and main prog with dwarf,
 > >  > > and objdump can't distinguish.
 > >  > >
 > >  >
 > >  > True.
 > >  >
 > >  > I was thinking just in terms of the testsuite.  Most test programs are
 > >  > a single file.  Could we test just the object file for that one?
 > > 
 > > I have seen cases in which we have both a .mdebug and a .stabs (or was
 > > that dwarf2) sections (for the same program segment), and even gdb
 > > itself gets confused as to which one is the reliable debug
 > > info. Frankly I wouldn't be able to say exactly under which
 > > circumstances you get this, but I have seen it.
 > > 
 > > I think this is basically what Stan is saying, the heuristic is
 > > unreliable.
 > > 
 > 
 > When you mean that gdb itself gets confused what is the end result of
 > that?
 > Does it pick one at the end (after a warning or something)?

No warning. For instance I have seen it pick the mdebug info which is
incomplete/incorrect. I have looked back at some old mail, and it was
with mdebug and dwarf2. I'll see if I can figure out what was
happening.

 > 
 > Another question: does it happen even with the simple testsuite
 > programs?
 > 

Don't know. I would think so. If the compiler emits 2 types of debug
info, it, in theory, should behave the same with any program.

 > If it is that unreliable, we could make sure the tests run with dwarf
 > only
 > when we are sure it is there and skip when we are not sure (if we can
 > determine that we are not sure from some gdb warning message).
 > 

It would be probably reliable 'in general'. Probably not that many
platforms emit both mdebug & dwarf2.

 > P.S.: We can also be more aggressive and try and see where gdb gets
 > confused
 > and thinks it is dwarf (and so fail the tests).  We could dig for the
 > reason
 > that happens.  Just a thought. 
 > 
 > 

Yep.

Elena

 > -- 
 > Fernando Nasser
 > Red Hat Canada Ltd.                     E-Mail:  fnasser@redhat.com
 > 2323 Yonge Street, Suite #300
 > Toronto, Ontario   M4P 2C9