RFC: stack trace generation

[Per Bothner]

Andrew Haley wrote:

> When you call a shared library, you jump via the PLT.  The PLT is a
> list of jump instructions that initially point to the dynamic loader
> but are replaced by direct jumps to library routines.  When you take
> the address of a routine, you get the address of a PLT entry, not the
> address of the routine itself.  This is true even if the routine you
> take the address of is in the same compliation unit.
> 
> Therefore, with current gcc semantics, it is impossible to get the
> true address of a routine that is declared to be global, and this
> causes great problems for the unwinder because the class metadata for
> methods points to PLT entries, not to the code for the methods.  So,
> when we have a code address on the stack we can't find out which
> method it is associated with.

Why can't you can have a target-dependent helper routine that can
extract the real function address from a PLT entry?  I realize there
is performance cost, but (for example) it should be possible to do
this mapping at class init time.
-- 
	--Per Bothner
per@bothner.com   http://per.bothner.com/