Julian Seward 9377cf0ea5 Add limited support for DWARF3 'expressions' in stack-unwind (CFI) ...

info (DW_CFA_def_cfa_expression, DW_CFA_expression,
DW_CFA_val_expression).  Mechanism to support all of these is in place
although only DW_CFA_val_expression is currently connected up.

This is really nasty.  The basic idea is to partially evaluate each
expression at the debuginfo-reading time by running it on a stack
machine in which each stack element is an expression tree.  If the
expression can be 'run' successfully, the tree (dag, really) remaining
at the top of the stack is massaged and put into the DiCfSI record for
that address range.  At unwind time the tree is evaluated if needed.
Such cases are in fact extremely rare and so the vast majority of
unwindings use the same mechanism as before.

As a result of all this:

* some obscure cases in glibc-2.5's libpthread.so unwind when they
  didn't before

* --debug-dump=frames produces identical output to that of readelf
  for libc-2.5.so and associated libpthread.so

* All the action centers around the new type CfiExpr, which is a
  union expression-tree type in the same style as IRExpr et al

* Many dark corners of the CFI reader have been looked at and
  (re-)validated



git-svn-id: svn://svn.valgrind.org/valgrind/trunk@6620

2007-02-27 16:52:23 +00:00

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