[Bug runtime/10857] New: dwarf unwinder doesn't handle call frame instructions taking expressions

[Bug runtime/10857] New: dwarf unwinder doesn't handle call frame instructions taking expressions

[mjw at redhat dot com]

The runtime dwarf unwinder doesn't handle DW_CFA_def_cfa_expression,
DW_CFA_expression and DW_CFA_val_expression which handle values defined as dwarf
operations. The unwinder fails in such cases and we need to fall back to raw
stack walking.

It would be nice to reuse some of the loc2c code for this so we are able to kind
of precompile the operations. That would also benefit from the (stack depth)
limits already in place in loc2c (but note that not all dwarf expressions are
allowed in the call frame information). It isn't clear how to do this simply.

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           Summary: dwarf unwinder doesn't handle call frame instructions
                    taking expressions
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: runtime
        AssignedTo: systemtap at sources dot redhat dot com
        ReportedBy: mjw at redhat dot com


http://sourceware.org/bugzilla/show_bug.cgi?id=10857

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[Bug runtime/10857] dwarf unwinder doesn't handle call frame instructions taking expressions

[fche at redhat dot com]

------- Additional Comments From fche at redhat dot com  2010-05-06 13:17 -------
Have such expressions been seen in the wild?

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[Bug runtime/10857] dwarf unwinder doesn't handle call frame instructions taking expressions

[roland at gnu dot org]

------- Additional Comments From roland at gnu dot org  2010-05-07 01:32 -------
If "in the wild" means do they actually appear in real binaries, the answer is
yes.  If you mean "has it hampered some unwinding some systemtap user tried",
then who knows.

pmachata recently did some scripted CFI analysis on a large raft of OS binaries,
which cited the subset of these cases where a recently-fixed gcc bug was
involved.  It would be simpler to script grepping for all DW_CFA_expression,
DW_CFA_def_cfa_expression, and DW_CFA_val_expression uses.

GCC can emit DW_CFA_expression and DW_CFA_def_cfa_expression for x86 and perhaps
other machines.  Without doing the aforementioned grepping, off hand we have
only noticed it being used in x86-32 code generation so far.

glibc uses those in the signal frame on x86_64, and uses DW_CFA_val_expression
in its locking code (used both inside glibc and for libpthread) for x86_64 and i386.

-- 


http://sourceware.org/bugzilla/show_bug.cgi?id=10857

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[Bug runtime/10857] dwarf unwinder doesn't handle call frame instructions taking expressions

[roland at gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
OtherBugsDependingO|                            |11898
              nThis|                            |


http://sourceware.org/bugzilla/show_bug.cgi?id=10857

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[Bug runtime/10857] dwarf unwinder doesn't handle call frame instructions taking expressions

[fche at redhat dot com]

------- Additional Comments From fche at redhat dot com  2010-08-16 18:28 -------
*** Bug 11898 has been marked as a duplicate of this bug. ***

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