Hi,
I'm looking into something that seems like an inconsistency in handling of
the CIE pointer in FDEs in .debug_frame, between how debug info is
generated in LLVM and consumed in LLDB.
For FDEs in .eh_frame, the CIE pointer/cie_id field is interpreted as an
offset from the current FDE - this seems to be consistent.
But for cases in .debug_frame, they are treated differently. In LLDB, the
cie_id field is assumed to be relative to the begin of the .debug_frame
section:
https://github.com/llvm/llvm-project/blob/master/lldb/source/Symbol/DWARFCallFrameInfo.cpp#L482-L495
However, when this field is produced in LLVM, it can, depending on
MCAsmInfo flags, end up written as a plain absolute address to the CIE:
https://github.com/llvm/llvm-project/blob/master/llvm/lib/MC/MCDwarf.cpp#L1699-L1705
That code in MCDwarf.cpp hasn't been touched in many years, so I would
expect that the info it generates actually has been used since and been
found to be correct. Or are most cases built with -funwind-tables
or similar, enabled by default?, so this is exercised in untested cases?
In the case where I'm running in this, LLDB reports "error: Invalid cie
offset" when running executables with such .debug_frame sections.
By adding an ", true" to the end of the EmitSymbolValue call in
MCDwarf.cpp, the symbol reference is made section relative and the code
seems to do what LLDB expects. Is that correct, or should LLDB learn the
cases (which?) where the cie_id is an absolute address instead of a
section relative one?
// Martin
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