[Lldb-commits] [PATCH] D72880: Fix a buffer-size bug when the first DW_OP_piece is undefined

[Pavel Labath via Phabricator via lldb-commits]

labath added inline comments.


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Comment at: lldb/source/Expression/DWARFExpression.cpp:2077
+          // with the expression result, so the debugger can print missing
+          // members as "<optimized out>" or something.
           ::memset(curr_piece.GetBuffer().GetBytes(), 0, piece_byte_size);
----------------
vsk wrote:
> FTR I'm not really sure this case is allowed by the dwarf standard. Under DW_OP_piece the standard references a "preceding simple location description" -- istm like an error if the stack is empty. My $0.0002 :) 
I think this is fine -- an "empty location description" (section 2.6.1.1.4 of DWARF4) is a kind of a "simple location description" (sect. 2.6.1.1).

The part that worries me more is this: "Each simple location description that is a DWARF expression is evaluated independently of any others (as though on its own separate stack, if any).". I think that means we should reset/clear the stack after each DW_OP_piece, but we don't currently do that (we just pop the topmost value). However, I am not sure if this has any impact on valid DWARF expressions (though it can cause us to produce bogus values for invalid ones).


Repository:
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  https://reviews.llvm.org/D72880/new/

https://reviews.llvm.org/D72880