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[lldb] Backport D72880: "Fix a buffer-size bug when the first DW_OP_piece is undefined" #38

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[lldb] Backport D72880: "Fix a buffer-size bug when the first DW_OP_piece is undefined" #38

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6 changes: 5 additions & 1 deletion lldb/source/Expression/DWARFExpression.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2331,6 +2331,10 @@ bool DWARFExpression::Evaluate(
// not available. Fill with zeros for now by resizing the data and
// appending it
curr_piece.ResizeData(piece_byte_size);
// Note that "0" is not a correct value for the unknown bits.
// It would be better to also return a mask of valid bits together
// 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);
pieces.AppendDataToHostBuffer(curr_piece);
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This behavior of treating undef data as zeroed isn't ideal, but it should be fine for padding.

} else {
Expand Down Expand Up @@ -2445,8 +2449,8 @@ bool DWARFExpression::Evaluate(
return false;
}
}
op_piece_offset += piece_byte_size;
}
op_piece_offset += piece_byte_size;
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This is the fix, moving the offset update outside of the else arm of if (stack.empty()) {.

You can see the "then" arm above (handling undef pieces) because a comment was added to it.

}
} break;

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