[lldb-dev] Extern globals showing up as locals

[Sam McCall via lldb-dev]

I'm seeing particular globals spuriously being reported as local variables:
they're returned by SBFrame::GetVariables(true, true, false, true) because
their scope is eValueTypeVariableLocal.

I've tracked down the problem but don't know DWARF well enough to determine
the right fix. Anyone want to help me out?

--

I can reproduce with the following program:

struct Obj{};
namespace N { extern Obj& o; }
using N::o;
int main(){}


When building with clang -g, lldb gives

(lldb) frame v -g -s

LOCAL: (Obj &) N::o = <no location, value may have been optimized out>

(lldb) target v -s

LOCAL: (Obj &) N::o = <no location, value may have been optimized out>

It seems confused about whether it's local or global.

readelf --dump-debug has the following info for the variable:
<2><31>: Abbrev Number: 3 (DW_TAG_variable)
    <32>   DW_AT_name        : (indirect string, offset: 0x51): o
    <36>   DW_AT_type        : <0x42>
    <3a>   DW_AT_external    : 1
    <3a>   DW_AT_decl_file   : 1
    <3b>   DW_AT_decl_line   : 2
    <3c>   DW_AT_declaration : 1
    <3c>   DW_AT_location    : 0 byte block:    ()
    <3d>   DW_AT_linkage_name: (indirect string, offset: 0x57): _ZN1N1oE
It seems that the zero-length location is a problem: SymbolFileDWARF.cpp
thinks a variable without a valid location must be static or local.

FWIW, gdb on the clang-built binary shows N::o as an optimized-out global,
which seems fine. gcc generates debug info that omits the DW_AT_location,
which causes gdb to hide it completely I think.

Cheers, Sam
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