https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94469
Bug ID: 94469 Summary: lto abstract variable emitted as concrete decl (ada test-case) Product: gcc Version: 10.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: debug Assignee: unassigned at gcc dot gnu.org Reporter: vries at gcc dot gnu.org Target Milestone: --- Consider gdb testsuite test-case gdb.ada/call_pn ( https://sourceware.org/git/?p=binutils-gdb.git;a=tree;f=gdb/testsuite/gdb.ada/call_pn;hb=HEAD ), consisting of files foo.adb, pck.adb and pck.ads. Compiled like so: ... $ gnatmake-10 \ --GCC=/usr/bin/gcc-10 \ --GNATBIND=/usr/bin/gnatbind-10 \ --GNATLINK=/usr/bin/gnatlink-10 \ -largs --GCC=/usr/bin/gcc-10 -margs \ src/gdb/testsuite/gdb.ada/call_pn/foo.adb \ -g -flto -O0 -flto-partition=none -ffat-lto-objects ... When trying to print the value of last_node_id, we get a question which symbol to print: ... $ gdb foo -ex "p last_node_id" Reading symbols from foo... Multiple matches for last_node_id [0] cancel [1] pck.last_node_id at src/gdb/testsuite/gdb.ada/call_pn/pck.adb:17 [2] pck.last_node_id at src/gdb/testsuite/gdb.ada/call_pn/foo.adb:17 > ... where 1 gives us: ... > 1 $1 = <optimized out> ... and 2 gives us: ... > 2 $1 = 0 ... If we compile without lto, so just with -g, we have instead: ... $ gdb foo -ex "p last_node_id" $1 = 0 ... The structure of the dwarf for the lto case is: ... <0><15ef>: Abbrev Number: 1 (DW_TAG_compile_unit) <15f5> DW_AT_name : <artificial> <1><1611>: Abbrev Number: 2 (DW_TAG_imported_unit) <1612> DW_AT_import : <0x167a> [Abbrev Number: 1] <1><163f>: Abbrev Number: 5 (DW_TAG_variable) <1640> DW_AT_abstract_origin: <0x16d4> <1644> DW_AT_location : 9 byte block: 3 d4 33 63 0 0 0 0 0 (DW_OP_addr: 6333d4) <0><167a>: Abbrev Number: 1 (DW_TAG_compile_unit) <1680> DW_AT_name : src/gdb/testsuite/gdb.ada/call_pn/pck.adb <1><16d4>: Abbrev Number: 8 (DW_TAG_variable) <16d5> DW_AT_name : pck__last_node_id ... My understanding of DWARF is that this actually declares three symbols: - the one for DW_TAG_compile_unit pck.adb - the one for DW_TAG_compile_unit <artificial> - the one resulting from the import of <pck.adb> into DW_TAG_compile_unit <artificial> And, AFAIU, the way to make sure we declare just one symbol is by both: - dropping the import, and - changing the tag for pck.adb to DW_TAG_partial_unit. The import was already dropped on master by commit 54af95767e8 "debug/94450 - remove DW_TAG_imported_unit generated in LTRANS units" ( see PR 94450 comment 6 ). Note: interestingly, the foo.adb here is incorrect: ... [1] pck.last_node_id at src/gdb/testsuite/gdb.ada/call_pn/pck.adb:17 [2] pck.last_node_id at src/gdb/testsuite/gdb.ada/call_pn/foo.adb:17 ... For now I'm assuming that's a gdb PR, filed as PR gdb/25771 - "Inter-cu DW_AT_abstract_origin results in wrong file".