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[ELF] Improve undefined symbol message w/ DW_TAG_variable of the enclosing symbol but w/o line number information (#70854)
The undefined symbol message suggests the source line when line number information is available (see https://reviews.llvm.org/D31481). When the undefined symbol is from a global variable, we won't get the line information. ``` extern int undef; namespace ns { int *var[] = { &undef }; // DW_TAG_variable(DW_AT_decl_file/DW_AT_decl_line) is available while // line number information is unavailable. } ld.lld: error: undefined symbol: undef >>> referenced by undef-debug2.cc >>> undef-debug2.o:(ns::var) ``` This patch utilizes `getEnclosingSymbol` to locate `var` and find DW_TAG_variable for `var`: ``` ld.lld: error: undefined symbol: undef >>> referenced by undef-debug2.cc:3 (/tmp/c/undef-debug2.cc:3) >>> undef-debug2.o:(ns::var) ```
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‎lld/ELF/Relocations.cpp

Lines changed: 4 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -739,7 +739,10 @@ static void reportUndefinedSymbol(const UndefinedDiag &undef,
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uint64_t offset = l.offset;
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msg += "\n>>> referenced by ";
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std::string src = sec.getSrcMsg(sym, offset);
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// In the absence of line number information, utilize DW_TAG_variable (if
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// present) for the enclosing symbol (e.g. var in `int *a[] = {&undef};`).
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Symbol *enclosing = sec.getEnclosingSymbol(offset);
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std::string src = sec.getSrcMsg(enclosing ? *enclosing : sym, offset);
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if (!src.empty())
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msg += src + "\n>>> ";
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msg += sec.getObjMsg(offset);

‎lld/test/ELF/Inputs/undef-debug.s

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1,3 +1,4 @@
1+
## Variables with line number information
12
.file 1 "dir/undef-debug.s"
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.loc 1 3
34
.quad zed3

‎lld/test/ELF/Inputs/undef-debug2.s

Lines changed: 200 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,200 @@
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## Generate from:
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##
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## extern int zed9;
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## namespace ns {
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## int *var[] = {
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## &zed9
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## };
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## }
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.text
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.file "undef-debug2.cc"
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.file 0 "dir" "undef-debug2.cc" md5 0xd7caefb836c47f6c56303f19e96f2587
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.type _ZN2ns3varE,@object # @_ZN2ns3varE
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.data
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.globl _ZN2ns3varE
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.p2align 3, 0x0
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_ZN2ns3varE:
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.quad zed9
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.size _ZN2ns3varE, 8
19+
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.section .debug_abbrev,"",@progbits
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.byte 1 # Abbreviation Code
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.byte 17 # DW_TAG_compile_unit
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.byte 1 # DW_CHILDREN_yes
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.byte 37 # DW_AT_producer
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.byte 37 # DW_FORM_strx1
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.byte 19 # DW_AT_language
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.byte 5 # DW_FORM_data2
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.byte 3 # DW_AT_name
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.byte 37 # DW_FORM_strx1
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.byte 114 # DW_AT_str_offsets_base
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.byte 23 # DW_FORM_sec_offset
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.byte 16 # DW_AT_stmt_list
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.byte 23 # DW_FORM_sec_offset
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.byte 27 # DW_AT_comp_dir
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.byte 37 # DW_FORM_strx1
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.byte 115 # DW_AT_addr_base
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.byte 23 # DW_FORM_sec_offset
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.byte 0 # EOM(1)
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.byte 0 # EOM(2)
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.byte 2 # Abbreviation Code
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.byte 57 # DW_TAG_namespace
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.byte 1 # DW_CHILDREN_yes
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.byte 3 # DW_AT_name
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.byte 37 # DW_FORM_strx1
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.byte 0 # EOM(1)
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.byte 0 # EOM(2)
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.byte 3 # Abbreviation Code
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.byte 52 # DW_TAG_variable
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.byte 0 # DW_CHILDREN_no
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.byte 3 # DW_AT_name
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.byte 37 # DW_FORM_strx1
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.byte 73 # DW_AT_type
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.byte 19 # DW_FORM_ref4
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.byte 63 # DW_AT_external
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.byte 25 # DW_FORM_flag_present
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.byte 58 # DW_AT_decl_file
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.byte 11 # DW_FORM_data1
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.byte 59 # DW_AT_decl_line
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.byte 11 # DW_FORM_data1
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.byte 2 # DW_AT_location
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.byte 24 # DW_FORM_exprloc
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.byte 110 # DW_AT_linkage_name
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.byte 37 # DW_FORM_strx1
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.byte 0 # EOM(1)
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.byte 0 # EOM(2)
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.byte 4 # Abbreviation Code
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.byte 1 # DW_TAG_array_type
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.byte 1 # DW_CHILDREN_yes
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.byte 73 # DW_AT_type
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.byte 19 # DW_FORM_ref4
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.byte 0 # EOM(1)
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.byte 0 # EOM(2)
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.byte 5 # Abbreviation Code
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.byte 33 # DW_TAG_subrange_type
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.byte 0 # DW_CHILDREN_no
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.byte 73 # DW_AT_type
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.byte 19 # DW_FORM_ref4
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.byte 55 # DW_AT_count
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.byte 11 # DW_FORM_data1
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.byte 0 # EOM(1)
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.byte 0 # EOM(2)
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.byte 6 # Abbreviation Code
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.byte 15 # DW_TAG_pointer_type
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.byte 0 # DW_CHILDREN_no
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.byte 73 # DW_AT_type
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.byte 19 # DW_FORM_ref4
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.byte 0 # EOM(1)
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.byte 0 # EOM(2)
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.byte 7 # Abbreviation Code
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.byte 36 # DW_TAG_base_type
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.byte 0 # DW_CHILDREN_no
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.byte 3 # DW_AT_name
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.byte 37 # DW_FORM_strx1
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.byte 62 # DW_AT_encoding
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.byte 11 # DW_FORM_data1
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.byte 11 # DW_AT_byte_size
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.byte 11 # DW_FORM_data1
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.byte 0 # EOM(1)
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.byte 0 # EOM(2)
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.byte 8 # Abbreviation Code
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.byte 36 # DW_TAG_base_type
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.byte 0 # DW_CHILDREN_no
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.byte 3 # DW_AT_name
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.byte 37 # DW_FORM_strx1
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.byte 11 # DW_AT_byte_size
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.byte 11 # DW_FORM_data1
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.byte 62 # DW_AT_encoding
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.byte 11 # DW_FORM_data1
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.byte 0 # EOM(1)
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.byte 0 # EOM(2)
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.byte 0 # EOM(3)
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.section .debug_info,"",@progbits
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.Lcu_begin0:
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.long .Ldebug_info_end0-.Ldebug_info_start0 # Length of Unit
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.Ldebug_info_start0:
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.short 5 # DWARF version number
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.byte 1 # DWARF Unit Type
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.byte 8 # Address Size (in bytes)
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.long .debug_abbrev # Offset Into Abbrev. Section
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.byte 1 # Abbrev [1] 0xc:0x3b DW_TAG_compile_unit
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.byte 0 # DW_AT_producer
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.short 33 # DW_AT_language
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.byte 1 # DW_AT_name
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.long .Lstr_offsets_base0 # DW_AT_str_offsets_base
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.long .Lline_table_start0 # DW_AT_stmt_list
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.byte 2 # DW_AT_comp_dir
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.long .Laddr_table_base0 # DW_AT_addr_base
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.byte 2 # Abbrev [2] 0x1e:0xf DW_TAG_namespace
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.byte 3 # DW_AT_name
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.byte 3 # Abbrev [3] 0x20:0xc DW_TAG_variable
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.byte 4 # DW_AT_name
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.long 45 # DW_AT_type
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# DW_AT_external
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.byte 0 # DW_AT_decl_file
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.byte 3 # DW_AT_decl_line
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.byte 2 # DW_AT_location
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.byte 161
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.byte 0
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.byte 7 # DW_AT_linkage_name
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.byte 0 # End Of Children Mark
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.byte 4 # Abbrev [4] 0x2d:0xc DW_TAG_array_type
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.long 57 # DW_AT_type
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.byte 5 # Abbrev [5] 0x32:0x6 DW_TAG_subrange_type
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.long 66 # DW_AT_type
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.byte 1 # DW_AT_count
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.byte 0 # End Of Children Mark
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.byte 6 # Abbrev [6] 0x39:0x5 DW_TAG_pointer_type
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.long 62 # DW_AT_type
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.byte 7 # Abbrev [7] 0x3e:0x4 DW_TAG_base_type
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.byte 5 # DW_AT_name
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.byte 5 # DW_AT_encoding
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.byte 4 # DW_AT_byte_size
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.byte 8 # Abbrev [8] 0x42:0x4 DW_TAG_base_type
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.byte 6 # DW_AT_name
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.byte 8 # DW_AT_byte_size
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.byte 7 # DW_AT_encoding
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.byte 0 # End Of Children Mark
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.Ldebug_info_end0:
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.section .debug_str_offsets,"",@progbits
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.long 36 # Length of String Offsets Set
161+
.short 5
162+
.short 0
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.Lstr_offsets_base0:
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.section .debug_str,"MS",@progbits,1
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.Linfo_string0:
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.asciz "clang version 18.0.0" # string offset=0
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.Linfo_string1:
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.asciz "undef-debug2.cc" # string offset=21
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.Linfo_string2:
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.asciz "dir" # string offset=37
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.Linfo_string3:
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.asciz "ns" # string offset=44
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.Linfo_string4:
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.asciz "var" # string offset=47
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.Linfo_string5:
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.asciz "int" # string offset=51
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.Linfo_string6:
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.asciz "__ARRAY_SIZE_TYPE__" # string offset=55
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.Linfo_string7:
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.asciz "_ZN2ns3varE" # string offset=75
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.section .debug_str_offsets,"",@progbits
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.long .Linfo_string0
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.long .Linfo_string1
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.long .Linfo_string2
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.long .Linfo_string3
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.long .Linfo_string4
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.long .Linfo_string5
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.long .Linfo_string6
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.long .Linfo_string7
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.section .debug_addr,"",@progbits
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.long .Ldebug_addr_end0-.Ldebug_addr_start0 # Length of contribution
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.Ldebug_addr_start0:
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.short 5 # DWARF version number
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.byte 8 # Address size
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.byte 0 # Segment selector size
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.Laddr_table_base0:
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.quad _ZN2ns3varE
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.Ldebug_addr_end0:
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.section .debug_line,"",@progbits
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.Lline_table_start0:

‎lld/test/ELF/undef.s

Lines changed: 7 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -3,11 +3,12 @@
33
# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %p/Inputs/undef.s -o %t2.o
44
# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %p/Inputs/undef-debug.s -o %t3.o
55
# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %p/Inputs/undef-bad-debug.s -o %t4.o
6+
# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %p/Inputs/undef-debug2.s -o %t5.o
67
# RUN: rm -f %t2.a
78
# RUN: llvm-ar rc %t2.a %t2.o
8-
# RUN: not ld.lld --threads=1 %t.o %t2.a %t3.o %t4.o -o /dev/null 2>&1 \
9+
# RUN: not ld.lld --threads=1 %t.o %t2.a %t3.o %t4.o %t5.o -o /dev/null 2>&1 \
910
# RUN: | FileCheck %s --implicit-check-not="error:" --implicit-check-not="warning:"
10-
# RUN: not ld.lld --threads=1 -pie %t.o %t2.a %t3.o %t4.o -o /dev/null 2>&1 \
11+
# RUN: not ld.lld --threads=1 -pie %t.o %t2.a %t3.o %t4.o %t5.o -o /dev/null 2>&1 \
1112
# RUN: | FileCheck %s --implicit-check-not="error:" --implicit-check-not="warning:"
1213

1314
# CHECK: error: undefined symbol: foo
@@ -82,6 +83,10 @@
8283
# CHECK-NEXT: >>> referenced by undef-bad-debug2.s:11 (dir2{{/|\\}}undef-bad-debug2.s:11)
8384
# CHECK-NEXT: >>> {{.*}}tmp4.o:(.text+0x18)
8485

86+
# CHECK: error: undefined symbol: zed9
87+
# CHECK-NEXT: >>> referenced by undef-debug2.cc:3 (dir{{/|\\}}undef-debug2.cc:3)
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# CHECK-NEXT: >>> {{.*}}tmp5.o:(ns::var)
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8590
# RUN: not ld.lld %t.o %t2.a -o /dev/null -no-demangle 2>&1 | \
8691
# RUN: FileCheck -check-prefix=NO-DEMANGLE %s
8792
# NO-DEMANGLE: error: undefined symbol: _Z3fooi

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