Hello,
What is the expected DWARF for extern variable in the following cases? I
am seeing that the DWARF generated is different with gcc8.4.1 vs gcc-trunk.
Testcase 1
----------
extern const char a[];
int foo()
{
return a != 0;
}
Testcase 1 Behavior
---------------------
- gcc-trunk has _no_ DWARF for variable a.
- gcc8.4.1 generates following DW_TAG_variable for extern variable a.
But does not designate it as a non-defining decl (IIUC,
DW_AT_specification is used for such cases?).
<..>
<1><31>: Abbrev Number: 2 (DW_TAG_array_type)
<32> DW_AT_type : <0x48>
<36> DW_AT_sibling : <0x3c>
<2><3a>: Abbrev Number: 3 (DW_TAG_subrange_type)
<2><3b>: Abbrev Number: 0
<1><3c>: Abbrev Number: 4 (DW_TAG_const_type)
<3d> DW_AT_type : <0x31>
<1><41>: Abbrev Number: 5 (DW_TAG_base_type)
<42> DW_AT_byte_size : 1
<43> DW_AT_encoding : 6 (signed char)
<44> DW_AT_name : (indirect string, offset: 0x1df6): char
<1><48>: Abbrev Number: 4 (DW_TAG_const_type)
<49> DW_AT_type : <0x41>
<1><4d>: Abbrev Number: 6 (DW_TAG_variable)
<4e> DW_AT_name : a
<50> DW_AT_decl_file : 1
<51> DW_AT_decl_line : 1
<52> DW_AT_decl_column : 19
<53> DW_AT_type : <0x3c>
<57> DW_AT_external : 1
<57> DW_AT_declaration : 1
<..>
-----------------------------------------------------------
Testcase 2
----------
extern const char a[];
const char a[] = "testme";
Testcase 2 Behavior
--------------------
- Both gcc-trunk and gcc8.4.1 generate two DW_TAG_variable DIEs (the
defining decl holds the reference to the non-defining decl via
DW_AT_specification)
- But gcc8.4.1 does not generate any DWARF for the type of the defining
decl (const char[7]) but gcc-trunk does.
## DWARF for testcase 2 with gcc-trunk is as follows:
<...>
<1><22>: Abbrev Number: 2 (DW_TAG_array_type)
<23> DW_AT_type : <0x39>
<27> DW_AT_sibling : <0x2d>
<2><2b>: Abbrev Number: 5 (DW_TAG_subrange_type)
<2><2c>: Abbrev Number: 0
<1><2d>: Abbrev Number: 1 (DW_TAG_const_type)
<2e> DW_AT_type : <0x22>
<1><32>: Abbrev Number: 3 (DW_TAG_base_type)
<33> DW_AT_byte_size : 1
<34> DW_AT_encoding : 6 (signed char)
<35> DW_AT_name : (indirect string, offset: 0x2035): char
<1><39>: Abbrev Number: 1 (DW_TAG_const_type)
<3a> DW_AT_type : <0x32>
<1><3e>: Abbrev Number: 6 (DW_TAG_variable)
<3f> DW_AT_name : a
<41> DW_AT_decl_file : 1
<42> DW_AT_decl_line : 1
<43> DW_AT_decl_column : 19
<44> DW_AT_type : <0x2d>
<48> DW_AT_external : 1
<48> DW_AT_declaration : 1
<1><48>: Abbrev Number: 2 (DW_TAG_array_type)
<49> DW_AT_type : <0x39>
<4d> DW_AT_sibling : <0x58>
<2><51>: Abbrev Number: 7 (DW_TAG_subrange_type)
<52> DW_AT_type : <0x5d>
<56> DW_AT_upper_bound : 6
<2><57>: Abbrev Number: 0
<1><58>: Abbrev Number: 1 (DW_TAG_const_type)
<59> DW_AT_type : <0x48>
<1><5d>: Abbrev Number: 3 (DW_TAG_base_type)
<5e> DW_AT_byte_size : 8
<5f> DW_AT_encoding : 7 (unsigned)
<60> DW_AT_name : (indirect string, offset: 0x2023): long
unsigned int
<1><64>: Abbrev Number: 8 (DW_TAG_variable)
<65> DW_AT_specification: <0x3e>
<69> DW_AT_decl_line : 2
<6a> DW_AT_decl_column : 12
<6b> DW_AT_type : <0x58>
<6f> DW_AT_location : 9 byte block: 3 0 0 0 0 0 0 0 0
(DW_OP_addr: 0)
<1><79>: Abbrev Number: 0
## DWARF for testcase 2 with gcc8.4.1 is as follows:
<1><21>: Abbrev Number: 2 (DW_TAG_array_type)
<22> DW_AT_type : <0x38>
<26> DW_AT_sibling : <0x2c>
<2><2a>: Abbrev Number: 3 (DW_TAG_subrange_type)
<2><2b>: Abbrev Number: 0
<1><2c>: Abbrev Number: 4 (DW_TAG_const_type)
<2d> DW_AT_type : <0x21>
<1><31>: Abbrev Number: 5 (DW_TAG_base_type)
<32> DW_AT_byte_size : 1
<33> DW_AT_encoding : 6 (signed char)
<34> DW_AT_name : (indirect string, offset: 0x1e04): char
<1><38>: Abbrev Number: 4 (DW_TAG_const_type)
<39> DW_AT_type : <0x31>
<1><3d>: Abbrev Number: 6 (DW_TAG_variable)
<3e> DW_AT_name : a
<40> DW_AT_decl_file : 1
<41> DW_AT_decl_line : 1
<42> DW_AT_decl_column : 19
<43> DW_AT_type : <0x2c>
<47> DW_AT_external : 1
<47> DW_AT_declaration : 1
<1><47>: Abbrev Number: 5 (DW_TAG_base_type)
<48> DW_AT_byte_size : 8
<49> DW_AT_encoding : 7 (unsigned)
<4a> DW_AT_name : (indirect string, offset: 0x1df2): long
unsigned int
<1><4e>: Abbrev Number: 7 (DW_TAG_variable)
<4f> DW_AT_specification: <0x3d>
<53> DW_AT_decl_line : 2
<54> DW_AT_decl_column : 12
<55> DW_AT_location : 9 byte block: 3 0 0 0 0 0 0 0 0
(DW_OP_addr: 0)
<1><5f>: Abbrev Number: 0
Thanks
Indu
