On 8/24/21 12:55 AM, Richard Biener wrote:
On Mon, Aug 23, 2021 at 11:18 PM Indu Bhagat via Gcc-patches <gcc-patches@gcc.gnu.org> wrote: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 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>I suppose having both a DW_AT_specification and a DW_AT_type is somewhat at odds. It's likely because the definition specifies the size of the array while the specification does not. Not sure what should be best done here. Richard.
Hmm..I thought the generated DWARF by gcc-trunk for testcase 2 is coherent and specifies the information in alignment with the source : DW_AT_type of the defining declaration correctly specifies the type to be const char[7] while the DW_AT_specification pointing to the non-defining decl (and with type const char[] with no size info).
The DWARF generated by gcc-8.4.1, however, does seem to be missing information though. It should have the information for the defining decl and hence, the size info. i.e., DW_AT_type pointing to a array with DW_TAG_subrange_type with attribute DW_AT_upper_bound = 6 like above. Isn't it ?
Indu
<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
