[Bug gas/29451] gas-2.39 started adding 0-sized DIEs to functions without .size

[mliska at suse dot cz]

https://sourceware.org/bugzilla/show_bug.cgi?id=29451

--- Comment #6 from Martin Liska <mliska at suse dot cz> ---
(In reply to Mark Wielaard from comment #5)
> >> So when this file is linked in with object files and these relocations are
> >> resolved the correct values for the __x86.get_pc_thunk.bx symbol will be
> >> installed into the .debug_info section, and everything should work.
> >
> > In https://sourceware.org/PR29450 we observed zero-size on a final 
> > executable.
> 
> Maybe it is useful to attach the final binary to this bug and show how to
> generate it.
> 
> Given the code that introduced this issues (commit
> 591cc9fbbfd6d51131c0f1d4a92e7893edcc7a28 see comment #1) it might also be
> interesting to show the symbol table entry for _init.

Note before the revision there was no debug info entry for _init:

$ as --version && gcc /tmp/crti.S -c -g --verbose -dwarf4 && readelf
--debug-dump crti.o
GNU assembler (GNU Binutils; openSUSE Tumbleweed) 2.38.20220525-6
...
 <0><c>: Abbrev Number: 1 (DW_TAG_compile_unit)
    <d>   DW_AT_stmt_list   : 0x0
    <11>   DW_AT_ranges      : 0xc
    <15>   DW_AT_name        : (indirect string, offset: 0x0): /tmp/crti.S
    <19>   DW_AT_comp_dir    : (indirect string, offset: 0xc): /home/marxin
    <1d>   DW_AT_producer    : (indirect string, offset: 0x19): GNU AS 2.38
    <21>   DW_AT_language    : 32769    (MIPS assembler)

(no change with -dwarf4 option). And the symbol has size == 0 in symbol table:
$ readelf -s crti.o

Symbol table '.symtab' contains 11 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
...
     9: 0000000000000000     0 FUNC    GLOBAL HIDDEN     5 _init

With 2.39 one gets:
$ as --version && gcc /tmp/crti.S -c -g --verbose -dwarf4 && readelf
--debug-dump crti.o
GNU assembler (GNU Binutils; home:marxin:branches:devel:gcc / openSUSE_Factory)
2.39.0.20220808-0
...
 <0><c>: Abbrev Number: 1 (DW_TAG_compile_unit)
    <d>   DW_AT_stmt_list   : 0x0
    <11>   DW_AT_ranges      : 0xc
    <15>   DW_AT_name        : (indirect string, offset: 0x0): /tmp/crti.S
    <19>   DW_AT_comp_dir    : (indirect string, offset: 0xc):
/home/marxin/Programming/binutils
    <1d>   DW_AT_producer    : (indirect string, offset: 0x2e): GNU AS 2.39.0
    <21>   DW_AT_language    : 32769    (MIPS assembler)
 <1><23>: Abbrev Number: 2 (DW_TAG_subprogram)
    <24>   DW_AT_name        : (indirect string, offset: 0x3c): _init
    <28>   DW_AT_external    : 1
    <28>   DW_AT_low_pc      : 0x0
    <30>   DW_AT_high_pc     : 0
 <1><31>: Abbrev Number: 2 (DW_TAG_subprogram)
    <32>   DW_AT_name        : (indirect string, offset: 0x42):
__x86.get_pc_thunk.bx
    <36>   DW_AT_external    : 1
    <36>   DW_AT_low_pc      : 0x0
    <3e>   DW_AT_high_pc     : 2
 <1><3f>: Abbrev Number: 0

and the symbol size is also 0 in the table:
$ readelf -s crti.o

Symbol table '.symtab' contains 11 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
...
     9: 0000000000000000     0 FUNC    GLOBAL HIDDEN     5 _init

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