[Dwarf-Discuss] Alternate entry points

[Jakub Jelinek]

On Wed, Oct 24, 2018 at 01:00:26AM -0400, Rafik Zurob via Dwarf-Discuss wrote:
> > I dug up gfortran 5.4, which does not emit DW_TAG_entry_point with my
> > simple example program.  Does anybody actually use it?
> 
> IBM XL Fortran generates it.
> 
> $ cat entry.f
> subroutine foo(a)
>   integer a
>   real b
> 
>   a = 5
>   return
> entry bar(b)
>   b = 3.0
>   return
> end subroutine
> $
> 
> Gets the following DWARF:

That is kind of weird, because foo only has dummy argument a
and entry bar only has b, there is nothing that tells the debug info
consumer that the subprogram doesn't have (a, b) arguments.

>  <1><42>: Abbrev Number: 2 (DW_TAG_base_type)
>     <43>   DW_AT_name        : INTEGER
>     <4b>   DW_AT_byte_size   : 4
>     <4c>   DW_AT_encoding    : 5        (signed)
>  <1><51>: Abbrev Number: 2 (DW_TAG_base_type)
>     <52>   DW_AT_name        : REAL
>     <57>   DW_AT_byte_size   : 4
>     <58>   DW_AT_encoding    : 4        (float)
>  <1><59>: Abbrev Number: 4 (DW_TAG_subprogram)
>     <5a>   DW_AT_name        : foo
>     <5e>   DW_AT_low_pc      : 0x0
>     <66>   DW_AT_high_pc     : 128
>     <67>   DW_AT_decl_file   : 1
>     <68>   DW_AT_decl_line   : 1
>     <69>   DW_AT_external    : 1
>     <6a>   DW_AT_frame_base  : 0x0 (location list)
>  <2><72>: Abbrev Number: 5 (DW_TAG_formal_parameter)
>     <73>   DW_AT_location    : 3 byte block: 91 20 6    (DW_OP_fbreg: 32; 
> DW_OP_deref)
>     <77>   DW_AT_name        : a
>     <79>   DW_AT_type        : 0x42
>  <2><81>: Abbrev Number: 5 (DW_TAG_formal_parameter)
>     <82>   DW_AT_location    : 3 byte block: 91 28 6    (DW_OP_fbreg: 40; 
> DW_OP_deref)
>     <86>   DW_AT_name        : b
>     <88>   DW_AT_type        : 0x51
>  <2><90>: Abbrev Number: 6 (DW_TAG_entry_point)
>     <91>   DW_AT_name        : bar
>     <95>   DW_AT_low_pc      : 0x28
>     <9d>   DW_AT_decl_file   : 1
>     <9e>   DW_AT_decl_line   : 7
>     <9f>   DW_AT_frame_base  : 1 byte block: 6e         (DW_OP_reg30 
> (r30))

	Jakub