Re: [PATCH V2] dwarf.exp: Allow generating a stub .debug_line section

[Yao Qi <qiyaoltc at gmail dot com>]

On 02/23/2015 02:46 PM, Petr Machata wrote:
> This is what I wrote last week, and it all still holds:
> 
> like GDB itself, dwgrep uses dwarf.exp to fabricate Dwarfs for its test
> cases.  For one test case, I need to create a stub .debug_line section
> and reference files defined therein from DW_AT_decl_file.  Hence this
> patch, which implements generating barest minimum of .debug_line.
> 
> I suspect this could be useful for GDB as well, git grep showed me some
> .exp's creating .debug_line by hand, but I didn't really take a close
> look.

Yeah, it is useful to GDB.

> 
> There were no regressions on x86_64.
> 

but the new macro you added isn't used by any test cases.

> Example of use:
> 
> 	Dwarf::assemble "foo.s" {
> 	    build_id 0102030405060708
> 
> 	    cu {is_64 0 version 4 addr_size 8} {
> 		DW_TAG_compile_unit {
> 		    {MACRO_AT_stmt_list {

Is there any reason you decide to implement this attribute as a macro
attribute?  DW_AT_stmt_list attribute itself is quite simple, whose
value is a section offset to the .debug_line section, so we don't need
to bother macro attribute, which doesn't exist in dwarf spec but are
used to generate some dwarf attributes.

I'd like DW_AT_stmt_list implemented in the same way as other
attributes, for example,

  cu {is_64 0 version 4 addr_size 8} {
    compile_unit {
      { stmt_list $label1 sec_offset}
    }
    ...
    label1: line_number_info {
        line_number_program_header {
        }
        line_number_program {
        }
    }
  }

what do you think?

> 			{include "foo"}
> 			{file_name "foo.c" 1}
> 		    }}
> 		} {
> 		    DW_TAG_subprogram {
> 			# We can now reference the source file.
> 			{DW_AT_decl_file 1 DW_FORM_data1}
> 		    }
> 		}
> 	    }
> 	}
> 
> I do not have commit rights, so if this patch is acceptable, I will need
> someone to commit this for me.

Why don't you apply for an account for you?  It is easy to do so
https://sourceware.org/cgi-bin/pdw/ps_form.cgi I (yao.qi@arm.com) could
be the people to approve your request.

> @@ -422,6 +435,11 @@ namespace eval Dwarf {
>  		_op .${size}byte $value
>  	    }
>  
> +	    DW_FORM_sec_offset {
> +		variable _cu_offset_size
> +		_op .${_cu_offset_size}byte $value
> +	    }
> +
>  	    DW_FORM_ref1 -
>  	    DW_FORM_flag -
>  	    DW_FORM_data1 {
> @@ -494,7 +512,6 @@ namespace eval Dwarf {
>  
>  	    DW_FORM_ref2 -
>  	    DW_FORM_indirect -
> -	    DW_FORM_sec_offset -
>  	    DW_FORM_exprloc -

This part looks right to me, and DW_FORM_sec_offset can be used by
other attributes too, such as DW_AT_ranges.

-- 
Yao