Re: [PATCH dwarves v2 1/5] fprintf: Correct names for types with btf_type_tag attribute

[Eduard Zingerman <eddyz87@gmail.com>]

On Tue, 2023-03-28 at 12:26 -0300, Arnaldo Carvalho de Melo wrote:
[...] 
> Sure, but look:
> 
> > > -       struct qdisc_size_table *  stab;                 /*    32     8 */
> > > +       struct qdisc_size_table    stab;                 /*    32     8 */
> 
> Its the DW_TAG_pointer_type that is getting lost somehow:
> 
>  <1><b0af32>: Abbrev Number: 81 (DW_TAG_structure_type)
>     <b0af33>   DW_AT_name        : (indirect string, offset: 0xe825): Qdisc
>     <b0af37>   DW_AT_byte_size   : 384
>     <b0af39>   DW_AT_decl_file   : 223
>     <b0af3a>   DW_AT_decl_line   : 72
> 
> <SNIP>
> 
>  <2><b0af77>: Abbrev Number: 65 (DW_TAG_member)
>     <b0af78>   DW_AT_name        : (indirect string, offset: 0x4745ff): stab
>     <b0af7c>   DW_AT_type        : <0xb0b76b>
>     <b0af80>   DW_AT_decl_file   : 223
>     <b0af81>   DW_AT_decl_line   : 99
>     <b0af82>   DW_AT_data_member_location: 32
> 
> <SNIP>
> 
> <1><b0b76b>: Abbrev Number: 61 (DW_TAG_pointer_type)
>     <b0b76c>   DW_AT_type        : <0xb0b77a>
>  <2><b0b770>: Abbrev Number: 62 (User TAG value: 0x6000)
>     <b0b771>   DW_AT_name        : (indirect string, offset: 0x378): btf_type_tag
>     <b0b775>   DW_AT_const_value : (indirect string, offset: 0x6e93): rcu
>  <2><b0b779>: Abbrev Number: 0
>  <1><b0b77a>: Abbrev Number: 69 (DW_TAG_structure_type)
>     <b0b77b>   DW_AT_name        : (indirect string, offset: 0x6e5ed): qdisc_size_table
>     <b0b77f>   DW_AT_byte_size   : 64
>     <b0b780>   DW_AT_decl_file   : 223
>     <b0b781>   DW_AT_decl_line   : 56
> 
>  
> So it's all there in the DWARF info:
> 
>    b0af77 has type 0xb0b76b which is a DW_TAG_pointer_type that has type
>    0xb0b77a, that is DW_TAG_structure_type.
> 
> Now lets see how this was encoded into BTF:
> 
> [4725] STRUCT 'Qdisc' size=384 vlen=28
> <SNIP>
>         'stab' type_id=4790 bits_offset=256
> <SNIP>
> [4790] PTR '(anon)' type_id=4789
> <SNIP>
> [4789] TYPE_TAG 'rcu' type_id=4791
> <SNIP>
> [4791] STRUCT 'qdisc_size_table' size=64 vlen=5
>         'rcu' type_id=320 bits_offset=0
>         'list' type_id=87 bits_offset=128
>         'szopts' type_id=4792 bits_offset=256
>         'refcnt' type_id=16 bits_offset=448
>         'data' type_id=4659 bits_offset=480
> 
> So it all seems ok, we should keep all the info and teach fprintf to
> handle TYPE_TAG.
> 
> Which you tried, but somehow the '*' link is missing.

Yep, thanks a lot for the analysis, I will take a look.
Hopefully will send v2 tomorrow.

> 
> - Arnaldo