Re: [PATCH dwarves 0/4] BTF ELF writing changes

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Mon, Jan 25, 2021 at 01:06:21PM +0000, Giuliano Procida escreveu:
> Hi.
> 
> This follows on from my change to improve the error handling around
> llvm-objcopy in libbtf.c.
> 
> Note on recipients: Please let me know if I should adjust To or CC.
> 
> Note on style: I've generally placed declarations as allowed by C99,
> closest to point of use. Let me know if you'd prefer otherwise.
> 
> 1. Improve ELF error reporting

applied
 
> 2. Add .BTF section using libelf
> 
> This shows the minimal amount of code needed to drive libelf. However,
> it leaves layout up to libelf, which is almost certainly not wanted.
> 
> As an unexpcted side-effect, vmlinux is larger than before. It seems
> llvm-objcopy likes to trim down .strtab.

We have to test this thoroughly, I'm adding support to gcc's -gdwarf-5
DW_AT_data_bit_offset, I think I should get that done and release 1.20,
if some bug is still left on that new code, we can just fallback to
-gdwarf-4.

Then get back to the last 2 patches in your series, ok?

- Arnaldo
 
> 3. Manually lay out updated ELF sections
> 
> This does full layout of new and updated ELF sections. If the update
> ELF sections were not the last ones in the file by offset, then it can
> leave gaps between sections.
> 
> 4. Align .BTF section to 8 bytes
> 
> This was my original aim.
> 
> Regards.
> 
> Giuliano Procida (4):
>   btf_encoder: Improve ELF error reporting
>   btf_encoder: Add .BTF section using libelf
>   btf_encoder: Manually lay out updated ELF sections
>   btf_encoder: Align .BTF section to 8 bytes
> 
>  libbtf.c | 222 +++++++++++++++++++++++++++++++++++++++++++------------
>  1 file changed, 175 insertions(+), 47 deletions(-)
> 
> -- 
> 2.30.0.280.ga3ce27912f-goog
> 

-- 

- Arnaldo