Re: Support objcopy changing compression to or from zstd

[Jan Beulich <jbeulich@suse.com>]

On 05.10.2022 00:01, Fangrui Song wrote:
> On 2022-10-04, Alan Modra via Binutils wrote:
>> Commit 2cac01e3ffff lacked support for objcopy changing compression
>> style.  Add that support, which meant a rewrite of
>> bfd_compress_section_contents.  In the process I've fixed some memory
>> leaks.
> 
> For objcopy --compress-debug-sections=zstd , I know that omitting
> recompression of zlib into zstd was intentional.  --compress-debug-sections=zstd 
> does not specify what to do when a section is compressed, so both (a)
> do nothing (b) re-compression with zstd are fine but I think
> avoiding recompression can avoid some complexity...
> 
> If a .o is compressed with zlib level 5, should --compress-debug-sections=zlib
> re-compress it or leave it as-is?
> 
> At any rate, I think the  objcopy --compress-debug-sections=zstd
> behavior with zlib compressed sections is mostly not interesting to a
> user.

Considering that --compress-debug-sections=none means "decompress"
rather than "leave alone" (which I would consider more reasonable),
I think it is a logical consequence that =zstd means "(re)compress"
(even if, like for =none, I'm not convinced this is the best
possible behavior). In any event, even more so now that there are
two truly distinct compression methods, I think a way to express
such variants is quite desirable, perhaps even necessary.

Jan