Re: [PATCH] gas: Add --force-compress-debug-sections

[Jan Beulich <jbeulich@suse.com>]

On 23.02.2023 13:45, Tom de Vries via Binutils wrote:
> Gas has an option --compress-debug-sections that allows it to generate
> compressed debug sections.
> 
> That does not guarantee that the debug sections are in fact compressed:
> ...
> $ gcc ~/hello.c -Wa,-gdwarf-5 -c -Wa,--compress-debug-sections=zstd
> $ readelf -S -W hello.o | grep " .debug"
>   [ 9] .debug_line       PROGBITS         0000a8 000053 00      0   0  1
>   [11] .debug_line_str   PROGBITS         0000fb 000025 01  MS  0   0  1
>   [12] .debug_info       PROGBITS         000120 000039 00      0   0  1
>   [14] .debug_abbrev     PROGBITS         000159 000028 00      0   0  1
>   [15] .debug_aranges    PROGBITS         000190 000030 00      0   0 16
>   [17] .debug_str        PROGBITS         0001c0 000039 01  MS  0   0  1
> ...
> 
> Sensibly so, they're only compressed if that provides a size benefit.
> 
> However, for the purposes of testing components consuming dwarf
> we may want the sections to be compressed regardless.
> 
> Add a new option --force-compress-debug-sections that ignores the size
> heuristic, such that we have instead:
> ...
> $ gcc ~/hello.c -Wa,-gdwarf-5 -c -Wa,--compress-debug-sections=zstd \
>   -Wa,--force-compress-debug-sections
> $ readelf -S -W hello.o | grep " .debug"
>   [ 9] .debug_line       PROGBITS         0000a8 000064 00   C  0   0  8
>   [11] .debug_line_str   PROGBITS         000110 000046 01 MSC  0   0  8
>   [12] .debug_info       PROGBITS         000158 000046 00   C  0   0  8
>   [14] .debug_abbrev     PROGBITS         0001a0 000049 00   C  0   0  8
>   [15] .debug_aranges    PROGBITS         0001f0 000034 00   C  0   0  8
>   [17] .debug_str        PROGBITS         000228 00005a 01 MSC  0   0  8
> ...
> 
> Advertised as:
> ...
> $ as --help 2>&1 | grep compress
>   --compress-debug-sections[={none|zlib|zlib-gnu|zlib-gabi|zstd}]
>                           compress DWARF debug sections
>   --nocompress-debug-sections
>                           don't compress DWARF debug sections
>   --force-compress-debug-sections
>                           force compression of DWARF debug sections

No objection in principle, but have you considered making this a new
sub-option to --compress-debug-sections, i.e. compress-debug-sections=force?
(I've actually been puzzled by --nocompress-debug-sections, which looks to
be no different than --compress-debug-sections=none.)

Jan