Hi Thomas,
On Sun, Nov 24, 2024 at 04:58:04PM +0100, Thomas Weißschuh wrote:
> Kconfig by default chooses the first entry of a choice setting.
> For the "debug information" choice this is DEBUG_INFO_NONE which
> disables debug information completely.
>
> The kconfig choice itself recommends to use "Toolchain default":
>
> Choose which version of DWARF debug info to emit. If unsure,
> select "Toolchain default".
>
> Align the actual configuration with the recommendation by providing an
> explicit default.
>
> This also enables more codepaths from allmodconfig/allyesconfig which
> depend on debug information being available.
>
> Signed-off-by: Thomas Weißschuh <linux@xxxxxxxxxxxxxx>
> ---
> lib/Kconfig.debug | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 5d9eca035d470f7ba0c5ff932c37fd5869174269..0aefcd103d9012cd8067e5594404358b0e977644 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -240,6 +240,7 @@ config AS_HAS_NON_CONST_ULEB128
> choice
> prompt "Debug information"
> depends on DEBUG_KERNEL
> + default DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT
> help
> Selecting something other than "None" results in a kernel image
> that will include debugging info resulting in a larger kernel image.
>
> ---
> base-commit: 9f16d5e6f220661f73b36a4be1b21575651d8833
> change-id: 20241124-kbuild-allconfig_debug_info-f7449ba15be6
>
> Best regards,
> --
> Thomas Weißschuh <linux@xxxxxxxxxxxxxx>
>
I am not the biggest fan of this because it appears to have around a 5%
penalty in compilation times when I benchmarked building allmodconfig
with and without this change.
With LLVM 19.1.4:
Benchmark 1: DEBUG_INFO_NONE
Time (mean ± σ): 715.858 s ± 0.531 s [User: 38038.311 s, System: 3718.784 s]
Range (min … max): 715.271 s … 716.307 s 3 runs
Benchmark 2: DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT
Time (mean ± σ): 760.749 s ± 0.172 s [User: 40699.800 s, System: 3817.819 s]
Range (min … max): 760.617 s … 760.943 s 3 runs
Summary
DEBUG_INFO_NONE ran
1.06 ± 0.00 times faster than DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT
With GCC 14.2.0:
Benchmark 1: DEBUG_INFO_NONE
Time (mean ± σ): 830.524 s ± 0.342 s [User: 43901.642 s, System: 4515.917 s]
Range (min … max): 830.135 s … 830.777 s 3 runs
Benchmark 2: DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT
Time (mean ± σ): 873.663 s ± 0.150 s [User: 46102.416 s, System: 4968.065 s]
Range (min … max): 873.565 s … 873.836 s 3 runs
Summary
DEBUG_INFO_NONE ran
1.05 ± 0.00 times faster than DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT
I understand the desire to have CONFIG_DEBUG_INFO_BTF be selected with
allmodconfig for the sake of coverage but that is going to add up for
builders doing many builds a day.
Maybe we could add a fragment to kernel/configs for easily flipping
this? Another alternative that I have thought about recently is allowing
developers to specify a directory that holds out of tree config
fragments (KBUILD_FRAGMENTS_DIR?) that would be searched like
kernel/configs and arch/*/configs, so that people could maintain their
own fragments for easily doing something like:
allmodconfig debug_info_btf.config
during configuration. Regardless though, if others find this new default
desirable, I am fine with it.
Cheers,
Nathan
