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Date: Tue, 8 Nov 2022 05:43:19 +0100
From: Nicolas Schier <n.schier@....de>
To: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Masahiro Yamada <masahiroy@...nel.org>,
Fangrui Song <maskray@...gle.com>,
Sedat Dilek <sedat.dilek@....com>,
Nathan Chancellor <nathan@...nel.org>,
Michal Marek <michal.lkml@...kovi.net>,
Nick Terrell <terrelln@...com>, Tom Rix <trix@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
Kees Cook <keescook@...omium.org>,
Josh Poimboeuf <jpoimboe@...nel.org>,
Dan Williams <dan.j.williams@...el.com>,
Miguel Ojeda <ojeda@...nel.org>,
Isabella Basso <isabbasso@...eup.net>,
Vlastimil Babka <vbabka@...e.cz>,
Rasmus Villemoes <linux@...musvillemoes.dk>,
linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
llvm@...ts.linux.dev
Subject: Re: [PATCH v2] Makefile.debug: support for -gz=zstd
On Mon, Nov 07, 2022 at 10:01:33AM -0800, Nick Desaulniers wrote:
> Make DEBUG_INFO_COMPRESSED a choice; DEBUG_INFO_UNCOMPRESSED is the
> default, DEBUG_INFO_COMPRESSED uses zlib, DEBUG_INFO_COMPRESSED_ZSTD
> uses zstd.
>
> Some quick N=1 measurements with du, /usr/bin/time -v, and bloaty:
>
> clang-16, x86_64 defconfig plus
> CONFIG_DEBUG_INFO=y CONFIG_DEBUG_INFO_UNCOMPRESSED=y:
> Elapsed (wall clock) time (h:mm:ss or m:ss): 0:55.43
> 488M vmlinux
> 27.6% 136Mi 0.0% 0 .debug_info
> 6.1% 30.2Mi 0.0% 0 .debug_str_offsets
> 3.5% 17.2Mi 0.0% 0 .debug_line
> 3.3% 16.3Mi 0.0% 0 .debug_loclists
> 0.9% 4.62Mi 0.0% 0 .debug_str
>
> clang-16, x86_64 defconfig plus
> CONFIG_DEBUG_INFO=y CONFIG_DEBUG_INFO_COMPRESSED=y (zlib):
> Elapsed (wall clock) time (h:mm:ss or m:ss): 1:00.35
> 385M vmlinux
> 21.8% 85.4Mi 0.0% 0 .debug_info
> 2.1% 8.26Mi 0.0% 0 .debug_str_offsets
> 2.1% 8.24Mi 0.0% 0 .debug_loclists
> 1.9% 7.48Mi 0.0% 0 .debug_line
> 0.5% 1.94Mi 0.0% 0 .debug_str
>
> clang-16, x86_64 defconfig plus
> CONFIG_DEBUG_INFO=y CONFIG_DEBUG_INFO_COMPRESSED_ZSTD=y (zstd):
> Elapsed (wall clock) time (h:mm:ss or m:ss): 0:59.69
> 373M vmlinux
> 21.4% 81.4Mi 0.0% 0 .debug_info
> 2.3% 8.85Mi 0.0% 0 .debug_loclists
> 1.5% 5.71Mi 0.0% 0 .debug_line
> 0.5% 1.95Mi 0.0% 0 .debug_str_offsets
> 0.4% 1.62Mi 0.0% 0 .debug_str
>
> That's only a 3.11% overall binary size savings over zlib, but at no
> performance regression.
>
> This renames the existing KConfig options:
> * DEBUG_INFO_UNCOMPRESSED -> DEBUG_INFO_COMPRESSED_NONE
> * DEBUG_INFO_COMPRESSED -> DEBUG_INFO_COMPRESSED_ZLIB
Might you want to update the DEBUG_INFO_(UN|)COMPRESSED above to the new
names?
Kind regards,
Nicolas
> So users upgrading may need to reset the new Kconfigs.
>
> Link: https://maskray.me/blog/2022-09-09-zstd-compressed-debug-sections
> Link: https://maskray.me/blog/2022-01-23-compressed-debug-sections
> Suggested-by: Sedat Dilek (DHL Supply Chain) <sedat.dilek@....com>
> Reviewed-by: Nathan Chancellor <nathan@...nel.org>
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
> ---
> Changes v1 -> v2:
> * Remove `depends on DEBUG_KERNEL` as per Nathan.
> * Rename Kconfigs as per Sedat and Masahiro.
> * Add note about renamed Kconfigs to commit message.
> * Add more help text to DEBUG_INFO_COMPRESSED_ZSTD.
>
> lib/Kconfig.debug | 29 +++++++++++++++++++++++++++--
> scripts/Makefile.debug | 4 ++++
> 2 files changed, 31 insertions(+), 2 deletions(-)
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 29280072dc0e..7c28a8fba02e 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -312,8 +312,21 @@ config DEBUG_INFO_REDUCED
> DEBUG_INFO build and compile times are reduced too.
> Only works with newer gcc versions.
>
> -config DEBUG_INFO_COMPRESSED
> - bool "Compressed debugging information"
> +choice
> + prompt "Compressed Debug information"
> + help
> + Compress the resulting debug info. Results in smaller debug info sections,
> + but requires that consumers are able to decompress the results.
> +
> + If unsure, choose DEBUG_INFO_COMPRESSED_NONE.
> +
> +config DEBUG_INFO_COMPRESSED_NONE
> + bool "Don't compress debug information"
> + help
> + Don't compress debug info sections.
> +
> +config DEBUG_INFO_COMPRESSED_ZLIB
> + bool "Compress debugging information with zlib"
> depends on $(cc-option,-gz=zlib)
> depends on $(ld-option,--compress-debug-sections=zlib)
> help
> @@ -327,6 +340,18 @@ config DEBUG_INFO_COMPRESSED
> preferable to setting $KDEB_COMPRESS to "none" which would be even
> larger.
>
> +config DEBUG_INFO_COMPRESSED_ZSTD
> + bool "Compress debugging information with zstd"
> + depends on $(cc-option,-gz=zstd)
> + depends on $(ld-option,--compress-debug-sections=zstd)
> + help
> + Compress the debug information using zstd. This may provide better
> + compression than zlib, for about the same time costs, but requires newer
> + toolchain support. Requires GCC 13.0+ or Clang 16.0+, binutils 2.40+, and
> + zstd.
> +
> +endchoice # "Compressed Debug information"
> +
> config DEBUG_INFO_SPLIT
> bool "Produce split debuginfo in .dwo files"
> depends on $(cc-option,-gsplit-dwarf)
> diff --git a/scripts/Makefile.debug b/scripts/Makefile.debug
> index 332c486f705f..8ac3379d2255 100644
> --- a/scripts/Makefile.debug
> +++ b/scripts/Makefile.debug
> @@ -31,6 +31,10 @@ ifdef CONFIG_DEBUG_INFO_COMPRESSED
> DEBUG_CFLAGS += -gz=zlib
> KBUILD_AFLAGS += -gz=zlib
> KBUILD_LDFLAGS += --compress-debug-sections=zlib
> +else ifdef CONFIG_DEBUG_INFO_COMPRESSED_ZSTD
> +DEBUG_CFLAGS += -gz=zstd
> +KBUILD_AFLAGS += -gz=zstd
> +KBUILD_LDFLAGS += --compress-debug-sections=zstd
> endif
>
> KBUILD_CFLAGS += $(DEBUG_CFLAGS)
>
> base-commit: f0c4d9fc9cc9462659728d168387191387e903cc
> --
> 2.38.1.431.g37b22c650d-goog
>
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