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Subject[PATCH v2] Makefile.debug: support for -gz=zstd
From
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
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@dhl.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.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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