Makefile.debug: support for -gz=zstd

Make DEBUG_INFO_COMPRESSED a choice; DEBUG_INFO_COMPRESSED_NONE is the
default, DEBUG_INFO_COMPRESSED_ZLIB uses zlib,
DEBUG_INFO_COMPRESSED_ZSTD uses zstd.

This renames the existing KConfig option DEBUG_INFO_COMPRESSED to
DEBUG_INFO_COMPRESSED_ZLIB so users upgrading may need to reset the new
Kconfigs.

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_COMPRESSED_NONE=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_ZLIB=y:
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:
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.

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>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index c3c0b077ade33c4b7240a4b5247cfc02e5c71182..d93dbe5a1d143659a10f16b952edb5f58d8c488e 100644 (file)
--- 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 332c486f705f75edb63fd06f412c3563733e3814..059ff38fe0cb31e8646d5b9228fe89219d881bf8 100644 (file)
--- a/scripts/Makefile.debug
+++ b/scripts/Makefile.debug
@@ -27,10 +27,14 @@ else
 DEBUG_RUSTFLAGS        += -Cdebuginfo=2
 endif
 
-ifdef CONFIG_DEBUG_INFO_COMPRESSED
+ifdef CONFIG_DEBUG_INFO_COMPRESSED_ZLIB
 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)