On 2020-05-04, Sedat Dilek wrote:
On Mon, May 4, 2020 at 5:13 AM Nick Desaulniers <nick.desaulniers@xxxxxxxxx> wrote:As debug information gets larger and larger, it helps significantly save the size of vmlinux images to compress the information in the debug information sections. Note: this debug info is typically split off from the final compressed kernel image, which is why vmlinux is what's used in conjunction with GDB. Minimizing the debug info size should have no impact on boot times, or final compressed kernel image size. All of the debug sections will have a `C` flag set. $ readelf -S <object file> $ bloaty vmlinux.gcc75.compressed.dwarf4 -- \ vmlinux.gcc75.uncompressed.dwarf4 FILE SIZE VM SIZE -------------- -------------- +0.0% +18 [ = ] 0 [Unmapped] -73.3% -114Ki [ = ] 0 .debug_aranges -76.2% -2.01Mi [ = ] 0 .debug_frame -73.6% -2.89Mi [ = ] 0 .debug_str -80.7% -4.66Mi [ = ] 0 .debug_abbrev -82.9% -4.88Mi [ = ] 0 .debug_ranges -70.5% -9.04Mi [ = ] 0 .debug_line -79.3% -10.9Mi [ = ] 0 .debug_loc -39.5% -88.6Mi [ = ] 0 .debug_info -18.2% -123Mi [ = ] 0 TOTAL $ bloaty vmlinux.clang11.compressed.dwarf4 -- \ vmlinux.clang11.uncompressed.dwarf4 FILE SIZE VM SIZE -------------- -------------- +0.0% +23 [ = ] 0 [Unmapped] -65.6% -871 [ = ] 0 .debug_aranges -77.4% -1.84Mi [ = ] 0 .debug_frame -82.9% -2.33Mi [ = ] 0 .debug_abbrev -73.1% -2.43Mi [ = ] 0 .debug_str -84.8% -3.07Mi [ = ] 0 .debug_ranges -65.9% -8.62Mi [ = ] 0 .debug_line -86.2% -40.0Mi [ = ] 0 .debug_loc -42.0% -64.1Mi [ = ] 0 .debug_info -22.1% -122Mi [ = ] 0 TOTALHi Nick, thanks for the patch. I have slightly modified it to adapt to Linux v5.7-rc4 (what was your base?). Which linker did you use and has it an impact if you switch from ld.bfd to ld.lld?
lld has supported the linker option --compress-debug-sections=zlib since about 5.0.0 (https://reviews.llvm.org/D31941)
I tried a first normal run and in a 2nd one with CONFIG_DEBUG_INFO_COMPRESSED=y both with clang-10 and ld.lld-10. My numbers (sizes in MiB): [ diffconfig ] $ scripts/diffconfig /boot/config-5.7.0-rc4-1-amd64-clang /boot/config-5.7.0-rc4-2-amd64-clang BUILD_SALT "5.7.0-rc4-1-amd64-clang" -> "5.7.0-rc4-2-amd64-clang" +DEBUG_INFO_COMPRESSED y [ compiler and linker ] $ clang-10 -v ClangBuiltLinux clang version 10.0.1 (https://github.com/llvm/llvm-project 92d5c1be9ee93850c0a8903f05f36a23ee835dc2) Target: x86_64-unknown-linux-gnu Thread model: posix InstalledDir: /home/dileks/src/llvm-toolchain/install/bin Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/10 Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8 Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/9 Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/10 Candidate multilib: .;@m64 Candidate multilib: 32;@m32 Candidate multilib: x32;@mx32 Selected multilib: .;@m64 $ ld.lld-10 -v LLD 10.0.1 (https://github.com/llvm/llvm-project 92d5c1be9ee93850c0a8903f05f36a23ee835dc2) (compatible with GNU linkers) [ sizes vmlinux ] $ du -m 5.7.0-rc4-*/vmlinux* 409 5.7.0-rc4-1-amd64-clang/vmlinux 7 5.7.0-rc4-1-amd64-clang/vmlinux.compressed 404 5.7.0-rc4-1-amd64-clang/vmlinux.o 324 5.7.0-rc4-2-amd64-clang/vmlinux 7 5.7.0-rc4-2-amd64-clang/vmlinux.compressed 299 5.7.0-rc4-2-amd64-clang/vmlinux.o [ readelf (.debug_info as example) ] $ readelf -S vmlinux.o [33] .debug_info PROGBITS 0000000000000000 01d6a5e8 0000000006be1ee6 0000000000000000 0 0 1 $ readelf -S vmlinux.o [33] .debug_info PROGBITS 0000000000000000 01749f18 0000000002ef04d2 0000000000000000 C 0 0 1 <--- XXX: "C (compressed)" Flag Key to Flags: W (write), A (alloc), X (execute), M (merge), S (strings), I (info), L (link order), O (extra OS processing required), G (group), T (TLS), C (compressed), x (unknown), o (OS specific), E (exclude), l (large), p (processor specific) [ sizes linux-image debian packages ] $ du -m 5.7.0-rc4-*/linux-image*.deb 47 5.7.0-rc4-1-amd64-clang/linux-image-5.7.0-rc4-1-amd64-clang_5.7.0~rc4-1~bullseye+dileks1_amd64.deb 424 5.7.0-rc4-1-amd64-clang/linux-image-5.7.0-rc4-1-amd64-clang-dbg_5.7.0~rc4-1~bullseye+dileks1_amd64.deb 47 5.7.0-rc4-2-amd64-clang/linux-image-5.7.0-rc4-2-amd64-clang_5.7.0~rc4-2~bullseye+dileks1_amd64.deb 771 5.7.0-rc4-2-amd64-clang/linux-image-5.7.0-rc4-2-amd64-clang-dbg_5.7.0~rc4-2~bullseye+dileks1_amd64.deb [ sizes linux-git dir (compilation finished ] 5.7.0-rc4-1-amd64-clang: 17963 /home/dileks/src/linux-kernel/linux 5.7.0-rc4-2-amd64-clang: 14328 /home/dileks/src/linux-kernel/linux [ xz compressed linux-image-dbg packages ] $ file linux-image-5.7.0-rc4-1-amd64-clang-dbg_5.7.0~rc4-1~bullseye+dileks1_amd64.deb linux-image-5.7.0-rc4-1-amd64-clang-dbg_5.7.0~rc4-1~bullseye+dileks1_amd64.deb: Debian binary package (format 2.0), with control.tar.xz, data compression xz $ file linux-image-5.7.0-rc4-2-amd64-clang-dbg_5.7.0~rc4-2~bullseye+dileks1_amd64.deb linux-image-5.7.0-rc4-2-amd64-clang-dbg_5.7.0~rc4-2~bullseye+dileks1_amd64.deb: Debian binary package (format 2.0), with control.tar.xz, data compression xz [ file-lists ] $ dpkg --contents linux-image-5.7.0-rc4-1-amd64-clang-dbg_5.7.0~rc4-1~bullseye+dileks1_amd64.deb | wc -l 4395 $ dpkg --contents linux-image-5.7.0-rc4-2-amd64-clang-dbg_5.7.0~rc4-2~bullseye+dileks1_amd64.deb | wc -l 4395 [ file-lists vmlinux ] $ dpkg --contents linux-image-5.7.0-rc4-1-amd64-clang-dbg_5.7.0~rc4-1~bullseye+dileks1_amd64.deb | grep vmlinux -rwxr-xr-x root/root 428588312 2020-05-04 06:15 ./usr/lib/debug/lib/modules/5.7.0-rc4-1-amd64-clang/vmlinux lrwxrwxrwx root/root 0 2020-05-04 06:15 ./usr/lib/debug/boot/vmlinux-5.7.0-rc4-1-amd64-clang -> ../lib/modules/5.7.0-rc4-1-amd64-clang/vmlinux lrwxrwxrwx root/root 0 2020-05-04 06:15 ./usr/lib/debug/vmlinux-5.7.0-rc4-1-amd64-clang -> lib/modules/5.7.0-rc4-1-amd64-clang/vmlinux $ dpkg --contents linux-image-5.7.0-rc4-2-amd64-clang-dbg_5.7.0~rc4-2~bullseye+dileks1_amd64.deb | grep vmlinux -rwxr-xr-x root/root 339341456 2020-05-04 12:24 ./usr/lib/debug/lib/modules/5.7.0-rc4-2-amd64-clang/vmlinux lrwxrwxrwx root/root 0 2020-05-04 12:24 ./usr/lib/debug/boot/vmlinux-5.7.0-rc4-2-amd64-clang -> ../lib/modules/5.7.0-rc4-2-amd64-clang/vmlinux lrwxrwxrwx root/root 0 2020-05-04 12:24 ./usr/lib/debug/vmlinux-5.7.0-rc4-2-amd64-clang -> lib/modules/5.7.0-rc4-2-amd64-clang/vmlinux [ conclusion ] As you can see there is a size-reduction in case of vmlinux/vmlinux.o (debug) files... ...and my linux-git directory in total is smaller: 17963M vs. 14328M. But the resulting linux-image-dbg file is much fatter: 424M vs. 711M. XZ-compressing the gz/zlib-compressed vmlinux (debug) file results in a fatter linux-image-dbg package. For a usage of vmlinux (debug) in a VM scenario this might be nice but seen from a debian repository perspective not. For the sake of completeness: I have just installed and booted the "normal" linux-image debian package - not the debug packages. Thanks. Regards, - Sedat -Suggested-by: David Blaikie <blakie@xxxxxxxxxx> Signed-off-by: Nick Desaulniers <nick.desaulniers@xxxxxxxxx> --- Makefile | 5 +++++ lib/Kconfig.debug | 9 +++++++++ 2 files changed, 14 insertions(+) diff --git a/Makefile b/Makefile index 981eb902384b..313a054e5dc6 100644 --- a/Makefile +++ b/Makefile @@ -825,6 +825,11 @@ ifdef CONFIG_DEBUG_INFO_REDUCED DEBUG_CFLAGS += $(call cc-option, -femit-struct-debug-baseonly) \ $(call cc-option,-fno-var-tracking) endif + +ifdef CONFIG_DEBUG_INFO_COMPRESSED +DEBUG_CFLAGS += -gz=zlib +KBUILD_LDFLAGS += --compress-debug-sections=zlib +endif endif KBUILD_CFLAGS += $(DEBUG_CFLAGS) diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index f6f9a039f736..1f4a47ba6c1b 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -213,6 +213,15 @@ 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" + depends on DEBUG_INFO + depends on $(cc-option,-gz=zlib) + depends on $(ld-option,--compress-debug-sections=zlib) + help + Compress the debug information using zlib. Requires GCC 5.0+ or Clang + 5.0+. +
linker option --compress-debug-sections=zlib require binutils >= 2.26 (ld-option) Assembler option --compress-debug-sections=zlib also require binutils >= 2.26 (cc-option,-gz=zlib)
config DEBUG_INFO_SPLIT bool "Produce split debuginfo in .dwo files" depends on DEBUG_INFO -- 2.17.1 -- You received this message because you are subscribed to the Google Groups "Clang Built Linux" group. To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@xxxxxxxxxxxxxxxx. To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/20200504031340.7103-1-nick.desaulniers%40gmail.com.-- You received this message because you are subscribed to the Google Groups "Clang Built Linux" group. To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@xxxxxxxxxxxxxxxx. To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/CA%2BicZUUOaqeKeh6n4BJq2k6XQWAfNghUj57j42ZX5qyd3iOmLw%40mail.gmail.com.
