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 TOTAL > Hi 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? 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+. > + > 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.
