On Tue, May 5, 2020 at 9:47 AM Fangrui Song <maskray@xxxxxxxxxx> wrote: > > > 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 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? > > 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) Nick, I am OK with this patch. Fangrui provided the minimal requirement for --compress-debug-sections=zlib Is it worth recording in the help text? Do you want to send v2? -- Best Regards Masahiro Yamada
