On Thu, May 21, 2020 at 4:36 AM 'Nick Desaulniers' via Clang Built Linux <clang-built-linux@xxxxxxxxxxxxxxxx> 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 > > For x86_64 defconfig + LLVM=1 (before): > Elapsed (wall clock) time (h:mm:ss or m:ss): 3:22.03 > Maximum resident set size (kbytes): 43856 > > For x86_64 defconfig + LLVM=1 (after): > Elapsed (wall clock) time (h:mm:ss or m:ss): 3:32.52 > Maximum resident set size (kbytes): 1566776 > > Suggested-by: David Blaikie <blakie@xxxxxxxxxx> > Suggested-by: Fangrui Song <maskray@xxxxxxxxxx> Suggested-by -> Reviewed-by https://patchwork.kernel.org/patch/11524939/#23349551 > Suggested-by: Nick Clifton <nickc@xxxxxxxxxx> I do not know where this tag came from. Nick Clifton taught us the version rule of binutils,but did not state anything about this patch itself. https://patchwork.kernel.org/patch/11524939/#23355175 > Suggested-by: Sedat Dilek <sedat.dilek@xxxxxxxxx> I do not see the source of this tag, either... > Tested-by: Sedat Dilek <sedat.dilek@xxxxxxxxx> > Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > --- snip > --- a/lib/Kconfig.debug > +++ b/lib/Kconfig.debug > @@ -225,6 +225,21 @@ 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" > + depends on DEBUG_INFO > + depends on $(cc-option,-gz=zlib) > + depends on $(as-option,-Wa,--compress-debug-sections=zlib) This does not work. (always false) You cannot enable this option. The comma between -Wa and --compress-debug-sections=zlib is eaten by Kconfig parser because commas are delimiters of function parameters. Please write like this. depends on $(as-option,-Wa$(comma)--compress-debug-sections=zlib) > + depends on $(ld-option,--compress-debug-sections=zlib) > + help > + Compress the debug information using zlib. Requires GCC 5.0+ or Clang > + 5.0+, binutils 2.26+, and zlib. > + > + Users of dpkg-deb via scripts/package/builddeb may > + wish to set the $KDEB_COMPRESS env var to "none" to avoid recompressing > + the debug info again with a different compression scheme, which can > + result in larger binaries. No. This is not correct. CONFIG_DEBUG_INFO_COMPRESSED compresses the only debug info part. The other parts still get by benefit from the default KDEB_COMPRESS=xz. The numbers are here: CONFIG_DEBUG_INFO_COMPRESSED=y -rw-r--r-- 1 masahiro masahiro 209077584 May 21 11:19 linux-image-5.7.0-rc5+-dbg_5.7.0-rc5+-26_amd64.deb CONFIG_DEBUG_INFO_COMPRESSED=y and KDEB_COMPRESS=none -rw-r--r-- 1 masahiro masahiro 643051712 May 21 11:22 linux-image-5.7.0-rc5+-dbg_5.7.0-rc5+-27_amd64.deb CONFIG_DEBUG_INFO_COMPRESSED=n -rw-r--r-- 1 masahiro masahiro 112200308 May 21 11:40 linux-image-5.7.0-rc5+-dbg_5.7.0-rc5+-30_amd64.deb For the deb package size perspective, it is better to keep KDEB_COMPRESS as default. The main motivation for changing KDEB_COMPRESS is the build speed. (see commit 1a7f0a34ea7d05) CONFIG_DEBUG_INFO_COMPRESSED has a downside for the debug deb package, but we need to accept it. -- Best Regards Masahiro Yamada
