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Makefile: support compressed debug info

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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

Thanks to:
Nick Clifton helped us to provide the minimal binutils version.
Sedat Dilek found an increase in size of debug .deb package.

Cc: Nick Clifton <nickc@redhat.com>
Suggested-by: David Blaikie <blaikie@google.com>
Reviewed-by: Fangrui Song <maskray@google.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
This commit is contained in:
Nick Desaulniers 2020-05-26 10:18:29 -07:00 committed by Masahiro Yamada
parent 565587d8d5
commit 10e68b02c8
2 changed files with 23 additions and 0 deletions
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6
Makefile
View File

@ -825,6 +825,12 @@ 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_AFLAGS += -Wa,--compress-debug-sections=zlib
KBUILD_LDFLAGS += --compress-debug-sections=zlib
endif
KBUILD_CFLAGS += $(DEBUG_CFLAGS)
export DEBUG_CFLAGS

17
lib/Kconfig.debug
View File

@ -213,6 +213,23 @@ 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 $(as-option,-Wa$(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 find an increase in
size of their debug .deb packages with this config set, due to the
debug info being compressed with zlib, then the object files being
recompressed with a different compression scheme. But this is still
preferable to setting $KDEB_COMPRESS to "none" which would be even
larger.
config DEBUG_INFO_SPLIT
bool "Produce split debuginfo in .dwo files"
depends on DEBUG_INFO