* [PATCH v5] x86: Avoid relocation information in final vmlinux @ 2023-03-20 12:10 Petr Pavlu 2023-03-20 18:35 ` Nick Desaulniers 2023-03-20 20:12 ` Dave Hansen 0 siblings, 2 replies; 7+ messages in thread From: Petr Pavlu @ 2023-03-20 12:10 UTC (permalink / raw) To: tglx, mingo, bp, dave.hansen, x86, hpa Cc: nathan, ndesaulniers, trix, corbet, linux-kernel, Petr Pavlu The Linux build process on x86 roughly consists of compiling all input files, statically linking them into a vmlinux ELF file, and then taking and turning this file into an actual bzImage bootable file. vmlinux has in this process two main purposes: 1) It is an intermediate build target on the way to produce the final bootable image. 2) It is a file that is expected to be used by debuggers and standard ELF tooling to work with the built kernel. For the second purpose, a vmlinux file is typically collected by various package build recipes, such as distribution spec files, including the kernel's own tar-pkg target. When building a kernel supporting KASLR with CONFIG_X86_NEED_RELOCS, vmlinux contains also relocation information produced by using the --emit-relocs linker option. This is utilized by subsequent build steps to create vmlinux.relocs and produce a relocatable image. However, the information is not needed by debuggers and other standard ELF tooling. The issue is then that the collected vmlinux file and hence distribution packages end up unnecessarily large because of this extra data. The following is a size comparison of vmlinux v6.0 with and without the relocation information: | Configuration | With relocs | Stripped relocs | | x86_64_defconfig | 70 MB | 43 MB | | +CONFIG_DEBUG_INFO | 818 MB | 367 MB | Optimize a resulting vmlinux by adding a postlink step that splits the relocation information into vmlinux.relocs and then strips it from the vmlinux binary. Signed-off-by: Petr Pavlu <petr.pavlu@suse.com> --- Changes since v4 [1]: - Update the example target which is mentioned in the patch description to collect vmlinux from binrpm-pkg to tar-pkg, to reflect fc8c2d8ff206 ("kbuild: Stop including vmlinux.bz2 in the rpm's"). Changes since v3 [2]: - Update the Kbuild.include path in arch/x86/Makefile.postlink to work after 67d7c3023a67 ("kbuild: remove --include-dir MAKEFLAG from top Makefile"). Changes since v2 [3]: - Ignore only the moved vmlinux.relocs, add it to .gitignore and Documentation/dontdiff. - Clean up the patch description. Changes since v1 [4]: - Fix the command to remove relocations to work with llvm-objcopy too. [1] https://lore.kernel.org/lkml/20230227131829.26824-1-petr.pavlu@suse.com/ [2] https://lore.kernel.org/lkml/20221211141227.7622-1-petr.pavlu@suse.com/ [3] https://lore.kernel.org/lkml/20220927084632.14531-1-petr.pavlu@suse.com/ [4] https://lore.kernel.org/lkml/20220913132911.6850-1-petr.pavlu@suse.com/ .gitignore | 1 + Documentation/dontdiff | 1 + arch/x86/Makefile.postlink | 41 +++++++++++++++++++++++++++++ arch/x86/boot/compressed/.gitignore | 1 - arch/x86/boot/compressed/Makefile | 10 +++---- 5 files changed, 47 insertions(+), 7 deletions(-) create mode 100644 arch/x86/Makefile.postlink diff --git a/.gitignore b/.gitignore index 70ec6037fa7a..9bafd3c6bb5f 100644 --- a/.gitignore +++ b/.gitignore @@ -65,6 +65,7 @@ modules.order /vmlinux /vmlinux.32 /vmlinux.map +/vmlinux.relocs /vmlinux.symvers /vmlinux-gdb.py /vmlinuz diff --git a/Documentation/dontdiff b/Documentation/dontdiff index 3c399f132e2d..a62ad01e6d11 100644 --- a/Documentation/dontdiff +++ b/Documentation/dontdiff @@ -254,6 +254,7 @@ vmlinux.aout vmlinux.bin.all vmlinux.lds vmlinux.map +vmlinux.relocs vmlinux.symvers vmlinuz voffset.h diff --git a/arch/x86/Makefile.postlink b/arch/x86/Makefile.postlink new file mode 100644 index 000000000000..195af937aa4d --- /dev/null +++ b/arch/x86/Makefile.postlink @@ -0,0 +1,41 @@ +# SPDX-License-Identifier: GPL-2.0 +# =========================================================================== +# Post-link x86 pass +# =========================================================================== +# +# 1. Separate relocations from vmlinux into vmlinux.relocs. +# 2. Strip relocations from vmlinux. + +PHONY := __archpost +__archpost: + +-include include/config/auto.conf +include $(srctree)/scripts/Kbuild.include + +CMD_RELOCS = arch/x86/tools/relocs +quiet_cmd_relocs = RELOCS $@.relocs + cmd_relocs = $(CMD_RELOCS) $@ > $@.relocs;$(CMD_RELOCS) --abs-relocs $@ + +quiet_cmd_strip_relocs = RSTRIP $@ + cmd_strip_relocs = $(OBJCOPY) --remove-section='.rel.*' --remove-section='.rel__*' --remove-section='.rela.*' --remove-section='.rela__*' $@ + +# `@true` prevents complaint when there is nothing to be done + +vmlinux: FORCE + @true +ifeq ($(CONFIG_X86_NEED_RELOCS),y) + $(call cmd,relocs) + $(call cmd,strip_relocs) +endif + +%.ko: FORCE + @true + +clean: + @rm -f vmlinux.relocs + +PHONY += FORCE clean + +FORCE: + +.PHONY: $(PHONY) diff --git a/arch/x86/boot/compressed/.gitignore b/arch/x86/boot/compressed/.gitignore index 25805199a506..b2968175fc27 100644 --- a/arch/x86/boot/compressed/.gitignore +++ b/arch/x86/boot/compressed/.gitignore @@ -1,7 +1,6 @@ # SPDX-License-Identifier: GPL-2.0-only relocs vmlinux.bin.all -vmlinux.relocs vmlinux.lds mkpiggy piggy.S diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile index 6b6cfe607bdb..19d1fb601796 100644 --- a/arch/x86/boot/compressed/Makefile +++ b/arch/x86/boot/compressed/Makefile @@ -121,14 +121,12 @@ $(obj)/vmlinux.bin: vmlinux FORCE targets += $(patsubst $(obj)/%,%,$(vmlinux-objs-y)) vmlinux.bin.all vmlinux.relocs -CMD_RELOCS = arch/x86/tools/relocs -quiet_cmd_relocs = RELOCS $@ - cmd_relocs = $(CMD_RELOCS) $< > $@;$(CMD_RELOCS) --abs-relocs $< -$(obj)/vmlinux.relocs: vmlinux FORCE - $(call if_changed,relocs) +# vmlinux.relocs is created by the vmlinux postlink step. +vmlinux.relocs: vmlinux + @true vmlinux.bin.all-y := $(obj)/vmlinux.bin -vmlinux.bin.all-$(CONFIG_X86_NEED_RELOCS) += $(obj)/vmlinux.relocs +vmlinux.bin.all-$(CONFIG_X86_NEED_RELOCS) += vmlinux.relocs $(obj)/vmlinux.bin.gz: $(vmlinux.bin.all-y) FORCE $(call if_changed,gzip) -- 2.35.3 ^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH v5] x86: Avoid relocation information in final vmlinux 2023-03-20 12:10 [PATCH v5] x86: Avoid relocation information in final vmlinux Petr Pavlu @ 2023-03-20 18:35 ` Nick Desaulniers 2023-03-21 11:57 ` Borislav Petkov 2023-03-24 10:30 ` Petr Pavlu 2023-03-20 20:12 ` Dave Hansen 1 sibling, 2 replies; 7+ messages in thread From: Nick Desaulniers @ 2023-03-20 18:35 UTC (permalink / raw) To: Petr Pavlu Cc: tglx, mingo, bp, dave.hansen, x86, hpa, nathan, trix, corbet, linux-kernel, clang-built-linux, linux-toolchains, Fangrui Song On Mon, Mar 20, 2023 at 5:10 AM Petr Pavlu <petr.pavlu@suse.com> wrote: > > The Linux build process on x86 roughly consists of compiling all input > files, statically linking them into a vmlinux ELF file, and then taking > and turning this file into an actual bzImage bootable file. > > vmlinux has in this process two main purposes: > 1) It is an intermediate build target on the way to produce the final > bootable image. > 2) It is a file that is expected to be used by debuggers and standard > ELF tooling to work with the built kernel. > > For the second purpose, a vmlinux file is typically collected by various > package build recipes, such as distribution spec files, including the > kernel's own tar-pkg target. > > When building a kernel supporting KASLR with CONFIG_X86_NEED_RELOCS, > vmlinux contains also relocation information produced by using the > --emit-relocs linker option. This is utilized by subsequent build steps > to create vmlinux.relocs and produce a relocatable image. However, the > information is not needed by debuggers and other standard ELF tooling. > > The issue is then that the collected vmlinux file and hence distribution > packages end up unnecessarily large because of this extra data. The > following is a size comparison of vmlinux v6.0 with and without the > relocation information: > | Configuration | With relocs | Stripped relocs | > | x86_64_defconfig | 70 MB | 43 MB | > | +CONFIG_DEBUG_INFO | 818 MB | 367 MB | Thanks for getting this to work with llvm-objcopy. It's a pretty big win for us, especially for thin-lto builds which produce a ridiculous amount of debug info duplication (something I'm petitioning our DWARF folks to look into for DWARFv6) some measurements (all LLVM=1): Before this patch: defconfig: 76M vmlinux DEBUG_INFO: 510M vmlinux DEBUG_INFO+LTO_CLANG_THIN: 796M vmlinux after: defconfig: 48M vmlinux (-36.8%) DEBUG_INFO: 270M vmlinux (-47%) LTO_CLANG_THIN: 400M vmlinux (-49.8%) So basically a 50% reduction in vmlinux size, depending on the precise configs selected. That's pretty great! Android usually keeps around vmlinux artifacts as well as the compressed image in case we need to debug the image later, this should help us cut our storage costs for those quite a bit. arm64 is more common for Android, but x86_64 is pretty helpful for a virtualized target; we do use it alot for first party development. I also tested that I could still boot the result in QEMU, attach GDB, and still hit breakpoints in the resulting vmlinux. I also tested that there were no more rel/rela sections missed in the resulting vmlinux images. Tested-by: Nick Desaulniers <ndesaulniers@google.com> Some minor review comments below. I do also wonder if linkers have something like --emit-relocs, but the option to produce it in an additional file. That would help us avoid producing it only to split it out in the first place. > > Optimize a resulting vmlinux by adding a postlink step that splits the > relocation information into vmlinux.relocs and then strips it from the > vmlinux binary. > > Signed-off-by: Petr Pavlu <petr.pavlu@suse.com> > --- > > Changes since v4 [1]: > - Update the example target which is mentioned in the patch description > to collect vmlinux from binrpm-pkg to tar-pkg, to reflect fc8c2d8ff206 > ("kbuild: Stop including vmlinux.bz2 in the rpm's"). > > Changes since v3 [2]: > - Update the Kbuild.include path in arch/x86/Makefile.postlink to work > after 67d7c3023a67 ("kbuild: remove --include-dir MAKEFLAG from top > Makefile"). > > Changes since v2 [3]: > - Ignore only the moved vmlinux.relocs, add it to .gitignore and > Documentation/dontdiff. > - Clean up the patch description. > > Changes since v1 [4]: > - Fix the command to remove relocations to work with llvm-objcopy too. > > [1] https://lore.kernel.org/lkml/20230227131829.26824-1-petr.pavlu@suse.com/ > [2] https://lore.kernel.org/lkml/20221211141227.7622-1-petr.pavlu@suse.com/ > [3] https://lore.kernel.org/lkml/20220927084632.14531-1-petr.pavlu@suse.com/ > [4] https://lore.kernel.org/lkml/20220913132911.6850-1-petr.pavlu@suse.com/ > > .gitignore | 1 + > Documentation/dontdiff | 1 + > arch/x86/Makefile.postlink | 41 +++++++++++++++++++++++++++++ > arch/x86/boot/compressed/.gitignore | 1 - > arch/x86/boot/compressed/Makefile | 10 +++---- > 5 files changed, 47 insertions(+), 7 deletions(-) > create mode 100644 arch/x86/Makefile.postlink > > diff --git a/.gitignore b/.gitignore > index 70ec6037fa7a..9bafd3c6bb5f 100644 > --- a/.gitignore > +++ b/.gitignore > @@ -65,6 +65,7 @@ modules.order > /vmlinux > /vmlinux.32 > /vmlinux.map > +/vmlinux.relocs Why do you move this from the arch/x86/boot/compressed/ dir? > /vmlinux.symvers > /vmlinux-gdb.py > /vmlinuz > diff --git a/Documentation/dontdiff b/Documentation/dontdiff > index 3c399f132e2d..a62ad01e6d11 100644 > --- a/Documentation/dontdiff > +++ b/Documentation/dontdiff > @@ -254,6 +254,7 @@ vmlinux.aout > vmlinux.bin.all > vmlinux.lds > vmlinux.map > +vmlinux.relocs > vmlinux.symvers > vmlinuz > voffset.h > diff --git a/arch/x86/Makefile.postlink b/arch/x86/Makefile.postlink > new file mode 100644 > index 000000000000..195af937aa4d > --- /dev/null > +++ b/arch/x86/Makefile.postlink > @@ -0,0 +1,41 @@ > +# SPDX-License-Identifier: GPL-2.0 > +# =========================================================================== > +# Post-link x86 pass > +# =========================================================================== > +# > +# 1. Separate relocations from vmlinux into vmlinux.relocs. > +# 2. Strip relocations from vmlinux. > + > +PHONY := __archpost > +__archpost: > + > +-include include/config/auto.conf > +include $(srctree)/scripts/Kbuild.include > + > +CMD_RELOCS = arch/x86/tools/relocs > +quiet_cmd_relocs = RELOCS $@.relocs > + cmd_relocs = $(CMD_RELOCS) $@ > $@.relocs;$(CMD_RELOCS) --abs-relocs $@ > + > +quiet_cmd_strip_relocs = RSTRIP $@ > + cmd_strip_relocs = $(OBJCOPY) --remove-section='.rel.*' --remove-section='.rel__*' --remove-section='.rela.*' --remove-section='.rela__*' $@ This line is pretty long (146 chars), can you use \ here to wrap it? > + > +# `@true` prevents complaint when there is nothing to be done > + > +vmlinux: FORCE > + @true > +ifeq ($(CONFIG_X86_NEED_RELOCS),y) > + $(call cmd,relocs) > + $(call cmd,strip_relocs) > +endif > + > +%.ko: FORCE > + @true > + > +clean: > + @rm -f vmlinux.relocs > + > +PHONY += FORCE clean > + > +FORCE: > + > +.PHONY: $(PHONY) > diff --git a/arch/x86/boot/compressed/.gitignore b/arch/x86/boot/compressed/.gitignore > index 25805199a506..b2968175fc27 100644 > --- a/arch/x86/boot/compressed/.gitignore > +++ b/arch/x86/boot/compressed/.gitignore > @@ -1,7 +1,6 @@ > # SPDX-License-Identifier: GPL-2.0-only > relocs > vmlinux.bin.all > -vmlinux.relocs > vmlinux.lds > mkpiggy > piggy.S > diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile > index 6b6cfe607bdb..19d1fb601796 100644 > --- a/arch/x86/boot/compressed/Makefile > +++ b/arch/x86/boot/compressed/Makefile > @@ -121,14 +121,12 @@ $(obj)/vmlinux.bin: vmlinux FORCE > > targets += $(patsubst $(obj)/%,%,$(vmlinux-objs-y)) vmlinux.bin.all vmlinux.relocs > > -CMD_RELOCS = arch/x86/tools/relocs > -quiet_cmd_relocs = RELOCS $@ > - cmd_relocs = $(CMD_RELOCS) $< > $@;$(CMD_RELOCS) --abs-relocs $< > -$(obj)/vmlinux.relocs: vmlinux FORCE > - $(call if_changed,relocs) > +# vmlinux.relocs is created by the vmlinux postlink step. > +vmlinux.relocs: vmlinux > + @true > > vmlinux.bin.all-y := $(obj)/vmlinux.bin > -vmlinux.bin.all-$(CONFIG_X86_NEED_RELOCS) += $(obj)/vmlinux.relocs > +vmlinux.bin.all-$(CONFIG_X86_NEED_RELOCS) += vmlinux.relocs Why do you remove $(obj) here? I'm guessing that's why you moved vmlinux.relocs between .gitignore files? > > $(obj)/vmlinux.bin.gz: $(vmlinux.bin.all-y) FORCE > $(call if_changed,gzip) > -- > 2.35.3 > -- Thanks, ~Nick Desaulniers ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v5] x86: Avoid relocation information in final vmlinux 2023-03-20 18:35 ` Nick Desaulniers @ 2023-03-21 11:57 ` Borislav Petkov 2023-03-24 10:31 ` Petr Pavlu 2023-03-24 10:30 ` Petr Pavlu 1 sibling, 1 reply; 7+ messages in thread From: Borislav Petkov @ 2023-03-21 11:57 UTC (permalink / raw) To: Nick Desaulniers Cc: Petr Pavlu, tglx, mingo, dave.hansen, x86, hpa, nathan, trix, corbet, linux-kernel, clang-built-linux, linux-toolchains, Fangrui Song On Mon, Mar 20, 2023 at 11:35:30AM -0700, Nick Desaulniers wrote: > Why do you move this from the arch/x86/boot/compressed/ dir? I got an explanation here: https://lore.kernel.org/r/16941b45-0f4f-e7c9-4602-d9acb0c612c3@suse.com but my counterargument is: vmlinux.relocs is used there, in that dir, so it should stay there just like the rest of the by-products generated there. Thx. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v5] x86: Avoid relocation information in final vmlinux 2023-03-21 11:57 ` Borislav Petkov @ 2023-03-24 10:31 ` Petr Pavlu 0 siblings, 0 replies; 7+ messages in thread From: Petr Pavlu @ 2023-03-24 10:31 UTC (permalink / raw) To: Borislav Petkov, Nick Desaulniers Cc: tglx, mingo, dave.hansen, x86, hpa, nathan, trix, corbet, linux-kernel, clang-built-linux, linux-toolchains, Fangrui Song On 3/21/23 12:57, Borislav Petkov wrote: > On Mon, Mar 20, 2023 at 11:35:30AM -0700, Nick Desaulniers wrote: >> Why do you move this from the arch/x86/boot/compressed/ dir? > > I got an explanation here: > > https://lore.kernel.org/r/16941b45-0f4f-e7c9-4602-d9acb0c612c3@suse.com > > but my counterargument is: > > vmlinux.relocs is used there, in that dir, so it should stay there just > like the rest of the by-products generated there. Ok, I can see this argument. I will update it and post a new version. Thanks, Petr ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v5] x86: Avoid relocation information in final vmlinux 2023-03-20 18:35 ` Nick Desaulniers 2023-03-21 11:57 ` Borislav Petkov @ 2023-03-24 10:30 ` Petr Pavlu 1 sibling, 0 replies; 7+ messages in thread From: Petr Pavlu @ 2023-03-24 10:30 UTC (permalink / raw) To: Nick Desaulniers Cc: tglx, mingo, bp, dave.hansen, x86, hpa, nathan, trix, corbet, linux-kernel, clang-built-linux, linux-toolchains, Fangrui Song On 3/20/23 19:35, Nick Desaulniers wrote: > On Mon, Mar 20, 2023 at 5:10 AM Petr Pavlu <petr.pavlu@suse.com> wrote: >> >> The Linux build process on x86 roughly consists of compiling all input >> files, statically linking them into a vmlinux ELF file, and then taking >> and turning this file into an actual bzImage bootable file. >> >> vmlinux has in this process two main purposes: >> 1) It is an intermediate build target on the way to produce the final >> bootable image. >> 2) It is a file that is expected to be used by debuggers and standard >> ELF tooling to work with the built kernel. >> >> For the second purpose, a vmlinux file is typically collected by various >> package build recipes, such as distribution spec files, including the >> kernel's own tar-pkg target. >> >> When building a kernel supporting KASLR with CONFIG_X86_NEED_RELOCS, >> vmlinux contains also relocation information produced by using the >> --emit-relocs linker option. This is utilized by subsequent build steps >> to create vmlinux.relocs and produce a relocatable image. However, the >> information is not needed by debuggers and other standard ELF tooling. >> >> The issue is then that the collected vmlinux file and hence distribution >> packages end up unnecessarily large because of this extra data. The >> following is a size comparison of vmlinux v6.0 with and without the >> relocation information: >> | Configuration | With relocs | Stripped relocs | >> | x86_64_defconfig | 70 MB | 43 MB | >> | +CONFIG_DEBUG_INFO | 818 MB | 367 MB | > > Thanks for getting this to work with llvm-objcopy. It's a pretty big > win for us, especially for thin-lto builds which produce a ridiculous > amount of debug info duplication (something I'm petitioning our DWARF > folks to look into for DWARFv6) some measurements (all LLVM=1): > > Before this patch: > defconfig: > 76M vmlinux > DEBUG_INFO: > 510M vmlinux > DEBUG_INFO+LTO_CLANG_THIN: > 796M vmlinux > > after: > defconfig: > 48M vmlinux (-36.8%) > DEBUG_INFO: > 270M vmlinux (-47%) > LTO_CLANG_THIN: > 400M vmlinux (-49.8%) > > So basically a 50% reduction in vmlinux size, depending on the precise > configs selected. That's pretty great! > > Android usually keeps around vmlinux artifacts as well as the > compressed image in case we need to debug the image later, this should > help us cut our storage costs for those quite a bit. arm64 is more > common for Android, but x86_64 is pretty helpful for a virtualized > target; we do use it alot for first party development. > > I also tested that I could still boot the result in QEMU, attach GDB, > and still hit breakpoints in the resulting vmlinux. I also tested > that there were no more rel/rela sections missed in the resulting > vmlinux images. > > Tested-by: Nick Desaulniers <ndesaulniers@google.com> Thanks for testing this change. > > Some minor review comments below. > > > I do also wonder if linkers have something like --emit-relocs, but the > option to produce it in an additional file. That would help us avoid > producing it only to split it out in the first place. I'm afraid I'm not aware of such an option. > >> >> Optimize a resulting vmlinux by adding a postlink step that splits the >> relocation information into vmlinux.relocs and then strips it from the >> vmlinux binary. >> >> Signed-off-by: Petr Pavlu <petr.pavlu@suse.com> >> --- >> >> Changes since v4 [1]: >> - Update the example target which is mentioned in the patch description >> to collect vmlinux from binrpm-pkg to tar-pkg, to reflect fc8c2d8ff206 >> ("kbuild: Stop including vmlinux.bz2 in the rpm's"). >> >> Changes since v3 [2]: >> - Update the Kbuild.include path in arch/x86/Makefile.postlink to work >> after 67d7c3023a67 ("kbuild: remove --include-dir MAKEFLAG from top >> Makefile"). >> >> Changes since v2 [3]: >> - Ignore only the moved vmlinux.relocs, add it to .gitignore and >> Documentation/dontdiff. >> - Clean up the patch description. >> >> Changes since v1 [4]: >> - Fix the command to remove relocations to work with llvm-objcopy too. >> >> [1] https://lore.kernel.org/lkml/20230227131829.26824-1-petr.pavlu@suse.com/ >> [2] https://lore.kernel.org/lkml/20221211141227.7622-1-petr.pavlu@suse.com/ >> [3] https://lore.kernel.org/lkml/20220927084632.14531-1-petr.pavlu@suse.com/ >> [4] https://lore.kernel.org/lkml/20220913132911.6850-1-petr.pavlu@suse.com/ >> >> .gitignore | 1 + >> Documentation/dontdiff | 1 + >> arch/x86/Makefile.postlink | 41 +++++++++++++++++++++++++++++ >> arch/x86/boot/compressed/.gitignore | 1 - >> arch/x86/boot/compressed/Makefile | 10 +++---- >> 5 files changed, 47 insertions(+), 7 deletions(-) >> create mode 100644 arch/x86/Makefile.postlink >> >> diff --git a/.gitignore b/.gitignore >> index 70ec6037fa7a..9bafd3c6bb5f 100644 >> --- a/.gitignore >> +++ b/.gitignore >> @@ -65,6 +65,7 @@ modules.order >> /vmlinux >> /vmlinux.32 >> /vmlinux.map >> +/vmlinux.relocs > > Why do you move this from the arch/x86/boot/compressed/ dir? The idea was for Makefile.postlink to produce its output at own $(obj) level which is essentially the top objtree directory. However, I can see the argument to write vmlinux.relocs in the same directory where other related output files are present. > >> /vmlinux.symvers >> /vmlinux-gdb.py >> /vmlinuz >> diff --git a/Documentation/dontdiff b/Documentation/dontdiff >> index 3c399f132e2d..a62ad01e6d11 100644 >> --- a/Documentation/dontdiff >> +++ b/Documentation/dontdiff >> @@ -254,6 +254,7 @@ vmlinux.aout >> vmlinux.bin.all >> vmlinux.lds >> vmlinux.map >> +vmlinux.relocs >> vmlinux.symvers >> vmlinuz >> voffset.h >> diff --git a/arch/x86/Makefile.postlink b/arch/x86/Makefile.postlink >> new file mode 100644 >> index 000000000000..195af937aa4d >> --- /dev/null >> +++ b/arch/x86/Makefile.postlink >> @@ -0,0 +1,41 @@ >> +# SPDX-License-Identifier: GPL-2.0 >> +# =========================================================================== >> +# Post-link x86 pass >> +# =========================================================================== >> +# >> +# 1. Separate relocations from vmlinux into vmlinux.relocs. >> +# 2. Strip relocations from vmlinux. >> + >> +PHONY := __archpost >> +__archpost: >> + >> +-include include/config/auto.conf >> +include $(srctree)/scripts/Kbuild.include >> + >> +CMD_RELOCS = arch/x86/tools/relocs >> +quiet_cmd_relocs = RELOCS $@.relocs >> + cmd_relocs = $(CMD_RELOCS) $@ > $@.relocs;$(CMD_RELOCS) --abs-relocs $@ >> + >> +quiet_cmd_strip_relocs = RSTRIP $@ >> + cmd_strip_relocs = $(OBJCOPY) --remove-section='.rel.*' --remove-section='.rel__*' --remove-section='.rela.*' --remove-section='.rela__*' $@ > > This line is pretty long (146 chars), can you use \ here to wrap it? Ack, I'll wrap it in a new version. >> + >> +# `@true` prevents complaint when there is nothing to be done >> + >> +vmlinux: FORCE >> + @true >> +ifeq ($(CONFIG_X86_NEED_RELOCS),y) >> + $(call cmd,relocs) >> + $(call cmd,strip_relocs) >> +endif >> + >> +%.ko: FORCE >> + @true >> + >> +clean: >> + @rm -f vmlinux.relocs >> + >> +PHONY += FORCE clean >> + >> +FORCE: >> + >> +.PHONY: $(PHONY) >> diff --git a/arch/x86/boot/compressed/.gitignore b/arch/x86/boot/compressed/.gitignore >> index 25805199a506..b2968175fc27 100644 >> --- a/arch/x86/boot/compressed/.gitignore >> +++ b/arch/x86/boot/compressed/.gitignore >> @@ -1,7 +1,6 @@ >> # SPDX-License-Identifier: GPL-2.0-only >> relocs >> vmlinux.bin.all >> -vmlinux.relocs >> vmlinux.lds >> mkpiggy >> piggy.S >> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile >> index 6b6cfe607bdb..19d1fb601796 100644 >> --- a/arch/x86/boot/compressed/Makefile >> +++ b/arch/x86/boot/compressed/Makefile >> @@ -121,14 +121,12 @@ $(obj)/vmlinux.bin: vmlinux FORCE >> >> targets += $(patsubst $(obj)/%,%,$(vmlinux-objs-y)) vmlinux.bin.all vmlinux.relocs >> >> -CMD_RELOCS = arch/x86/tools/relocs >> -quiet_cmd_relocs = RELOCS $@ >> - cmd_relocs = $(CMD_RELOCS) $< > $@;$(CMD_RELOCS) --abs-relocs $< >> -$(obj)/vmlinux.relocs: vmlinux FORCE >> - $(call if_changed,relocs) >> +# vmlinux.relocs is created by the vmlinux postlink step. >> +vmlinux.relocs: vmlinux >> + @true >> >> vmlinux.bin.all-y := $(obj)/vmlinux.bin >> -vmlinux.bin.all-$(CONFIG_X86_NEED_RELOCS) += $(obj)/vmlinux.relocs >> +vmlinux.bin.all-$(CONFIG_X86_NEED_RELOCS) += vmlinux.relocs > > Why do you remove $(obj) here? I'm guessing that's why you moved > vmlinux.relocs between .gitignore files? Yes, it is because this version of Makefile.postlink saves vmlinux.relocs in the top objtree directory. Thanks, Petr ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v5] x86: Avoid relocation information in final vmlinux 2023-03-20 12:10 [PATCH v5] x86: Avoid relocation information in final vmlinux Petr Pavlu 2023-03-20 18:35 ` Nick Desaulniers @ 2023-03-20 20:12 ` Dave Hansen 2023-03-21 5:23 ` Nathan Chancellor 1 sibling, 1 reply; 7+ messages in thread From: Dave Hansen @ 2023-03-20 20:12 UTC (permalink / raw) To: Petr Pavlu, tglx, mingo, bp, dave.hansen, x86, hpa Cc: nathan, ndesaulniers, trix, corbet, linux-kernel On 3/20/23 05:10, Petr Pavlu wrote: > The issue is then that the collected vmlinux file and hence distribution > packages end up unnecessarily large because of this extra data. The > following is a size comparison of vmlinux v6.0 with and without the > relocation information: > | Configuration | With relocs | Stripped relocs | > | x86_64_defconfig | 70 MB | 43 MB | > | +CONFIG_DEBUG_INFO | 818 MB | 367 MB | > > Optimize a resulting vmlinux by adding a postlink step that splits the > relocation information into vmlinux.relocs and then strips it from the > vmlinux binary. When I saw that this adds a postlink step, I read that as, "adds another step to the unbearably slow single-threaded part of kernel builds". :) But, here's one data point that made me feel a lot better. Using a random .config: > https://sr71.net/~dave/intel/config-reloctest the builds get a _bit_ slower, going from 37.0s->37.7s. This is pretty arbitrary of course, using my compiler on my hardware, so YMMV. But, for me, this seems like a reasonable tradeoff given the space savings. I'd be curious what other people are seeing. ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v5] x86: Avoid relocation information in final vmlinux 2023-03-20 20:12 ` Dave Hansen @ 2023-03-21 5:23 ` Nathan Chancellor 0 siblings, 0 replies; 7+ messages in thread From: Nathan Chancellor @ 2023-03-21 5:23 UTC (permalink / raw) To: Dave Hansen Cc: Petr Pavlu, tglx, mingo, bp, dave.hansen, x86, hpa, ndesaulniers, trix, corbet, linux-kernel On Mon, Mar 20, 2023 at 01:12:07PM -0700, Dave Hansen wrote: > On 3/20/23 05:10, Petr Pavlu wrote: > > The issue is then that the collected vmlinux file and hence distribution > > packages end up unnecessarily large because of this extra data. The > > following is a size comparison of vmlinux v6.0 with and without the > > relocation information: > > | Configuration | With relocs | Stripped relocs | > > | x86_64_defconfig | 70 MB | 43 MB | > > | +CONFIG_DEBUG_INFO | 818 MB | 367 MB | > > > > Optimize a resulting vmlinux by adding a postlink step that splits the > > relocation information into vmlinux.relocs and then strips it from the > > vmlinux binary. > > When I saw that this adds a postlink step, I read that as, "adds another > step to the unbearably slow single-threaded part of kernel builds". :) > > But, here's one data point that made me feel a lot better. Using a > random .config: > > > https://sr71.net/~dave/intel/config-reloctest > > the builds get a _bit_ slower, going from 37.0s->37.7s. This is pretty > arbitrary of course, using my compiler on my hardware, so YMMV. But, > for me, this seems like a reasonable tradeoff given the space savings. > > I'd be curious what other people are seeing. I am seeing a negligible difference (~1%) with LLVM 16 when targeting the following configuration combinations and building the 'bzImage' target. * allmodconfig: Benchmark 1: v6.3-rc3 Time (mean ± σ): 93.370 s ± 0.313 s [User: 3462.570 s, System: 371.420 s] Range (min … max): 92.993 s … 93.659 s 5 runs Benchmark 2: v6.3-rc3 + "x86: Avoid relocation information in final vmlinux" Time (mean ± σ): 93.539 s ± 0.193 s [User: 3464.361 s, System: 370.709 s] Range (min … max): 93.281 s … 93.816 s 5 runs Summary 'v6.3-rc3' ran 1.00 ± 0.00 times faster than 'v6.3-rc3 + "x86: Avoid relocation information in final vmlinux"' * allmodconfig + debug info (DWARF5): Benchmark 1: v6.3-rc3 Time (mean ± σ): 97.952 s ± 0.451 s [User: 3673.380 s, System: 378.814 s] Range (min … max): 97.420 s … 98.568 s 5 runs Benchmark 2: v6.3-rc3 + "x86: Avoid relocation information in final vmlinux" Time (mean ± σ): 98.302 s ± 1.050 s [User: 3674.310 s, System: 378.323 s] Range (min … max): 97.603 s … 100.152 s 5 runs Summary 'v6.3-rc3' ran 1.00 ± 0.01 times faster than 'v6.3-rc3 + "x86: Avoid relocation information in final vmlinux"' * allyesconfig bzImage: Benchmark 1: v6.3-rc3 Time (mean ± σ): 674.232 s ± 1.581 s [User: 24901.883 s, System: 2223.728 s] Range (min … max): 672.478 s … 676.678 s 5 runs Benchmark 2: v6.3-rc3 + "x86: Avoid relocation information in final vmlinux" Time (mean ± σ): 679.783 s ± 2.454 s [User: 24903.720 s, System: 2228.943 s] Range (min … max): 676.369 s … 682.772 s 5 runs Summary 'v6.3-rc3' ran 1.01 ± 0.00 times faster than 'v6.3-rc3 + "x86: Avoid relocation information in final vmlinux"' * allyesconfig + debug info (DWARF5): Benchmark 1: v6.3-rc3 Time (mean ± σ): 709.745 s ± 1.880 s [User: 26570.531 s, System: 2304.563 s] Range (min … max): 707.918 s … 712.818 s 5 runs Benchmark 2: v6.3-rc3 + "x86: Avoid relocation information in final vmlinux" Time (mean ± σ): 711.773 s ± 1.152 s [User: 26571.973 s, System: 2307.176 s] Range (min … max): 710.127 s … 713.224 s 5 runs Summary 'v6.3-rc3' ran 1.00 ± 0.00 times faster than 'v6.3-rc3 + "x86: Avoid relocation information in final vmlinux"' Cheers, Nathan ^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2023-03-24 10:32 UTC | newest] Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2023-03-20 12:10 [PATCH v5] x86: Avoid relocation information in final vmlinux Petr Pavlu 2023-03-20 18:35 ` Nick Desaulniers 2023-03-21 11:57 ` Borislav Petkov 2023-03-24 10:31 ` Petr Pavlu 2023-03-24 10:30 ` Petr Pavlu 2023-03-20 20:12 ` Dave Hansen 2023-03-21 5:23 ` Nathan Chancellor
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