| Message ID | 20200903203053.3411268-14-samitolvanen@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Add support for Clang LTO | expand |
On Thu, Sep 03, 2020 at 01:30:38PM -0700, Sami Tolvanen wrote: > LLD always splits sections with LTO, which increases module sizes. This > change adds a linker script that merges the split sections in the final > module. > > Suggested-by: Nick Desaulniers <ndesaulniers@google.com> > Signed-off-by: Sami Tolvanen <samitolvanen@google.com> We'll likely need to come back around to this for FGKASLR (to keep the .text.* sections separated), but that's no different than the existing concerns for FGKASLR on the main kernel. Reviewed-by: Kees Cook <keescook@chromium.org>
On Fri, Sep 4, 2020 at 5:31 AM Sami Tolvanen <samitolvanen@google.com> wrote: > > LLD always splits sections with LTO, which increases module sizes. This > change adds a linker script that merges the split sections in the final > module. > > Suggested-by: Nick Desaulniers <ndesaulniers@google.com> > Signed-off-by: Sami Tolvanen <samitolvanen@google.com> > --- > Makefile | 2 ++ > scripts/module-lto.lds | 26 ++++++++++++++++++++++++++ > 2 files changed, 28 insertions(+) > create mode 100644 scripts/module-lto.lds > > diff --git a/Makefile b/Makefile > index c69e07bd506a..bb82a4323f1d 100644 > --- a/Makefile > +++ b/Makefile > @@ -921,6 +921,8 @@ CC_FLAGS_LTO_CLANG += -fvisibility=default > # Limit inlining across translation units to reduce binary size > LD_FLAGS_LTO_CLANG := -mllvm -import-instr-limit=5 > KBUILD_LDFLAGS += $(LD_FLAGS_LTO_CLANG) > + > +KBUILD_LDS_MODULE += $(srctree)/scripts/module-lto.lds > endif > > ifdef CONFIG_LTO > diff --git a/scripts/module-lto.lds b/scripts/module-lto.lds > new file mode 100644 > index 000000000000..cbb11dc3639a > --- /dev/null > +++ b/scripts/module-lto.lds > @@ -0,0 +1,26 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +/* > + * With CONFIG_LTO_CLANG, LLD always enables -fdata-sections and > + * -ffunction-sections, which increases the size of the final module. > + * Merge the split sections in the final binary. > + */ > +SECTIONS { > + __patchable_function_entries : { *(__patchable_function_entries) } > + > + .bss : { > + *(.bss .bss.[0-9a-zA-Z_]*) > + *(.bss..L*) > + } > + > + .data : { > + *(.data .data.[0-9a-zA-Z_]*) > + *(.data..L*) > + } > + > + .rodata : { > + *(.rodata .rodata.[0-9a-zA-Z_]*) > + *(.rodata..L*) > + } > + > + .text : { *(.text .text.[0-9a-zA-Z_]*) } > +} > -- > 2.28.0.402.g5ffc5be6b7-goog > After I apply https://patchwork.kernel.org/patch/11757323/, is it possible to do like this ? #ifdef CONFIG_LTO SECTIONS { ... }; #endif in scripts/module.lds.S
On Tue, Sep 08, 2020 at 12:25:54AM +0900, Masahiro Yamada wrote: > On Fri, Sep 4, 2020 at 5:31 AM Sami Tolvanen <samitolvanen@google.com> wrote: > > > > LLD always splits sections with LTO, which increases module sizes. This > > change adds a linker script that merges the split sections in the final > > module. > > > > Suggested-by: Nick Desaulniers <ndesaulniers@google.com> > > Signed-off-by: Sami Tolvanen <samitolvanen@google.com> > > --- > > Makefile | 2 ++ > > scripts/module-lto.lds | 26 ++++++++++++++++++++++++++ > > 2 files changed, 28 insertions(+) > > create mode 100644 scripts/module-lto.lds > > > > diff --git a/Makefile b/Makefile > > index c69e07bd506a..bb82a4323f1d 100644 > > --- a/Makefile > > +++ b/Makefile > > @@ -921,6 +921,8 @@ CC_FLAGS_LTO_CLANG += -fvisibility=default > > # Limit inlining across translation units to reduce binary size > > LD_FLAGS_LTO_CLANG := -mllvm -import-instr-limit=5 > > KBUILD_LDFLAGS += $(LD_FLAGS_LTO_CLANG) > > + > > +KBUILD_LDS_MODULE += $(srctree)/scripts/module-lto.lds > > endif > > > > ifdef CONFIG_LTO > > diff --git a/scripts/module-lto.lds b/scripts/module-lto.lds > > new file mode 100644 > > index 000000000000..cbb11dc3639a > > --- /dev/null > > +++ b/scripts/module-lto.lds > > @@ -0,0 +1,26 @@ > > +/* SPDX-License-Identifier: GPL-2.0 */ > > +/* > > + * With CONFIG_LTO_CLANG, LLD always enables -fdata-sections and > > + * -ffunction-sections, which increases the size of the final module. > > + * Merge the split sections in the final binary. > > + */ > > +SECTIONS { > > + __patchable_function_entries : { *(__patchable_function_entries) } > > + > > + .bss : { > > + *(.bss .bss.[0-9a-zA-Z_]*) > > + *(.bss..L*) > > + } > > + > > + .data : { > > + *(.data .data.[0-9a-zA-Z_]*) > > + *(.data..L*) > > + } > > + > > + .rodata : { > > + *(.rodata .rodata.[0-9a-zA-Z_]*) > > + *(.rodata..L*) > > + } > > + > > + .text : { *(.text .text.[0-9a-zA-Z_]*) } > > +} > > -- > > 2.28.0.402.g5ffc5be6b7-goog > > > > > After I apply https://patchwork.kernel.org/patch/11757323/, > is it possible to do like this ? > > > #ifdef CONFIG_LTO > SECTIONS { > ... > }; > #endif > > in scripts/module.lds.S Yes, that should work. I'll change this in v3 after your change is applied. Sami
diff --git a/Makefile b/Makefile index c69e07bd506a..bb82a4323f1d 100644 --- a/Makefile +++ b/Makefile @@ -921,6 +921,8 @@ CC_FLAGS_LTO_CLANG += -fvisibility=default # Limit inlining across translation units to reduce binary size LD_FLAGS_LTO_CLANG := -mllvm -import-instr-limit=5 KBUILD_LDFLAGS += $(LD_FLAGS_LTO_CLANG) + +KBUILD_LDS_MODULE += $(srctree)/scripts/module-lto.lds endif ifdef CONFIG_LTO diff --git a/scripts/module-lto.lds b/scripts/module-lto.lds new file mode 100644 index 000000000000..cbb11dc3639a --- /dev/null +++ b/scripts/module-lto.lds @@ -0,0 +1,26 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * With CONFIG_LTO_CLANG, LLD always enables -fdata-sections and + * -ffunction-sections, which increases the size of the final module. + * Merge the split sections in the final binary. + */ +SECTIONS { + __patchable_function_entries : { *(__patchable_function_entries) } + + .bss : { + *(.bss .bss.[0-9a-zA-Z_]*) + *(.bss..L*) + } + + .data : { + *(.data .data.[0-9a-zA-Z_]*) + *(.data..L*) + } + + .rodata : { + *(.rodata .rodata.[0-9a-zA-Z_]*) + *(.rodata..L*) + } + + .text : { *(.text .text.[0-9a-zA-Z_]*) } +}
LLD always splits sections with LTO, which increases module sizes. This change adds a linker script that merges the split sections in the final module. Suggested-by: Nick Desaulniers <ndesaulniers@google.com> Signed-off-by: Sami Tolvanen <samitolvanen@google.com> --- Makefile | 2 ++ scripts/module-lto.lds | 26 ++++++++++++++++++++++++++ 2 files changed, 28 insertions(+) create mode 100644 scripts/module-lto.lds