On Mon, Oct 12, 2020 at 2:11 PM 'Nick Desaulniers' via Clang Built Linux <[email protected]> wrote: > > On Mon, Sep 28, 2020 at 3:49 PM Nathan Chancellor > <[email protected]> wrote: > > > > After turning on warnings for orphan section placement, enabling > > CONFIG_UNWINDER_FRAME_POINTER instead of CONFIG_UNWINDER_ARM causes > > thousands of warnings when clang + ld.lld are used: > > > > $ scripts/config --file arch/arm/configs/multi_v7_defconfig \ > > -d CONFIG_UNWINDER_ARM \ > > -e CONFIG_UNWINDER_FRAME_POINTER > > $ make -skj"$(nproc)" ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- LLVM=1 > > defconfig zImage > > ld.lld: warning: init/built-in.a(main.o):(.ARM.extab) is being placed in > > '.ARM.extab' > > ld.lld: warning: init/built-in.a(main.o):(.ARM.extab.init.text) is being > > placed in '.ARM.extab.init.text' > > ld.lld: warning: init/built-in.a(main.o):(.ARM.extab.ref.text) is being > > placed in '.ARM.extab.ref.text' > > ld.lld: warning: init/built-in.a(do_mounts.o):(.ARM.extab.init.text) is > > being placed in '.ARM.extab.init.text' > > ld.lld: warning: init/built-in.a(do_mounts.o):(.ARM.extab) is being placed > > in '.ARM.extab' > > ld.lld: warning: init/built-in.a(do_mounts_rd.o):(.ARM.extab.init.text) is > > being placed in '.ARM.extab.init.text' > > ld.lld: warning: init/built-in.a(do_mounts_rd.o):(.ARM.extab) is being > > placed in '.ARM.extab' > > ld.lld: warning: init/built-in.a(do_mounts_initrd.o):(.ARM.extab.init.text) > > is being placed in '.ARM.extab.init.text' > > ld.lld: warning: init/built-in.a(initramfs.o):(.ARM.extab.init.text) is > > being placed in '.ARM.extab.init.text' > > ld.lld: warning: init/built-in.a(initramfs.o):(.ARM.extab) is being placed > > in '.ARM.extab' > > ld.lld: warning: init/built-in.a(calibrate.o):(.ARM.extab.init.text) is > > being placed in '.ARM.extab.init.text' > > ld.lld: warning: init/built-in.a(calibrate.o):(.ARM.extab) is being placed > > in '.ARM.extab' > > > > These sections are handled by the ARM_UNWIND_SECTIONS define, which is > > only added to the list of sections when CONFIG_ARM_UNWIND is set. > > CONFIG_ARM_UNWIND is a hidden symbol that is only selected when > > CONFIG_UNWINDER_ARM is set so CONFIG_UNWINDER_FRAME_POINTER never > > handles these sections. According to the help text of > > CONFIG_UNWINDER_ARM, these sections should be discarded so that the > > kernel image size is not affected. > > My apologies for taking so long to review this. > > I have a suspicion that these come from forcing on configs that > Kconfig/menuconfig would block, and aren't clang or lld specific, yet > are exposed by the new linker warnings for orphan section placement > (good). That said, we definitely have OEMs in Android land that still > prefer the older unwinder. > > From https://developer.arm.com/documentation/ihi0038/b/ (click > download in top left), section 4.4.1 "Sections" has a note: > > ``` > Tables are not required for ABI compliance at the C/Assembler level > but are required for C++. > ``` > > Review-by: Nick Desaulniers <[email protected]> > Tested-by: Nick Desaulniers <[email protected]> > > Please submit to: > https://www.arm.linux.org.uk/developer/patches/add.php > > > > > Fixes: 5a17850e251a ("arm/build: Warn on orphan section placement") > > Link: https://github.com/ClangBuiltLinux/linux/issues/1152 > > Reported-by: kernel test robot <[email protected]> > > Signed-off-by: Nathan Chancellor <[email protected]> > > --- > > arch/arm/kernel/vmlinux.lds.S | 4 ++++ > > 1 file changed, 4 insertions(+) > > > > diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S > > index 5f4922e858d0..a2c0d96b0580 100644 > > --- a/arch/arm/kernel/vmlinux.lds.S > > +++ b/arch/arm/kernel/vmlinux.lds.S > > @@ -40,6 +40,10 @@ SECTIONS > > ARM_DISCARD > > #ifndef CONFIG_SMP_ON_UP > > *(.alt.smp.init) > > +#endif > > +#ifndef CONFIG_ARM_UNWIND > > + *(.ARM.exidx*) > > I don't think we need the wildcard, as without this line, I see: > > ld.lld: warning: <internal>:(.ARM.exidx) is being placed in '.ARM.exidx'
We may need the wildcard if there are -ffunction-sections builds. In clang, .ARM.exidx* cannot be removed even with -fno-unwind-tables -fno-exceptions. > though I do see binutils linker scripts use precisely what you have. > So I guess that's fine. > > I guess we can't reuse `ARM_UNWIND_SECTIONS` since the ALIGN and > linker-script-defined-symbols would be weird in a DISCARD clause? > > > > + *(.ARM.extab*) > > #endif > > } > > > > > > base-commit: 6e0bf0e0e55000742a53c5f3b58f8669e0091a11 > > -- > > > -- > Thanks, > ~Nick Desaulniers > > -- > You received this message because you are subscribed to the Google Groups > "Clang Built Linux" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/clang-built-linux/CAKwvOd%3D%2B98r6F4JjrPEoWX88WQ%3DB-KMRP2eWojabLk6it3i5KA%40mail.gmail.com. -- 宋方睿
