On Wed, May 20, 2020 at 10:34:25AM -0700, Fangrui Song wrote: > On 2020-05-20, Ard Biesheuvel wrote: > >On Wed, 20 May 2020 at 17:53, Arvind Sankar <nivedita(a)alum.mit.edu&gt; wrote: > >> > >> On Wed, May 20, 2020 at 10:28:13AM +0800, kbuild test robot wrote: > >> > tree: https://git.kernel.org/pub/scm/linux/kernel/git/efi/efi.git next > >> > head: e5fbadd1179cdadeaa44d71a9ec068c5bc100524 > >> > commit: ce5e3f909fc0ed67e58367b9c56a54c20a51080b [22/40] efi/printf: Add 64-bit and 8-bit integer support > >> > config: x86_64-defconfig (attached as .config) > >> > compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project 135b877874fae96b4372c8a3fbfaa8ff44ff86e3) > >> > reproduce: > >> > wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross > >> > chmod +x ~/bin/make.cross > >> > # install x86_64 cross compiling tool for clang build > >> > # apt-get install binutils-x86-64-linux-gnu > >> > git checkout ce5e3f909fc0ed67e58367b9c56a54c20a51080b > >> > # save the attached .config to linux build tree > >> > COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=x86_64 > >> > > >> > If you fix the issue, kindly add following tag as appropriate > >> > Reported-by: kbuild test robot <lkp(a)intel.com&gt; > >> > > >> > All warnings (new ones prefixed by >>, old ones prefixed by <<): > >> > > >> > >> ld.lld: warning: vsprintf.c:(.discard.unreachable+0x0): has non-ABS relocation R_X86_64_PC32 against symbol '' > >> > > >> > --- > >> > 0-DAY CI Kernel Test Service, Intel Corporation > >> > https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org > >> > >> Clang folk, is anything actually wrong here? This seems to result from > >> use of unreachable() annotation, which generates these > >> .discard.unreachable sections apparently to help objtool. > >> > > > >This came up before, and IIRC, it has already been fixed, only this > >branch is based on v5.7-rc2. > > LLD reports the diagnostic because a PC-relative relocation referencing a > SHF_ALLOC section from a non-SHF_ALLOC section (.discard.unreachable) cannot be > reasonably represented. A non-SHF_ALLOC section is not part of the memory image, thus conceptually > the distance between a non-SHF_ALLOC and a SHF_ALLOC is not a constant which can be resolved at linktime. > This is actually a nice diagnostic which has caught a number of issues. > > % readelf -Wr drivers/firmware/efi/libstub/vsprintf.stub.o > .. > Relocation section '.rela.discard.unreachable' at offset 0xe38 contains 1 entry: > Offset Info Type Symbol's Value Symbol's Name + Addend > 0000000000000000 0000000600000002 R_X86_64_PC32 0000000000000000 .text + ac0 > > --- > > The linker command line is: > > % ld.lld -m elf_x86_64 -T arch/x86/boot/compressed/vmlinux.lds arch/x86/boot/compressed/kernel_info.o arch/x86/boot/compressed/head_64.o arch/x86/boot/compressed/misc.o arch/x86/boot/compressed/string.o arch/x86/boot/compressed/cmdline.o arch/x86/boot/compressed/error.o arch/x86/boot/compressed/piggy.o arch/x86/boot/compressed/cpuflags.o arch/x86/boot/compressed/early_serial_console.o arch/x86/boot/compressed/kaslr.o arch/x86/boot/compressed/kaslr_64.o arch/x86/boot/compressed/mem_encrypt.o arch/x86/boot/compressed/pgtable_64.o arch/x86/boot/compressed/acpi.o drivers/firmware/efi/libstub/lib.a arch/x86/boot/compressed/efi_thunk_64.o -o arch/x86/boot/compressed/vmlinux > ld.lld: warning: vsprintf.c:(.discard.unreachable+0x0): has non-ABS relocation R_X86_64_PC32 against symbol '' > > arch/x86/boot/compressed/vmlinux has an output section .discard.unreachable , which is likely desired. You mean /not/ desired, right?

> > Note that arch/x86/kernel/vmlinux.lds.S has an output section description /DISCARD/ : { ... *(.discard.*) ... }, > but arch/x86/boot/compressed/vmlinux doesn't. > > We can let arch/x86/boot/compressed/vmlinux reuse the /DISCARD/ to fix the issue. Yep.