Messages in this thread | | | From | Tri Vo <> | Date | Wed, 12 Dec 2018 11:48:51 -0800 | Subject | Re: [RFC PATCH] x86_64: Add "-m elf_i386" when linking i386 object files. |
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Adding appropriate people, lists. On Tue, Dec 11, 2018 at 1:07 PM Nick Desaulniers <ndesaulniers@google.com> wrote: > > On Mon, Dec 10, 2018 at 2:50 PM Nick Desaulniers > <ndesaulniers@google.com> wrote: > > > > On Mon, Dec 10, 2018 at 2:26 PM Tri Vo <trong@android.com> wrote: > > > > > > From: George Rimar <grimar@accesssoftek.com> > > > > > > Linux kernel uses OUTPUT_FORMAT in it's linker scripts. Most of the time > > > -m option is passed to the linker with correct architecture, but > > > sometimes (at least for x86_64) the -m option contradicts OUTPUT_FORMAT > > > directive. Specifically, arch/x86/boot and arch/x86/realmode/rm modules > > > have i386 object files, but are linked with -m elf_x86_64 linker flag > > > when building for x86_64. > > > > > > BFD and Gold linkers are OK with this, but lld fails: > > > ld.lld: error: arch/x86/realmode/rm/header.o is incompatible with elf_x86_64 > > > > > > Suggested fix: just add correct -m after incorrect one (it overrides > > > it), so the linker invocation looks like this: ld -m elf_x86_64 -z > > > max-page-size=0x200000 -m elf_i386 --emit-relocs -T realmode.lds > > > header.o trampoline_64.o stack.o reboot.o -o realmode.elf (it will also > > > work with GNU ld, because it supports OUTPUT_FORMAT and just ignores -m > > > options if this directive is in the linker script). > > > > > > Tested by building x86_64 kernel with GNU gcc/ld toolchain and booting > > > it in QEMU. > > > > > > Suggested-by: Dmitry Golovin <dima@golovin.in> > > > Signed-off-by: Tri Vo <trong@android.com> > > > Tested-by: Tri Vo <trong@android.com> > > > > This fixes the following linkage error I observe when linking an x86 > > kernel with LLD: > > > > ``` > > LD arch/x86/realmode/rm/realmode.elf > > ld.lld: error: arch/x86/realmode/rm/header.o is incompatible with elf_x86_64 > > ld.lld: error: arch/x86/realmode/rm/trampoline_64.o is incompatible > > with elf_x86_64 > > ld.lld: error: arch/x86/realmode/rm/stack.o is incompatible with elf_x86_64 > > ld.lld: error: arch/x86/realmode/rm/reboot.o is incompatible with elf_x86_64 > > ld.lld: error: arch/x86/realmode/rm/wakeup_asm.o is incompatible with elf_x86_64 > > ld.lld: error: arch/x86/realmode/rm/wakemain.o is incompatible with elf_x86_64 > > ld.lld: error: arch/x86/realmode/rm/video-mode.o is incompatible with elf_x86_64 > > ld.lld: error: arch/x86/realmode/rm/copy.o is incompatible with elf_x86_64 > > ld.lld: error: arch/x86/realmode/rm/bioscall.o is incompatible with elf_x86_64 > > ld.lld: error: arch/x86/realmode/rm/regs.o is incompatible with elf_x86_64 > > ld.lld: error: arch/x86/realmode/rm/video-vga.o is incompatible with elf_x86_64 > > ld.lld: error: arch/x86/realmode/rm/video-vesa.o is incompatible with elf_x86_64 > > ld.lld: error: arch/x86/realmode/rm/video-bios.o is incompatible with elf_x86_64 > > arch/x86/realmode/rm/Makefile:55: recipe for target > > 'arch/x86/realmode/rm/realmode.elf' failed > > ``` > > Tested-by: Nick Desaulniers <ndesaulniers@google.com> > > > > Looks like we still have a few other (unrelated) issues to track down > > with LLD, but this gets us one step closer. > > > > Thanks for sending this, Tri! > > Just some additional thoughts on this: > > The kernel is adding -m elf_x86_64 to the linker command line > parameters, but then relying on binutils tie-breaking-behavior by > specifying a different architecture via linker script. So it's > ambiguous which arch the kernel is trying to link for, and the kernel > gets lucky/relies on the way ld.bfd happens to resolve this ambiguity > without warning. An alternative fix may be to just filter out/remove > the -m elf_x86_64 for this target's linker flags. > > > > > > --- > > > arch/x86/boot/Makefile | 2 +- > > > arch/x86/realmode/rm/Makefile | 2 +- > > > 2 files changed, 2 insertions(+), 2 deletions(-) > > > > > > diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile > > > index 9b5adae9cc40..e2839b5c246c 100644 > > > --- a/arch/x86/boot/Makefile > > > +++ b/arch/x86/boot/Makefile > > > @@ -100,7 +100,7 @@ $(obj)/zoffset.h: $(obj)/compressed/vmlinux FORCE > > > AFLAGS_header.o += -I$(objtree)/$(obj) > > > $(obj)/header.o: $(obj)/zoffset.h > > > > > > -LDFLAGS_setup.elf := -T > > > +LDFLAGS_setup.elf := -m elf_i386 -T > > > $(obj)/setup.elf: $(src)/setup.ld $(SETUP_OBJS) FORCE > > > $(call if_changed,ld) > > > > > > diff --git a/arch/x86/realmode/rm/Makefile b/arch/x86/realmode/rm/Makefile > > > index 4463fa72db94..96cb20de08af 100644 > > > --- a/arch/x86/realmode/rm/Makefile > > > +++ b/arch/x86/realmode/rm/Makefile > > > @@ -47,7 +47,7 @@ $(obj)/pasyms.h: $(REALMODE_OBJS) FORCE > > > targets += realmode.lds > > > $(obj)/realmode.lds: $(obj)/pasyms.h > > > > > > -LDFLAGS_realmode.elf := --emit-relocs -T > > > +LDFLAGS_realmode.elf := -m elf_i386 --emit-relocs -T > > > CPPFLAGS_realmode.lds += -P -C -I$(objtree)/$(obj) > > > > > > targets += realmode.elf > > > -- > > > 2.20.0.rc2.403.gdbc3b29805-goog > > > > > > > > > -- > > Thanks, > > ~Nick Desaulniers > > > > -- > Thanks, > ~Nick Desaulniers
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