Messages in this thread Patch in this message | | | From | George Rimar <> | Subject | Re: [PATCH v3] x86_64: Add "-m elf_i386" when linking i386 object files. | Date | Sat, 12 Jan 2019 10:00:36 +0000 |
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Signed-off-by: George Rimar <grimar@accesssoftek.com>
Best regards, George | Developer | Access Softek, Inc
________________________________________ От: Tri Vo <trong@android.com> Отправлено: 11 января 2019 г. 23:10 Кому: x86@kernel.org; tglx@linutronix.de; mingo@redhat.com; bp@alien8.de; hpa@zytor.com Копия: George Rimar; dima@golovin.in; morbo@google.com; ndesaulniers@google.com; matz@suse.de; ruiu@google.com; linux-kernel@vger.kernel.org; Tri Vo Тема: [PATCH v3] x86_64: Add "-m elf_i386" when linking i386 object files.
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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.
"man ld" doesn't explicitly state any tie-breakers between -m and OUTPUT_FORMAT. BFD and Gold linkers override -m value with OUTPUT_FORMAT. But LLVM lld has a different behavior. When supplied with contradicting -m and OUTPUT_FORMAT values it fails with the following error message:
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
This is not a functional change for GNU ld, because (although not explicitly documented) it already overrides -m EMULATION with OUTPUT_FORMAT.
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: George Rimar <grimar@accesssoftek.com> Signed-off-by: Tri Vo <trong@android.com> Tested-by: Tri Vo <trong@android.com> Tested-by: Nick Desaulniers <ndesaulniers@google.com> --- v2: updated commit message to clarify that ld documentation is ambiguous w.r.t -m vs OUTPUT_FORMAT behavior. v3: fixed/added SOB and "Tested-by" fields.
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 -- 2.20.1.97.g81188d93c3-goog
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