Signed-off-by: George Rimar <gri...@accesssoftek.com>
Best regards,
George | Developer | Access Softek, Inc
________________________________________
От: Tri Vo <tr...@android.com>
Отправлено: 11 января 2019 г. 23:10
Кому: x...@kernel.org; t...@linutronix.de; mi...@redhat.com; b...@alien8.de;
h...@zytor.com
Копия: George Rimar; d...@golovin.in; mo...@google.com;
ndesaulni...@google.com; m...@suse.de; r...@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 <gri...@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 <d...@golovin.in>
Signed-off-by: George Rimar <gri...@accesssoftek.com>
Signed-off-by: Tri Vo <tr...@android.com>
Tested-by: Tri Vo <tr...@android.com>
Tested-by: Nick Desaulniers <ndesaulni...@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
