queue-4.19/x86-build-specify-elf_i386-linker-emulation-explicit.patch

   1 From a1d59c78c333fb83b2a3089a35fa518a5d9dd24e Mon Sep 17 00:00:00 2001
   2 From: George Rimar <grimar@accesssoftek.com>
   3 Date: Fri, 11 Jan 2019 12:10:12 -0800
   4 Subject: x86/build: Specify elf_i386 linker emulation explicitly for i386
   5  objects
   6
   7 [ Upstream commit 927185c124d62a9a4d35878d7f6d432a166b74e3 ]
   8
   9 The kernel uses the OUTPUT_FORMAT linker script command in it's linker
  10 scripts. Most of the time, the -m option is passed to the linker with
  11 correct architecture, but sometimes (at least for x86_64) the -m option
  12 contradicts the OUTPUT_FORMAT directive.
  13
  14 Specifically, arch/x86/boot and arch/x86/realmode/rm produce i386 object
  15 files, but are linked with the -m elf_x86_64 linker flag when building
  16 for x86_64.
  17
  18 The GNU linker manpage doesn't explicitly state any tie-breakers between
  19 -m and OUTPUT_FORMAT. But with BFD and Gold linkers, OUTPUT_FORMAT
  20 overrides the emulation value specified with the -m option.
  21
  22 LLVM lld has a different behavior, however. When supplied with
  23 contradicting -m and OUTPUT_FORMAT values it fails with the following
  24 error message:
  25
  26   ld.lld: error: arch/x86/realmode/rm/header.o is incompatible with elf_x86_64
  27
  28 Therefore, just add the correct -m after the incorrect one (it overrides
  29 it), so the linker invocation looks like this:
  30
  31   ld -m elf_x86_64 -z max-page-size=0x200000 -m elf_i386 --emit-relocs -T \
  32     realmode.lds header.o trampoline_64.o stack.o reboot.o -o realmode.elf
  33
  34 This is not a functional change for GNU ld, because (although not
  35 explicitly documented) OUTPUT_FORMAT overrides -m EMULATION.
  36
  37 Tested by building x86_64 kernel with GNU gcc/ld toolchain and booting
  38 it in QEMU.
  39
  40  [ bp: massage and clarify text. ]
  41
  42 Suggested-by: Dmitry Golovin <dima@golovin.in>
  43 Signed-off-by: George Rimar <grimar@accesssoftek.com>
  44 Signed-off-by: Tri Vo <trong@android.com>
  45 Signed-off-by: Borislav Petkov <bp@suse.de>
  46 Tested-by: Tri Vo <trong@android.com>
  47 Tested-by: Nick Desaulniers <ndesaulniers@google.com>
  48 Cc: "H. Peter Anvin" <hpa@zytor.com>
  49 Cc: Ingo Molnar <mingo@redhat.com>
  50 Cc: Michael Matz <matz@suse.de>
  51 Cc: Thomas Gleixner <tglx@linutronix.de>
  52 Cc: morbo@google.com
  53 Cc: ndesaulniers@google.com
  54 Cc: ruiu@google.com
  55 Cc: x86-ml <x86@kernel.org>
  56 Link: https://lkml.kernel.org/r/20190111201012.71210-1-trong@android.com
  57 Signed-off-by: Sasha Levin <sashal@kernel.org>
  58 ---
  59  arch/x86/boot/Makefile        | 2 +-
  60  arch/x86/realmode/rm/Makefile | 2 +-
  61  2 files changed, 2 insertions(+), 2 deletions(-)
  62
  63 diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
  64 index 9b5adae9cc40..e2839b5c246c 100644
  65 --- a/arch/x86/boot/Makefile
  66 +++ b/arch/x86/boot/Makefile
  67 @@ -100,7 +100,7 @@ $(obj)/zoffset.h: $(obj)/compressed/vmlinux FORCE
  68  AFLAGS_header.o += -I$(objtree)/$(obj)
  69  $(obj)/header.o: $(obj)/zoffset.h
  70
  71 -LDFLAGS_setup.elf      := -T
  72 +LDFLAGS_setup.elf      := -m elf_i386 -T
  73  $(obj)/setup.elf: $(src)/setup.ld $(SETUP_OBJS) FORCE
  74         $(call if_changed,ld)
  75
  76 diff --git a/arch/x86/realmode/rm/Makefile b/arch/x86/realmode/rm/Makefile
  77 index 4463fa72db94..96cb20de08af 100644
  78 --- a/arch/x86/realmode/rm/Makefile
  79 +++ b/arch/x86/realmode/rm/Makefile
  80 @@ -47,7 +47,7 @@ $(obj)/pasyms.h: $(REALMODE_OBJS) FORCE
  81  targets += realmode.lds
  82  $(obj)/realmode.lds: $(obj)/pasyms.h
  83
  84 -LDFLAGS_realmode.elf := --emit-relocs -T
  85 +LDFLAGS_realmode.elf := -m elf_i386 --emit-relocs -T
  86  CPPFLAGS_realmode.lds += -P -C -I$(objtree)/$(obj)
  87
  88  targets += realmode.elf
  89 --
  90 2.19.1
  91