diff options
| author | H. Peter Anvin <hpa@linux.intel.com> | 2014-06-04 13:16:48 -0700 |
|---|---|---|
| committer | H. Peter Anvin <hpa@linux.intel.com> | 2014-06-04 13:16:48 -0700 |
| commit | a9cfccee6604854aebc70215610b9788667f4fec (patch) | |
| tree | fd5386d1e9c8d43eb1a52da94b57382b7a509ee0 /arch | |
| parent | a9358bc3531901a15e2f7cd48550c9555fc0288f (diff) | |
x86, build: Change code16gcc.h from a C header to an assembly header
By changing code16gcc.h from a C header to an assembly header and use
the -Wa,... option to gcc to force it to be added to the assembly
input, we can avoid the problems with gcc reordering code bits on us.
If we have -m16, we still use it, of course.
Suggested-by: Kevin O'Connor <kevin@koconnor.net>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/n/tip-xw8ibgdemucl9fz3i1bymu6w@git.kernel.org
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/Makefile | 9 | ||||
| -rw-r--r-- | arch/x86/boot/code16gcc.h | 24 |
2 files changed, 13 insertions, 20 deletions
diff --git a/arch/x86/Makefile b/arch/x86/Makefile index 602f57e590b5..a98cc9064d8b 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -15,12 +15,9 @@ endif # that way we can complain to the user if the CPU is insufficient. # # The -m16 option is supported by GCC >= 4.9 and clang >= 3.5. For -# older versions of GCC, we need to play evil and unreliable tricks to -# attempt to ensure that our asm(".code16gcc") is first in the asm -# output. -CODE16GCC_CFLAGS := -m32 -include $(srctree)/arch/x86/boot/code16gcc.h \ - $(call cc-option, -fno-toplevel-reorder,\ - $(call cc-option, -fno-unit-at-a-time)) +# older versions of GCC, include an *assembly* header to make sure that +# gcc doesn't play any games behind our back. +CODE16GCC_CFLAGS := -m32 -Wa,$(srctree)/arch/x86/boot/code16gcc.h M16_CFLAGS := $(call cc-option, -m16, $(CODE16GCC_CFLAGS)) REALMODE_CFLAGS := $(M16_CFLAGS) -g -Os -D__KERNEL__ \ diff --git a/arch/x86/boot/code16gcc.h b/arch/x86/boot/code16gcc.h index d93e48010b61..5ff426535397 100644 --- a/arch/x86/boot/code16gcc.h +++ b/arch/x86/boot/code16gcc.h @@ -1,15 +1,11 @@ -/* - * code16gcc.h - * - * This file is -include'd when compiling 16-bit C code. - * Note: this asm() needs to be emitted before gcc emits any code. - * Depending on gcc version, this requires -fno-unit-at-a-time or - * -fno-toplevel-reorder. - * - * Hopefully gcc will eventually have a real -m16 option so we can - * drop this hack long term. - */ +# +# code16gcc.h +# +# This file is added to the assembler via -Wa when compiling 16-bit C code. +# This is done this way instead via asm() to make sure gcc does not reorder +# things around us. +# +# gcc 4.9+ has a real -m16 option so we can drop this hack long term. +# -#ifndef __ASSEMBLY__ -asm(".code16gcc"); -#endif + .code16gcc |