[tip:x86/build] x86, build: Build 16-bit code with -m16 where possible

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Commit-ID:  372cb9eef903d1e18961d2c1a34c75f027f0bd8f
Gitweb:     http://git.kernel.org/tip/372cb9eef903d1e18961d2c1a34c75f027f0bd8f
Author:     David Woodhouse <dwmw2@xxxxxxxxxxxxx>
AuthorDate: Wed, 29 Jan 2014 12:16:47 +0000
Committer:  H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
CommitDate: Wed, 29 Jan 2014 09:47:49 -0800

x86, build: Build 16-bit code with -m16 where possible

Both clang 3.5 and GCC 4.9 will support this (as of r199754 and r207196
respectively). Both have been tested to produce booting kernels when the
16-bit code is built with -m16. (Modulo LLVM PR3997, at least.)

Signed-off-by: David Woodhouse <David.Woodhouse@xxxxxxxxx>
Link: http://lkml.kernel.org/r/1390997807.20153.133.camel@xxxxxxxxxxxxxxxx
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
---
 arch/x86/Makefile | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 9ecbc1c..dbc9b2b 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -13,14 +13,22 @@ endif
 
 # How to compile the 16-bit code.  Note we always compile for -march=i386;
 # that way we can complain to the user if the CPU is insufficient.
-REALMODE_CFLAGS	:= -m32 -g -Os -D__KERNEL__ -DDISABLE_BRANCH_PROFILING \
+#
+# 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))
+M16_CFLAGS	 := -m16
+
+REALMODE_CFLAGS	:= -g -Os -D__KERNEL__ -DDISABLE_BRANCH_PROFILING \
+		   $(call cc-option, $(M16_CFLAGS), $(CODE16GCC_CFLAGS)) \
 		   -Wall -Wstrict-prototypes -march=i386 -mregparm=3 \
-		   -include $(srctree)/arch/x86/boot/code16gcc.h \
 		   -fno-strict-aliasing -fomit-frame-pointer -fno-pic \
 		   -mno-mmx -mno-sse \
 		   $(call cc-option, -ffreestanding) \
-		   $(call cc-option, -fno-toplevel-reorder,\
-		   $(call cc-option, -fno-unit-at-a-time)) \
 		   $(call cc-option, -fno-stack-protector) \
 		   $(call cc-option, -mpreferred-stack-boundary=2)
 export REALMODE_CFLAGS
--
To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html




[Index of Archives]     [Linux Stable Commits]     [Linux Stable Kernel]     [Linux Kernel]     [Linux USB Devel]     [Linux Video &Media]     [Linux Audio Users]     [Yosemite News]     [Linux SCSI]

  Powered by Linux