[PATCH] x86: Detect CFI support in the assembler at runtime

... instead of using a CONFIG option. The config option still controls
if the resulting executable actually has unwind information.

This is useful to prevent compilation errors when users select
CONFIG_STACK_UNWIND on old binutils and also allows to use
CFI in the future for non kernel debugging applications.

Cc: jbeulich@novell.com
Cc: sam@ravnborg.org
Signed-off-by: Andi Kleen <ak@suse.de>

diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt
index b7d6abb..e2cbd59 100644 (file)
--- a/Documentation/kbuild/makefiles.txt
+++ b/Documentation/kbuild/makefiles.txt
@@ -421,6 +421,11 @@ more details, with real examples.
        The second argument is optional, and if supplied will be used
        if first argument is not supported.
 
        The second argument is optional, and if supplied will be used
        if first argument is not supported.
 

+    as-instr
+       as-instr checks if the assembler reports a specific instruction
+       and then outputs either option1 or option2
+       C escapes are supported in the test instruction
+

     cc-option
        cc-option is used to check if $(CC) supports a given option, and not
        supported to use an optional second option.
     cc-option
        cc-option is used to check if $(CC) supports a given option, and not
        supported to use an optional second option.

diff --git a/arch/i386/Makefile b/arch/i386/Makefile
index 3e4adb1..508cdbe 100644 (file)
--- a/arch/i386/Makefile
+++ b/arch/i386/Makefile
@@ -46,6 +46,10 @@ cflags-y += -ffreestanding
 # a lot more stack due to the lack of sharing of stacklots:
 CFLAGS                         += $(shell if [ $(call cc-version) -lt 0400 ] ; then echo $(call cc-option,-fno-unit-at-a-time); fi ;)
 
 # a lot more stack due to the lack of sharing of stacklots:
 CFLAGS                         += $(shell if [ $(call cc-version) -lt 0400 ] ; then echo $(call cc-option,-fno-unit-at-a-time); fi ;)
 

+# do binutils support CFI?
+cflags-y += $(call as-instr,.cfi_startproc\n.cfi_endproc,-DCONFIG_AS_CFI=1,)
+AFLAGS += $(call as-instr,.cfi_startproc\n.cfi_endproc,-DCONFIG_AS_CFI=1,)
+

 CFLAGS += $(cflags-y)
 
 # Default subarch .c files
 CFLAGS += $(cflags-y)
 
 # Default subarch .c files

diff --git a/arch/x86_64/Makefile b/arch/x86_64/Makefile
index 431bb4b..d6472dd 100644 (file)
--- a/arch/x86_64/Makefile
+++ b/arch/x86_64/Makefile
@@ -54,6 +54,9 @@ endif
 cflags-y += $(call cc-option,-funit-at-a-time)
 # prevent gcc from generating any FP code by mistake
 cflags-y += $(call cc-option,-mno-sse -mno-mmx -mno-sse2 -mno-3dnow,)
 cflags-y += $(call cc-option,-funit-at-a-time)
 # prevent gcc from generating any FP code by mistake
 cflags-y += $(call cc-option,-mno-sse -mno-mmx -mno-sse2 -mno-3dnow,)

+# do binutils support CFI?
+cflags-y += $(call as-instr,.cfi_startproc\n.cfi_endproc,-DCONFIG_AS_CFI=1,)
+AFLAGS += $(call as-instr,.cfi_startproc\n.cfi_endproc,-DCONFIG_AS_CFI=1,)

 
 CFLAGS += $(cflags-y)
 CFLAGS_KERNEL += $(cflags-kernel-y)
 
 CFLAGS += $(cflags-y)
 CFLAGS_KERNEL += $(cflags-kernel-y)

diff --git a/include/asm-x86_64/dwarf2.h b/include/asm-x86_64/dwarf2.h
index 0744db7..2b93683 100644 (file)
--- a/include/asm-x86_64/dwarf2.h
+++ b/include/asm-x86_64/dwarf2.h
@@ -13,7 +13,7 @@
    away for older version. 
  */
 
    away for older version. 
  */
 

-#ifdef CONFIG_UNWIND_INFO
+#ifdef CONFIG_AS_CFI

 
 #define CFI_STARTPROC .cfi_startproc
 #define CFI_ENDPROC .cfi_endproc
 
 #define CFI_STARTPROC .cfi_startproc
 #define CFI_ENDPROC .cfi_endproc

diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index 3d52389..7adef12 100644 (file)
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -63,6 +63,13 @@ as-option = $(shell if $(CC) $(CFLAGS) $(1) -Wa,-Z -c -o /dev/null \
             -xassembler /dev/null > /dev/null 2>&1; then echo "$(1)"; \
             else echo "$(2)"; fi ;)
 
             -xassembler /dev/null > /dev/null 2>&1; then echo "$(1)"; \
             else echo "$(2)"; fi ;)
 

+# as-instr
+# Usage: cflags-y += $(call as-instr, instr, option1, option2)
+
+as-instr = $(shell if echo -e "$(1)" | $(AS) -Z -o astest$$$$.out \
+                  2>&1 >/dev/null ; then echo "$(2)"; else echo "$(3)"; fi; \
+                  rm -f astest$$$$.out)
+

 # cc-option
 # Usage: cflags-y += $(call cc-option, -march=winchip-c6, -march=i586)
 
 # cc-option
 # Usage: cflags-y += $(call cc-option, -march=winchip-c6, -march=i586)