[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>

1 files changed, 5 insertions, 0 deletions

diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt
index b7d6abb501a6..e2cbd59cf2d0 100644
--- 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.
 
+    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.