x86/alternatives: Add an auxilary section

Add .altinstr_aux for additional instructions which will be used
before and/or during patching. All stuff which needs more
sophisticated patching should go there. See next patch.

Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1453842730-28463-8-git-send-email-bp@alien8.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 74e4bf1..92dc211 100644 (file)
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -195,6 +195,17 @@ SECTIONS
        :init
 #endif
 
+       /*
+        * Section for code used exclusively before alternatives are run. All
+        * references to such code must be patched out by alternatives, normally
+        * by using X86_FEATURE_ALWAYS CPU feature bit.
+        *
+        * See static_cpu_has() for an example.
+        */
+       .altinstr_aux : AT(ADDR(.altinstr_aux) - LOAD_OFFSET) {
+               *(.altinstr_aux)
+       }
+
        INIT_DATA_SECTION(16)
 
        .x86_cpu_dev.init : AT(ADDR(.x86_cpu_dev.init) - LOAD_OFFSET) {