[PATCH] objtool, compiler.h: Fix __unreachable section relocation size

[Josh Poimboeuf]

Linus reported the following commit broke module loading on his laptop:

  d1091c7fa3d5 ("objtool: Improve detection of BUG() and other dead ends")

It showed errors like the following:

  module: overflow in relocation type 10 val ffffffffc02afc81
  module: 'nvme' likely not compiled with -mcmodel=kernel

The problem is that the __unreachable section addresses are stored using
the '.long' asm directive, which isn't big enough for .text section
relative kernel addresses.  Use relative addresses instead:

  ".long %c0b - .\t\n"

Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Reported-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Fixes: d1091c7fa3d5 ("objtool: Improve detection of BUG() and other dead ends")
Link: 20170301060504.oltm3iws6fmubnom@treble">http://lkml.kernel.org/r/20170301060504.oltm3iws6fmubnom@treble
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 include/linux/compiler-gcc.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index 76e28c229805..b6bb9019d87f 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -201,7 +201,7 @@
 #define annotate_unreachable() ({					\
 	asm("%c0:\t\n"							\
 	    ".pushsection __unreachable, \"a\"\t\n"			\
-	    ".long %c0b\t\n"						\
+	    ".long %c0b - .\t\n"					\
 	    ".popsection\t\n" : : "i" (__LINE__));			\
 })
 #else