kallsyms: fix absolute addresses for kASLR

Currently symbols that are absolute addresses are incorrectly displayed
in /proc/kallsyms if the kernel is loaded with kASLR.

The problem was that the scripts/kallsyms.c file which generates the
array of symbol names and addresses uses an relocatable value for all
symbols, even absolute symbols.  This patch fixes that.

Several kallsyms output in different boot states for comparison:

  $ egrep '_(stext|_per_cpu_(start|end))' /root/kallsyms.nokaslr
  0000000000000000 D __per_cpu_start
  0000000000014280 D __per_cpu_end
  ffffffff810001c8 T _stext
  $ egrep '_(stext|_per_cpu_(start|end))' /root/kallsyms.kaslr1
  000000001f200000 D __per_cpu_start
  000000001f214280 D __per_cpu_end
  ffffffffa02001c8 T _stext
  $ egrep '_(stext|_per_cpu_(start|end))' /root/kallsyms.kaslr2
  000000000d400000 D __per_cpu_start
  000000000d414280 D __per_cpu_end
  ffffffff8e4001c8 T _stext
  $ egrep '_(stext|_per_cpu_(start|end))' /root/kallsyms.kaslr-fixed
  0000000000000000 D __per_cpu_start
  0000000000014280 D __per_cpu_end
  ffffffffadc001c8 T _stext
Signed-off-by: NAndy Honig <ahonig@google.com>
Signed-off-by: NKees Cook <keescook@chromium.org>
Cc: Michal Marek <mmarek@suse.cz>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

scripts/kallsyms.c

@@ -330,8 +330,7 @@ static void write_src(void)
 				printf("\tPTR\t_text + %#llx\n",
 					table[i].addr - _text);
 			else
-				printf("\tPTR\t_text - %#llx\n",
-					_text - table[i].addr);
+				printf("\tPTR\t%#llx\n", table[i].addr);
 		} else {
 			printf("\tPTR\t%#llx\n", table[i].addr);
 		}