kallsyms: fix segfault in prefix_underscores_count()

Commit b478b782e1 "kallsyms, tracing: output
more proper symbol name" introduces a "bugfix" that introduces a segfault
in kallsyms in my configurations.

The cause is the introduction of prefix_underscores_count() which attempts
to count underscores, even in symbols that do not have them.  As a result,
it just uselessly runs past the end of the buffer until it crashes:

  CC      init/version.o
  LD      init/built-in.o
  LD      .tmp_vmlinux1
  KSYM    .tmp_kallsyms1.S
/bin/sh: line 1: 16934 Done                    sh-linux-gnu-nm -n .tmp_vmlinux1
     16935 Segmentation fault      | scripts/kallsyms > .tmp_kallsyms1.S
make: *** [.tmp_kallsyms1.S] Error 139

This simplifies the logic and just does a straightforward count.

Signed-off-by: Paul Mundt <[email protected]>
Reviewed-by: Li Zefan <[email protected]>
Cc: Lai Jiangshan <[email protected]>
Cc: Sam Ravnborg <[email protected]>
Cc: Paulo Marques <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: <[email protected]>		[2.6.30.x, 2.6.31.x]
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

scripts/kallsyms.c

@@ -585,7 +585,7 @@ static int prefix_underscores_count(const char *str)
 {
 	const char *tail = str;
 
-	while (*tail != '_')
+	while (*tail == '_')
 		tail++;
 
 	return tail - str;