objtool: Fix another switch table detection issue

Continue the switch table detection whack-a-mole.  Add a check to
distinguish KASAN data reads from switch data reads.  The switch jump
tables in .rodata have relocations associated with them.

This fixes the following warning:

  crypto/asymmetric_keys/x509_cert_parser.o: warning: objtool: x509_note_pkey_algo()+0xa4: sibling call from callable instruction with modified stack frame

Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Arnd Bergmann <arnd@arndb.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/d7c8853022ad47d158cb81e953a40469fc08a95e.1519784382.git.jpoimboe@redhat.com

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 472e64e..46c1d23 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -925,7 +925,11 @@ static struct rela *find_switch_table(struct objtool_file *file,
                if (find_symbol_containing(file->rodata, text_rela->addend))
                        continue;
 
-               return find_rela_by_dest(file->rodata, text_rela->addend);
+               rodata_rela = find_rela_by_dest(file->rodata, text_rela->addend);
+               if (!rodata_rela)
+                       continue;
+
+               return rodata_rela;
        }
 
        return NULL;