objtool: Fix another GCC jump table detection issue

Arnd Bergmann reported a (false positive) objtool warning:

  drivers/infiniband/sw/rxe/rxe_resp.o: warning: objtool: rxe_responder()+0xfe: sibling call from callable instruction with changed frame pointer

The issue is in find_switch_table().  It tries to find a switch
statement's jump table by walking backwards from an indirect jump
instruction, looking for a relocation to the .rodata section.  In this
case it stopped walking prematurely: the first .rodata relocation it
encountered was for a variable (resp_state_name) instead of a jump
table, so it just assumed there wasn't a jump table.

The fix is to ignore any .rodata relocation which refers to an ELF
object symbol.  This works because the jump tables are anonymous and
have no symbols associated with them.

Reported-by: Arnd Bergmann <arnd@arndb.de>
Tested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 3732710ff6f2 ("objtool: Improve rare switch jump table pattern detection")
Link: http://lkml.kernel.org/r/20170302225723.3ndbsnl4hkqbne7a@treble
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index 4cfdbb5b696783cbeb097f04220c180e7e87e82a..066086dd59a8017e293993a50d2f432d47441cfe 100644 (file)
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -805,11 +805,20 @@ static struct rela *find_switch_table(struct objtool_file *file,
                     insn->jump_dest->offset > orig_insn->offset))
                    break;
 
+               /* look for a relocation which references .rodata */
                text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
                                                    insn->len);
-               if (text_rela && text_rela->sym == file->rodata->sym)
-                       return find_rela_by_dest(file->rodata,
-                                                text_rela->addend);
+               if (!text_rela || text_rela->sym != file->rodata->sym)
+                       continue;
+
+               /*
+                * Make sure the .rodata address isn't associated with a
+                * symbol.  gcc jump tables are anonymous data.
+                */
+               if (find_symbol_containing(file->rodata, text_rela->addend))
+                       continue;
+
+               return find_rela_by_dest(file->rodata, text_rela->addend);
        }
 
        return NULL;

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 0d7983ac63ef9e300110d9a6ec6771a75378784e..d897702ce7427804da2c09387f674077f22accc5 100644 (file)
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -85,6 +85,18 @@ struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset)
        return NULL;
 }
 
+struct symbol *find_symbol_containing(struct section *sec, unsigned long offset)
+{
+       struct symbol *sym;
+
+       list_for_each_entry(sym, &sec->symbol_list, list)
+               if (sym->type != STT_SECTION &&
+                   offset >= sym->offset && offset < sym->offset + sym->len)
+                       return sym;
+
+       return NULL;
+}
+
 struct rela *find_rela_by_dest_range(struct section *sec, unsigned long offset,
                                     unsigned int len)
 {

diff --git a/tools/objtool/elf.h b/tools/objtool/elf.h
index aa1ff6596684f9304d0dd4bd3165f819b4dcdaf7..731973e1a3f5eb6bb1d6e67890c54c1440f237f3 100644 (file)
--- a/tools/objtool/elf.h
+++ b/tools/objtool/elf.h
@@ -79,6 +79,7 @@ struct elf {
 struct elf *elf_open(const char *name);
 struct section *find_section_by_name(struct elf *elf, const char *name);
 struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset);
+struct symbol *find_symbol_containing(struct section *sec, unsigned long offset);
 struct rela *find_rela_by_dest(struct section *sec, unsigned long offset);
 struct rela *find_rela_by_dest_range(struct section *sec, unsigned long offset,
                                     unsigned int len);