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From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	x86@kernel.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Denys Vlasenko <dvlasenk@redhat.com>
Subject: [PATCH] objtool: fix another gcc jump table detection issue
Date: Thu, 2 Mar 2017 16:57:23 -0600
Message-ID: <20170302225723.3ndbsnl4hkqbne7a@treble> (raw)
In-Reply-To: <CAK8P3a1BLODnHGLZHeVzFdjFjKCju=5Yit=JfyPvDgTOkA2QZw@mail.gmail.com>


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>
Fixes: 3732710ff6f2 ("objtool: Improve rare switch jump table pattern detection")
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
 tools/objtool/builtin-check.c | 15 ++++++++++++---
 tools/objtool/elf.c           | 12 ++++++++++++
 tools/objtool/elf.h           |  1 +
 3 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index 5fc52ee..c2a8518 100644
--- 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 0d7983a..d897702 100644
--- 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 aa1ff65..731973e 100644
--- 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);
-- 
2.7.4

  reply index

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-10-10 12:56 [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings Arnd Bergmann
2016-10-10 20:23 ` Josh Poimboeuf
2016-10-11  8:08   ` Arnd Bergmann
2016-10-11 12:20     ` Josh Poimboeuf
2016-10-11 13:30       ` Arnd Bergmann
2016-10-11 15:05         ` Josh Poimboeuf
2016-10-11 15:51           ` Josh Poimboeuf
2016-10-11 20:38             ` Arnd Bergmann
2016-10-12 13:01               ` Josh Poimboeuf
2016-10-13 12:46               ` Another gcc corruption bug (was Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings) Josh Poimboeuf
2016-10-13 17:57                 ` Denys Vlasenko
2016-10-13 20:15                   ` Josh Poimboeuf
2017-03-01  9:34               ` [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings Arnd Bergmann
2017-03-01  9:45                 ` Arnd Bergmann
2017-03-01 14:40                   ` Josh Poimboeuf
2017-03-01 15:27                     ` Arnd Bergmann
2017-03-01 16:53                       ` Josh Poimboeuf
2017-03-01 22:05                         ` Arnd Bergmann
2017-03-01 22:42                         ` Arnd Bergmann
2017-03-02  1:03                           ` Josh Poimboeuf
2017-03-02  6:31                             ` Ingo Molnar
2017-03-02 12:49                               ` Josh Poimboeuf
2017-03-02 13:46                                 ` Ingo Molnar
2017-03-02 14:08                                   ` Josh Poimboeuf
2017-03-02 14:46                                     ` Ingo Molnar
2017-03-02 22:49                             ` Arnd Bergmann
2017-03-02 23:05                               ` Josh Poimboeuf
2017-03-03  8:58                                 ` Arnd Bergmann
2017-03-03 11:27                                   ` Arnd Bergmann
2017-03-01 14:31                 ` Josh Poimboeuf
2017-03-01 15:21                   ` Arnd Bergmann
2017-03-02 18:25                     ` Josh Poimboeuf
2017-03-02 22:43                       ` Arnd Bergmann
2017-03-02 22:57                         ` Josh Poimboeuf [this message]
2017-03-02 23:01                           ` [PATCH] objtool: fix another gcc jump table detection issue Arnd Bergmann
2016-10-11  1:53 ` [PATCH] objtool: support '-mtune=atom' stack frame setup instruction Josh Poimboeuf

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