linux-kernel - Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings

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Date:   Thu, 2 Mar 2017 12:25:15 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Denys Vlasenko <dvlasenk@...hat.com>
Subject: Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings

On Wed, Mar 01, 2017 at 04:21:36PM +0100, Arnd Bergmann wrote:
> On Wed, Mar 1, 2017 at 3:31 PM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> > On Wed, Mar 01, 2017 at 10:34:42AM +0100, Arnd Bergmann wrote:
> >> On Tue, Oct 11, 2016 at 10:38 PM, Arnd Bergmann <arnd@...db.de> wrote:
> >> > On Tuesday, October 11, 2016 10:51:46 AM CEST Josh Poimboeuf wrote:
> >> >>
> >> >> 3) 0xFC244C03-config:
> >> >> drivers/scsi/fnic/fnic_main.o: warning: objtool: fnic_log_q_error() falls through to next function fnic_handle_link_event()
> >> >> drivers/scsi/snic/snic_res.o: warning: objtool: .text: unexpected end of section
> >> >>
> >> >> These look like another bad gcc bug which is truncating functions:
> >> >
> >> > Same bug for both of them?
> >>
> >> I ran into this one again today, after updating to the latest gcc-7.0.1:
> >>
> >> drivers/infiniband/sw/rxe/rxe_resp.o: warning: objtool:
> >> rxe_responder()+0xfe: sibling call from callable instruction with
> >> changed frame pointer
> >>
> >> Josh, did you get around to updating objtool the last time I reported it, or
> >> is it still the same problem? If this is a new variation, I can provide more
> >> details about the failure, otherwise I'll just ignore it for now.
> >
> > This one should have been fixed with:
> >
> >   3732710ff6f2 ("objtool: Improve rare switch jump table pattern detection")
> 
> It was on the current linux-next, so that commit should certainly be included.
> 
> > Can you attach the object file?

Here's the preliminary fix for this one (still needs more testing):

diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index bd12eb1..7b718bb 100644
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -806,11 +806,20 @@ static struct rela *find_switch_table(struct objtool_file *file,
 		     insn->jump_dest->offset > orig_insn->offset))
 		    break;
 
+		/* look for a rela 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);