linux-kernel - Re: [PATCH v2 8/9] objtool: Detect missing _

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Date:   Thu, 13 Apr 2023 08:19:36 -0700
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Miroslav Benes <mbenes@...e.cz>
Subject: Re: [PATCH v2 8/9] objtool: Detect missing __noreturn annotations

On Thu, Apr 13, 2023 at 10:48:01AM +0200, Peter Zijlstra wrote:
> On Wed, Apr 12, 2023 at 12:03:23PM -0700, Josh Poimboeuf wrote:
> > Most "unreachable instruction" warnings these days seem to actually be
> > the result of a missing __noreturn annotation.  Add an explicit check
> > for that.
> > 
> > Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
> > ---
> >  tools/objtool/Documentation/objtool.txt |  6 ++++++
> >  tools/objtool/check.c                   | 14 +++++++++++++-
> >  2 files changed, 19 insertions(+), 1 deletion(-)
> > 
> > diff --git a/tools/objtool/Documentation/objtool.txt b/tools/objtool/Documentation/objtool.txt
> > index 5a69c207a10e..2cd1fa16ed08 100644
> > --- a/tools/objtool/Documentation/objtool.txt
> > +++ b/tools/objtool/Documentation/objtool.txt
> > @@ -303,6 +303,12 @@ the objtool maintainers.
> >     If it's not actually in a callable function (e.g. kernel entry code),
> >     change ENDPROC to END.
> >  
> > +3. file.o: warning: objtool: foo+0x48c: bar() is missing a __noreturn annotation
> > +
> > +   The call from foo() to bar() doesn't return, but bar() is missing the
> > +   __noreturn annotation.  NOTE: In addition to adding the __noreturn
> > +   annotation, the function name also needs to be added to
> > +   'global_noreturns' in tools/objtool/check.c.
> 
> Do we want something like the below (except perhaps less horrible) ?

Yeah, maybe.  Another possible way to do it:

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index cae6ac6ff246..a4e8ff9dabf1 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -192,39 +192,16 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 	struct instruction *insn;
 	bool empty = true;
 
+#define NORETURN(func) "\"" __stringify(func) "\"",
+
 	/*
 	 * Unfortunately these have to be hard coded because the noreturn
 	 * attribute isn't provided in ELF data. Keep 'em sorted.
 	 */
 	static const char * const global_noreturns[] = {
-		"__invalid_creds",
-		"__module_put_and_kthread_exit",
-		"__reiserfs_panic",
-		"__stack_chk_fail",
-		"__ubsan_handle_builtin_unreachable",
-		"arch_cpu_idle_dead",
-		"cpu_bringup_and_idle",
-		"cpu_startup_entry",
-		"do_exit",
-		"do_group_exit",
-		"do_task_dead",
-		"ex_handler_msr_mce",
-		"fortify_panic",
-		"kthread_complete_and_exit",
-		"kthread_exit",
-		"kunit_try_catch_throw",
-		"lbug_with_loc",
-		"machine_real_restart",
-		"make_task_dead",
-		"panic",
-		"rewind_stack_and_make_dead",
-		"sev_es_terminate",
-		"snp_abort",
-		"stop_this_cpu",
-		"usercopy_abort",
-		"xen_cpu_bringup_again",
-		"xen_start_kernel",
+#include "noreturns.h"
 	};
+#undef NORETURN
 
 	if (!func)
 		return false;
diff --git a/tools/objtool/noreturns.h b/tools/objtool/noreturns.h
new file mode 100644
index 000000000000..0f5e53fd9e7a
--- /dev/null
+++ b/tools/objtool/noreturns.h
@@ -0,0 +1,27 @@
+NORETURN(__invalid_creds)
+NORETURN(__module_put_and_kthread_exit)
+NORETURN(__reiserfs_panic)
+NORETURN(__stack_chk_fail)
+NORETURN(__ubsan_handle_builtin_unreachable)
+NORETURN(arch_cpu_idle_dead)
+NORETURN(cpu_bringup_and_idle)
+NORETURN(cpu_startup_entry)
+NORETURN(do_exit)
+NORETURN(do_group_exit)
+NORETURN(do_task_dead)
+NORETURN(ex_handler_msr_mce)
+NORETURN(fortify_panic)
+NORETURN(kthread_complete_and_exit)
+NORETURN(kthread_exit)
+NORETURN(kunit_try_catch_throw)
+NORETURN(lbug_with_loc)
+NORETURN(machine_real_restart)
+NORETURN(make_task_dead)
+NORETURN(panic)
+NORETURN(rewind_stack_and_make_dead)
+NORETURN(sev_es_terminate)
+NORETURN(snp_abort)
+NORETURN(stop_this_cpu)
+NORETURN(usercopy_abort)
+NORETURN(xen_cpu_bringup_again)
+NORETURN(xen_start_kernel)