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Date:   Thu, 13 Apr 2023 10:48:01 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Josh Poimboeuf <jpoimboe@kernel.org>
Cc:     x86@kernel.org, linux-kernel@vger.kernel.org,
        Miroslav Benes <mbenes@suse.cz>
Subject: Re: [PATCH v2 8/9] objtool: Detect missing __noreturn annotations
Message-ID: <20230413084801.GI4253@hirez.programming.kicks-ass.net>
References: <cover.1681325924.git.jpoimboe@kernel.org>
 <0f630a0eb4585ab4114e4eecaa6f166a1fd81d49.1681325924.git.jpoimboe@kernel.org>
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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@kernel.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) ?

---
 tools/objtool/Makefile     |  1 +
 tools/objtool/check.c      | 27 +--------------------------
 tools/objtool/noreturns    | 26 ++++++++++++++++++++++++++
 tools/objtool/noreturns.sh |  7 +++++++
 4 files changed, 35 insertions(+), 26 deletions(-)

diff --git a/tools/objtool/Makefile b/tools/objtool/Makefile
index 83b100c1e7f6..50b6cd241571 100644
--- a/tools/objtool/Makefile
+++ b/tools/objtool/Makefile
@@ -63,6 +63,7 @@ include $(srctree)/tools/build/Makefile.include
 
 $(OBJTOOL_IN): fixdep $(LIBSUBCMD) FORCE
 	$(Q)$(CONFIG_SHELL) ./sync-check.sh
+	$(Q)$(CONFIG_SHELL) ./noreturns.sh
 	$(Q)$(MAKE) $(build)=objtool $(HOST_OVERRIDES) CFLAGS="$(OBJTOOL_CFLAGS)" \
 		LDFLAGS="$(OBJTOOL_LDFLAGS)"
 
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index f937be1afe65..f558730c27b6 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -197,32 +197,7 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 	 * 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",
-		"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"
 	};
 
 	if (!func)
diff --git a/tools/objtool/noreturns b/tools/objtool/noreturns
new file mode 100644
index 000000000000..75f35fbb34d1
--- /dev/null
+++ b/tools/objtool/noreturns
@@ -0,0 +1,26 @@
+__invalid_creds
+__module_put_and_kthread_exit
+__reiserfs_panic
+__stack_chk_fail
+__ubsan_handle_builtin_unreachable
+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
diff --git a/tools/objtool/noreturns.sh b/tools/objtool/noreturns.sh
new file mode 100755
index 000000000000..f728cb61e665
--- /dev/null
+++ b/tools/objtool/noreturns.sh
@@ -0,0 +1,7 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+
+cat noreturns | while read func
+do
+	echo \"${func}\",
+done > noreturns.h