linux-kernel - [RFC PATCH 3/5] x86: Add support for suppressing warning tracebacks

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Message-Id: <20240305184033.425294-4-linux@roeck-us.net>
Date: Tue,  5 Mar 2024 10:40:31 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: linux-kselftest@...r.kernel.org
Cc: David Airlie <airlied@...il.com>,
	Arnd Bergmann <arnd@...db.de>,
	Maíra Canal <mcanal@...lia.com>,
	Dan Carpenter <dan.carpenter@...aro.org>,
	Kees Cook <keescook@...omium.org>,
	Daniel Diaz <daniel.diaz@...aro.org>,
	David Gow <davidgow@...gle.com>,
	Arthur Grillo <arthurgrillo@...eup.net>,
	Brendan Higgins <brendan.higgins@...ux.dev>,
	Naresh Kamboju <naresh.kamboju@...aro.org>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Maxime Ripard <mripard@...nel.org>,
	Ville Syrjälä <ville.syrjala@...ux.intel.com>,
	Daniel Vetter <daniel@...ll.ch>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org,
	loongarch@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org,
	kunit-dev@...glegroups.com,
	linux-arch@...r.kernel.org,
	Guenter Roeck <linux@...ck-us.net>
Subject: [RFC PATCH 3/5] x86: Add support for suppressing warning tracebacks

Add support for selectively suppressing WARNING tracebacks to x86.
This requires adding the function triggering tracebacks to the __bug_table
object section.

To limit image size impact, the pointer to the function name is only added
to the __bug_table section if both CONFIG_KUNIT and CONFIG_DEBUG_BUGVERBOSE
are enabled. Otherwise, the __func__ assembly parameter is replaced with a
(dummy) NULL parameter to avoid an image size increase due to unused
__func__ entries (this is necessary because __func__ is not a define but a
virtual variable).

Signed-off-by: Guenter Roeck <linux@...ck-us.net>
---
 arch/x86/include/asm/bug.h | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
index a3ec87d198ac..8e45143fa676 100644
--- a/arch/x86/include/asm/bug.h
+++ b/arch/x86/include/asm/bug.h
@@ -21,6 +21,15 @@
 # define __BUG_REL(val)	".long " __stringify(val) " - ."
 #endif
 
+#if IS_ENABLED(CONFIG_KUNIT)
+# define HAVE_BUG_FUNCTION
+# define __BUG_FUNC_PTR	__BUG_REL(%c1)
+# define __BUG_FUNC	__func__
+#else
+# define __BUG_FUNC_PTR
+# define __BUG_FUNC	NULL
+#endif /* IS_ENABLED(CONFIG_KUNIT) */
+
 #ifdef CONFIG_DEBUG_BUGVERBOSE
 
 #define _BUG_FLAGS(ins, flags, extra)					\
@@ -29,12 +38,13 @@ do {									\
 		     ".pushsection __bug_table,\"aw\"\n"		\
 		     "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n"	\
 		     "\t"  __BUG_REL(%c0) "\t# bug_entry::file\n"	\
-		     "\t.word %c1"        "\t# bug_entry::line\n"	\
-		     "\t.word %c2"        "\t# bug_entry::flags\n"	\
-		     "\t.org 2b+%c3\n"					\
+		     "\t"  __BUG_FUNC_PTR "\t# bug_entry::function\n"	\
+		     "\t.word %c2"        "\t# bug_entry::line\n"	\
+		     "\t.word %c3"        "\t# bug_entry::flags\n"	\
+		     "\t.org 2b+%c4\n"					\
 		     ".popsection\n"					\
 		     extra						\
-		     : : "i" (__FILE__), "i" (__LINE__),		\
+		     : : "i" (__FILE__), "i" (__BUG_FUNC), "i" (__LINE__),\
 			 "i" (flags),					\
 			 "i" (sizeof(struct bug_entry)));		\
 } while (0)
@@ -80,7 +90,8 @@ do {								\
 do {								\
 	__auto_type __flags = BUGFLAG_WARNING|(flags);		\
 	instrumentation_begin();				\
-	_BUG_FLAGS(ASM_UD2, __flags, ASM_REACHABLE);		\
+	if (!IS_SUPPRESSED_WARNING(__func__))			\
+		_BUG_FLAGS(ASM_UD2, __flags, ASM_REACHABLE);	\
 	instrumentation_end();					\
 } while (0)
 
-- 
2.39.2