diff mbox series

[v4,07/14] arm64: Add support for suppressing warning backtraces

Message ID 20250313114329.284104-8-acarmina@redhat.com (mailing list archive)
State New
Headers show
Series Add support for suppressing warning backtraces | expand

Commit Message

Alessandro Carminati March 13, 2025, 11:43 a.m. UTC 
From: Guenter Roeck <linux@roeck-us.net>

Add name of functions triggering warning backtraces to the __bug_table
object section to enable support for suppressing WARNING backtraces.

To limit image size impact, the pointer to the function name is only added
to the __bug_table section if both CONFIG_KUNIT_SUPPRESS_BACKTRACE 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).

Tested-by: Linux Kernel Functional Testing <lkft@linaro.org>
Acked-by: Dan Carpenter <dan.carpenter@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
---
 arch/arm64/include/asm/asm-bug.h | 27 ++++++++++++++++++---------
 arch/arm64/include/asm/bug.h     |  8 +++++++-
 2 files changed, 25 insertions(+), 10 deletions(-)

Comments

Will Deacon March 13, 2025, 12:25 p.m. UTC | #1 
On Thu, Mar 13, 2025 at 11:43:22AM +0000, Alessandro Carminati wrote:
> diff --git a/arch/arm64/include/asm/bug.h b/arch/arm64/include/asm/bug.h
> index 28be048db3f6..044c5e24a17d 100644
> --- a/arch/arm64/include/asm/bug.h
> +++ b/arch/arm64/include/asm/bug.h
> @@ -11,8 +11,14 @@
>  
>  #include <asm/asm-bug.h>
>  
> +#ifdef HAVE_BUG_FUNCTION
> +# define __BUG_FUNC	__func__
> +#else
> +# define __BUG_FUNC	NULL
> +#endif
> +
>  #define __BUG_FLAGS(flags)				\
> -	asm volatile (__stringify(ASM_BUG_FLAGS(flags)));
> +	asm volatile (__stringify(ASM_BUG_FLAGS(flags, %c0)) : : "i" (__BUG_FUNC));

Why is 'i' the right asm constraint to use here? It seems a bit odd to
use that for a pointer.

Will
Alessandro Carminati March 13, 2025, 4:40 p.m. UTC | #2 
Hello Will,

On Thu, Mar 13, 2025 at 1:25 PM Will Deacon <will@kernel.org> wrote:
>
> On Thu, Mar 13, 2025 at 11:43:22AM +0000, Alessandro Carminati wrote:
> > diff --git a/arch/arm64/include/asm/bug.h b/arch/arm64/include/asm/bug.h
> > index 28be048db3f6..044c5e24a17d 100644
> > --- a/arch/arm64/include/asm/bug.h
> > +++ b/arch/arm64/include/asm/bug.h
> > @@ -11,8 +11,14 @@
> >
> >  #include <asm/asm-bug.h>
> >
> > +#ifdef HAVE_BUG_FUNCTION
> > +# define __BUG_FUNC  __func__
> > +#else
> > +# define __BUG_FUNC  NULL
> > +#endif
> > +
> >  #define __BUG_FLAGS(flags)                           \
> > -     asm volatile (__stringify(ASM_BUG_FLAGS(flags)));
> > +     asm volatile (__stringify(ASM_BUG_FLAGS(flags, %c0)) : : "i" (__BUG_FUNC));
>
> Why is 'i' the right asm constraint to use here? It seems a bit odd to
> use that for a pointer.

I received this code as legacy from a previous version.
In my review, I considered the case when HAVE_BUG_FUNCTION is defined:
Here, __BUG_FUNC is defined as __func__, which is the name of the
current function as a string literal.
Using the constraint "i" seems appropriate to me in this case.

However, when HAVE_BUG_FUNCTION is not defined:
__BUG_FUNC is defined as NULL. Initially, I considered it literal 0,
but after investigating your concern, I found:

```
$ echo -E "#include <stdio.h>\n#include <stddef.h>\nint main()
{\nreturn 0;\n}" | aarch64-linux-gnu-gcc -E -dM - | grep NULL
#define NULL ((void *)0)
```

I realized that NULL is actually a pointer that is not a link time
symbol, and using the "i" constraint with NULL may result in undefined
behavior.

Would the following alternative definition for __BUG_FUNC be more convincing?

```
#ifdef HAVE_BUG_FUNCTION
    #define __BUG_FUNC __func__
#else
    #define __BUG_FUNC (uintptr_t)0
#endif
```
Let me know your thoughts.

>
> Will
>



--
---
172
diff mbox series

Patch

diff --git a/arch/arm64/include/asm/asm-bug.h b/arch/arm64/include/asm/asm-bug.h
index 6e73809f6492..bf0a5ba81611 100644
--- a/arch/arm64/include/asm/asm-bug.h
+++ b/arch/arm64/include/asm/asm-bug.h
@@ -8,37 +8,46 @@ 
 #include <asm/brk-imm.h>
 
 #ifdef CONFIG_DEBUG_BUGVERBOSE
-#define _BUGVERBOSE_LOCATION(file, line) __BUGVERBOSE_LOCATION(file, line)
-#define __BUGVERBOSE_LOCATION(file, line)			\
+
+#ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
+# define HAVE_BUG_FUNCTION
+# define __BUG_FUNC_PTR(func)	.long func - .;
+#else
+# define __BUG_FUNC_PTR(func)
+#endif
+
+#define _BUGVERBOSE_LOCATION(file, func, line) __BUGVERBOSE_LOCATION(file, func, line)
+#define __BUGVERBOSE_LOCATION(file, func, line)		\
 		.pushsection .rodata.str,"aMS",@progbits,1;	\
 	14472:	.string file;					\
 		.popsection;					\
 								\
 		.long 14472b - .;				\
+		__BUG_FUNC_PTR(func)				\
 		.short line;
 #else
-#define _BUGVERBOSE_LOCATION(file, line)
+#define _BUGVERBOSE_LOCATION(file, func, line)
 #endif
 
 #ifdef CONFIG_GENERIC_BUG
 
-#define __BUG_ENTRY(flags) 				\
+#define __BUG_ENTRY(flags, func)			\
 		.pushsection __bug_table,"aw";		\
 		.align 2;				\
 	14470:	.long 14471f - .;			\
-_BUGVERBOSE_LOCATION(__FILE__, __LINE__)		\
+_BUGVERBOSE_LOCATION(__FILE__, func, __LINE__)		\
 		.short flags; 				\
 		.align 2;				\
 		.popsection;				\
 	14471:
 #else
-#define __BUG_ENTRY(flags)
+#define __BUG_ENTRY(flags, func)
 #endif
 
-#define ASM_BUG_FLAGS(flags)				\
-	__BUG_ENTRY(flags)				\
+#define ASM_BUG_FLAGS(flags, func)			\
+	__BUG_ENTRY(flags, func)			\
 	brk	BUG_BRK_IMM
 
-#define ASM_BUG()	ASM_BUG_FLAGS(0)
+#define ASM_BUG()	ASM_BUG_FLAGS(0, .)
 
 #endif /* __ASM_ASM_BUG_H */
diff --git a/arch/arm64/include/asm/bug.h b/arch/arm64/include/asm/bug.h
index 28be048db3f6..044c5e24a17d 100644
--- a/arch/arm64/include/asm/bug.h
+++ b/arch/arm64/include/asm/bug.h
@@ -11,8 +11,14 @@ 
 
 #include <asm/asm-bug.h>
 
+#ifdef HAVE_BUG_FUNCTION
+# define __BUG_FUNC	__func__
+#else
+# define __BUG_FUNC	NULL
+#endif
+
 #define __BUG_FLAGS(flags)				\
-	asm volatile (__stringify(ASM_BUG_FLAGS(flags)));
+	asm volatile (__stringify(ASM_BUG_FLAGS(flags, %c0)) : : "i" (__BUG_FUNC));
 
 #define BUG() do {					\
 	__BUG_FLAGS(0);					\