Re: [PATCH v3 14/15] riscv: Add support for suppressing warning backtraces

[Charlie Jenkins <charlie@rivosinc.com>]

On Wed, Apr 03, 2024 at 06:19:35AM -0700, Guenter Roeck wrote:
> 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).
> 
> To simplify the implementation, unify the __BUG_ENTRY_ADDR and
> __BUG_ENTRY_FILE macros into a single macro named __BUG_REL() which takes
> the address, file, or function reference as parameter.
> 
> Tested-by: Linux Kernel Functional Testing <lkft@linaro.org>
> Acked-by: Dan Carpenter <dan.carpenter@linaro.org>
> Cc: Paul Walmsley <paul.walmsley@sifive.com>
> Cc: Palmer Dabbelt <palmer@dabbelt.com>
> Cc: Albert Ou <aou@eecs.berkeley.edu>
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> ---
> v2:
> - Rebased to v6.9-rc1
> - Added Tested-by:, Acked-by:, and Reviewed-by: tags
> - Introduced KUNIT_SUPPRESS_BACKTRACE configuration option
> v3:
> - Rebased to v6.9-rc2
> 
>  arch/riscv/include/asm/bug.h | 38 ++++++++++++++++++++++++------------
>  1 file changed, 26 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/bug.h b/arch/riscv/include/asm/bug.h
> index 1aaea81fb141..79f360af4ad8 100644
> --- a/arch/riscv/include/asm/bug.h
> +++ b/arch/riscv/include/asm/bug.h
> @@ -30,26 +30,39 @@
>  typedef u32 bug_insn_t;
>  
>  #ifdef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
> -#define __BUG_ENTRY_ADDR	RISCV_INT " 1b - ."
> -#define __BUG_ENTRY_FILE	RISCV_INT " %0 - ."
> +#define __BUG_REL(val)	RISCV_INT " " __stringify(val) " - ."
>  #else
> -#define __BUG_ENTRY_ADDR	RISCV_PTR " 1b"
> -#define __BUG_ENTRY_FILE	RISCV_PTR " %0"
> +#define __BUG_REL(val)	RISCV_PTR " " __stringify(val)
>  #endif
>  
>  #ifdef CONFIG_DEBUG_BUGVERBOSE
> +
> +#ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
> +# define HAVE_BUG_FUNCTION
> +# define __BUG_FUNC_PTR	__BUG_REL(%1)
> +#else
> +# define __BUG_FUNC_PTR
> +#endif /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
> +
>  #define __BUG_ENTRY			\
> -	__BUG_ENTRY_ADDR "\n\t"		\
> -	__BUG_ENTRY_FILE "\n\t"		\
> -	RISCV_SHORT " %1\n\t"		\
> -	RISCV_SHORT " %2"
> +	__BUG_REL(1b) "\n\t"		\
> +	__BUG_REL(%0) "\n\t"		\
> +	__BUG_FUNC_PTR "\n\t"		\
> +	RISCV_SHORT " %2\n\t"		\
> +	RISCV_SHORT " %3"
>  #else
>  #define __BUG_ENTRY			\
> -	__BUG_ENTRY_ADDR "\n\t"		\
> -	RISCV_SHORT " %2"
> +	__BUG_REL(1b) "\n\t"		\
> +	RISCV_SHORT " %3"
>  #endif
>  
>  #ifdef CONFIG_GENERIC_BUG
> +#ifdef HAVE_BUG_FUNCTION
> +# define __BUG_FUNC	__func__
> +#else
> +# define __BUG_FUNC	NULL
> +#endif
> +
>  #define __BUG_FLAGS(flags)					\
>  do {								\
>  	__asm__ __volatile__ (					\
> @@ -58,10 +71,11 @@ do {								\
>  			".pushsection __bug_table,\"aw\"\n\t"	\
>  		"2:\n\t"					\
>  			__BUG_ENTRY "\n\t"			\
> -			".org 2b + %3\n\t"                      \
> +			".org 2b + %4\n\t"                      \
>  			".popsection"				\
>  		:						\
> -		: "i" (__FILE__), "i" (__LINE__),		\
> +		: "i" (__FILE__), "i" (__BUG_FUNC),		\
> +		  "i" (__LINE__),				\
>  		  "i" (flags),					\
>  		  "i" (sizeof(struct bug_entry)));              \
>  } while (0)
> -- 
> 2.39.2
> 
> 
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Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>

- Charlie