[PATCH v2] lib: sbi: Improve fatal error handling

[Jessica Clarke]

On 30 Nov 2021, at 05:52, Anup Patel <anup.patel at wdc.com> wrote:
> 
> From: Jessica Clarke <jrtc27 at jrtc27.com>
> 
> BUG and BUG_ON are not informative and are rather lazy interfaces, only
> telling the user that something went wrong in a given function, but not
> what, requiring the user to find the sources corresponding to their
> firmware (which may not be available) and figure out how that BUG(_ON)
> was hit. Even SBI_ASSERT in its current form, which does include the
> condition that triggered it in the output, isn't necessarily very
> informative. In some cases, the error may be fixable by the user, but
> they need to know the problem in order to have any hope of fixing it.
> It's also a nuisance for developers, whose development trees may have
> changed significantly since the release in question being used, and so
> line numbers can make it harder for them to understand which error case
> a user has hit.
> 
> This patch introduces a new sbi_panic function which is printf-like,
> allowing detailed error messages to be printed to the console. BUG and
> BUG_ON are removed, since the former is just a worse form of sbi_panic
> and the latter is a worse version of SBI_ASSERT. Finally, SBI_ASSERT is
> augmented to take a set of arguments to pass to sbi_panic on failure,
> used like so (sbi_boot_print_hart's current error case, which currently
> manually calls sbi_printf and sbi_hart_hang):
> 
>  SBI_ASSERT(xlen >= 1, ("Error %d getting MISA XLEN\n", xlen));
> 
> The existing users of BUG are replaced with calls to sbi_panic along
> with informative error messages. BUG_ON and SBI_ASSERT were unused (and,
> in the case of SBI_ASSERT, remain unused).
> 
> Many existing users of sbi_hart_hang should be converted to use either
> sbi_panic or SBI_ASSERT after this commit.
> 
> Signed-off-by: Jessica Clarke <jrtc27 at jrtc27.com>
> Reviewed-by: Anup Patel <anup.patel at wdc.com>
> Reviewed-by: Xiang W <wxjstz at 126.com>
> ---
> Changes since v1:
> - Update patch suject
> - Fixed typo in patch description
> - Remove "#include <sbi/sbi_hart.h>" from sbi_console.h

Thanks for pushing this forward after I failed to get round to
submitting a v2 myself.

Jess

> ---
> include/sbi/sbi_console.h       | 23 +++++------------------
> lib/sbi/riscv_asm.c             |  7 ++++---
> lib/sbi/sbi_console.c           | 14 ++++++++++++++
> platform/generic/sifive_fu740.c |  1 +
> 4 files changed, 24 insertions(+), 21 deletions(-)
> 
> diff --git a/include/sbi/sbi_console.h b/include/sbi/sbi_console.h
> index 28b4a79..e15b55d 100644
> --- a/include/sbi/sbi_console.h
> +++ b/include/sbi/sbi_console.h
> @@ -11,7 +11,6 @@
> #define __SBI_CONSOLE_H__
> 
> #include <sbi/sbi_types.h>
> -#include <sbi/sbi_hart.h>
> 
> struct sbi_console_device {
> 	/** Name of the console device */
> @@ -44,6 +43,8 @@ int __printf(1, 2) sbi_printf(const char *format, ...);
> 
> int __printf(1, 2) sbi_dprintf(const char *format, ...);
> 
> +void __printf(1, 2) __attribute__((noreturn)) sbi_panic(const char *format, ...);
> +
> const struct sbi_console_device *sbi_console_get_device(void);
> 
> void sbi_console_set_device(const struct sbi_console_device *dev);
> @@ -52,23 +53,9 @@ struct sbi_scratch;
> 
> int sbi_console_init(struct sbi_scratch *scratch);
> 
> -#define BUG() do { \
> -	sbi_printf("BUG: failure at %s:%d/%s()!\n", \
> -		   __FILE__, __LINE__, __func__); \
> -	sbi_hart_hang(); \
> -} while (0)
> -
> -#define BUG_ON(cond) do { \
> -	if (cond)	\
> -		BUG();	\
> -} while (0)
> -
> -#define SBI_ASSERT(cond) do { \
> -	if (!(cond)) { \
> -		sbi_printf("ASSERT: %s:%d/%s(): Assertion `%s` failed.\n", \
> -			   __FILE__,__LINE__,__func__, #cond);\
> -		sbi_hart_hang(); \
> -	} \
> +#define SBI_ASSERT(cond, args) do { \
> +	if (unlikely(!(cond))) \
> +		sbi_panic args; \
> } while (0)
> 
> #endif
> diff --git a/lib/sbi/riscv_asm.c b/lib/sbi/riscv_asm.c
> index 1642ac6..2e2e148 100644
> --- a/lib/sbi/riscv_asm.c
> +++ b/lib/sbi/riscv_asm.c
> @@ -76,7 +76,8 @@ void misa_string(int xlen, char *out, unsigned int out_sz)
> 			out[pos++] = '8';
> 			break;
> 		default:
> -			BUG();
> +			sbi_panic("%s: Unknown misa.MXL encoding %d",
> +				   __func__, xlen);
> 			return;
> 		}
> 	}
> @@ -145,7 +146,7 @@ unsigned long csr_read_num(int csr_num)
> #endif
> 
> 	default:
> -		BUG();
> +		sbi_panic("%s: Unknown CSR %#x", __func__, csr_num);
> 		break;
> 	};
> 
> @@ -213,7 +214,7 @@ void csr_write_num(int csr_num, unsigned long val)
> 	switchcase_csr_write_16(CSR_MHPMEVENT16, val)
> 
> 	default:
> -		BUG();
> +		sbi_panic("%s: Unknown CSR %#x", __func__, csr_num);
> 		break;
> 	};
> 
> diff --git a/lib/sbi/sbi_console.c b/lib/sbi/sbi_console.c
> index 29eede3..34c843d 100644
> --- a/lib/sbi/sbi_console.c
> +++ b/lib/sbi/sbi_console.c
> @@ -9,6 +9,7 @@
> 
> #include <sbi/riscv_locks.h>
> #include <sbi/sbi_console.h>
> +#include <sbi/sbi_hart.h>
> #include <sbi/sbi_platform.h>
> #include <sbi/sbi_scratch.h>
> 
> @@ -397,6 +398,19 @@ int sbi_dprintf(const char *format, ...)
> 	return retval;
> }
> 
> +void sbi_panic(const char *format, ...)
> +{
> +	va_list args;
> +
> +	spin_lock(&console_out_lock);
> +	va_start(args, format);
> +	print(NULL, NULL, format, args);
> +	va_end(args);
> +	spin_unlock(&console_out_lock);
> +
> +	sbi_hart_hang();
> +}
> +
> const struct sbi_console_device *sbi_console_get_device(void)
> {
> 	return console_dev;
> diff --git a/platform/generic/sifive_fu740.c b/platform/generic/sifive_fu740.c
> index 3152152..333b3fb 100644
> --- a/platform/generic/sifive_fu740.c
> +++ b/platform/generic/sifive_fu740.c
> @@ -12,6 +12,7 @@
> #include <platform_override.h>
> #include <libfdt.h>
> #include <sbi/sbi_error.h>
> +#include <sbi/sbi_hart.h>
> #include <sbi/sbi_system.h>
> #include <sbi/sbi_console.h>
> #include <sbi_utils/fdt/fdt_helper.h>
> -- 
> 2.25.1
>