[PATCH v2] riscv: Fix detecting FPU support in standard extension

[Samuel Holland]

On 11/5/22 01:02, Yu Chien Peter Lin wrote:
> We should check the string until it hits underscore, in case it
> searches for the letters in the custom extension. For example,
> "rv64imac_xandes" will be treated as D extension support since
> there is a "d" in "andes", resulting illegal instruction caused
> by initializing FCSR.
> 
> Signed-off-by: Yu Chien Peter Lin <peterlin at andestech.com>
> ---
>  arch/riscv/cpu/cpu.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/riscv/cpu/cpu.c b/arch/riscv/cpu/cpu.c
> index 52ab02519f..d34c8efce0 100644
> --- a/arch/riscv/cpu/cpu.c
> +++ b/arch/riscv/cpu/cpu.c
> @@ -36,6 +36,7 @@ static inline bool supports_extension(char ext)
>  #ifdef CONFIG_CPU
>  	struct udevice *dev;
>  	char desc[32];
> +	int i;
>  
>  	uclass_find_first_device(UCLASS_CPU, &dev);
>  	if (!dev) {
> @@ -43,9 +44,16 @@ static inline bool supports_extension(char ext)
>  		return false;
>  	}
>  	if (!cpu_get_desc(dev, desc, sizeof(desc))) {
> -		/* skip the first 4 characters (rv32|rv64) */
> -		if (strchr(desc + 4, ext))
> -			return true;
> +		/*
> +		 * skip the first 4 characters (rv32|rv64) and
> +		 * check until underscore
> +		 */

This probably works for the intended usage, but it is not guaranteed to
work. Underscores are allowed even between single-letter extensions. See
section 29.5 ("Underscores") of the unprivileged spec. Still, this is an
improvement, so:

Reviewed-by: Samuel Holland <samuel at sholland.org>

> +		for (i = 4; i < sizeof(desc); i++) {
> +			if (desc[i] == '_' || desc[i] == '\0')
> +				break;
> +			if (desc[i] == ext)
> +				return true;
> +		}
>  	}
>  
>  	return false;