Re: [PATCH 3/4] RISC-V: export the ISA string of the running machine in the aux vector

[Andrew Jones]

On Mon, Apr 24, 2023 at 09:49:10PM +0200, Heiko Stuebner wrote:
> From: Heiko Stuebner <heiko.stuebner@xxxxxxxx>
> 
> Already defined aux-vectors regarding the machine type are AT_PLATFORM
> and AT_BASE_PLATFORM. PPC already uses AT_BASE_PLATFORM to identify the
> real platform the system is running on, so do a similar thing on RISC-V
> and export the ISA string of the running machine via this aux-vector
> element.
> 
> This way userspace can possibly adapt to extensions that allow it to
> run certain loads more performantly.
> 
> Signed-off-by: Heiko Stuebner <heiko.stuebner@xxxxxxxx>
> ---
>  arch/riscv/include/asm/elf.h | 10 ++++++++++
>  arch/riscv/kernel/cpu.c      | 12 ++++++++++++
>  2 files changed, 22 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/elf.h b/arch/riscv/include/asm/elf.h
> index 30e7d2455960..820ef627e83d 100644
> --- a/arch/riscv/include/asm/elf.h
> +++ b/arch/riscv/include/asm/elf.h
> @@ -78,6 +78,16 @@ extern unsigned long elf_hwcap;
>  
>  #define COMPAT_ELF_PLATFORM	(NULL)
>  
> +/*
> + * ELF_PLATFORM indicates the ISA supported by the platform, but has
> + * special meaning to ld.so .
                              ^ stray space

> + * Expose the ISA string including all usable extensions via
> + * ELF_BASE_PLATFORM instead and allow userspace to adapt to them
> + * if needed.
> + */
> +#define ELF_BASE_PLATFORM (riscv_base_platform)
> +extern const char *riscv_base_platform;
> +
>  #ifdef CONFIG_MMU
>  #define ARCH_DLINFO						\
>  do {								\
> diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
> index 06c2f587a176..71770563199f 100644
> --- a/arch/riscv/kernel/cpu.c
> +++ b/arch/riscv/kernel/cpu.c
> @@ -118,8 +118,12 @@ static int riscv_cpuinfo_starting(unsigned int cpu)
>  	return 0;
>  }
>  
> +const char *riscv_base_platform = NULL;

No need for the '= NULL'

> +static char *riscv_create_isa_string(void);
> +
>  static int __init riscv_cpuinfo_init(void)
>  {
> +	char *isa_str;
>  	int ret;
>  
>  	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "riscv/cpuinfo:starting",
> @@ -129,6 +133,14 @@ static int __init riscv_cpuinfo_init(void)
>  		return ret;
>  	}
>  
> +	/*
> +	 * Create the isa-string with the common set of extensions over
> +	 * all harts, to expose as AT_BASE_PLATFORM in the aux vector.
> +	 */
> +	isa_str = riscv_create_isa_string();
> +	if (!IS_ERR(isa_str))
> +		riscv_base_platform = isa_str;
> +
>  	return 0;
>  }
>  arch_initcall(riscv_cpuinfo_init);
> -- 
> 2.39.0
>

Otherwise,

Reviewed-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>