[PATCH v5 2/2] RISC-V: add zbb support to string functions

[Andrew Jones]

On Fri, Jan 13, 2023 at 10:23:01PM +0100, Heiko Stuebner wrote:
...
> diff --git a/arch/riscv/lib/strcmp.S b/arch/riscv/lib/strcmp.S
> index 8babd712b958..8148b6418f61 100644
> --- a/arch/riscv/lib/strcmp.S
> +++ b/arch/riscv/lib/strcmp.S
> @@ -3,9 +3,14 @@
>  #include <linux/linkage.h>
>  #include <asm/asm.h>
>  #include <asm-generic/export.h>
> +#include <asm/alternative-macros.h>
> +#include <asm/errata_list.h>
>  
>  /* int strcmp(const char *cs, const char *ct) */
>  SYM_FUNC_START(strcmp)
> +
> +	ALTERNATIVE("nop", "j strcmp_zbb", 0, CPUFEATURE_ZBB, CONFIG_RISCV_ISA_ZBB)
> +

I have something similar for Zicboz (which I've just reread as I'm
preparing v2). The difference is that I opted to penalize the non-
optimized version with the unconditional jump and give the optimized
version the nop. To do that here, it'd just need the label changed to
strcmp_basic or whatever, push the "basic" code down into it the new
label, and then put the new zbb code here.

Thanks,
drew