RISC-V: add infrastructure to allow different str* implementations
authorHeiko Stuebner <heiko.stuebner@vrull.eu>
Fri, 13 Jan 2023 21:23:00 +0000 (22:23 +0100)
committerPalmer Dabbelt <palmer@rivosinc.com>
Tue, 31 Jan 2023 19:43:23 +0000 (11:43 -0800)
commit56e0790c7f9e59ba6a0f4b59981d1d6fbf43efb0
tree8ce7a6332c962e62f84c6fcffc7faa88c31b617f
parent61a9b7129070e07c207d89fffbce577223507327
RISC-V: add infrastructure to allow different str* implementations

Depending on supported extensions on specific RISC-V cores,
optimized str* functions might make sense.

This adds basic infrastructure to allow patching the function calls
via alternatives later on.

The Linux kernel provides standard implementations for string functions
but when architectures want to extend them, they need to provide their
own.

The added generic string functions are done in assembler (taken from
disassembling the main-kernel functions for now) to allow us to control
the used registers and extend them with optimized variants.

This doesn't override the compiler's use of builtin replacements. So still
first of all the compiler will select if a builtin will be better suitable
i.e. for known strings. For all regular cases we will want to later
select possible optimized variants and in the worst case fall back to the
generic implemention added with this change.

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230113212301.3534711-2-heiko@sntech.de
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
arch/riscv/include/asm/string.h
arch/riscv/kernel/riscv_ksyms.c
arch/riscv/lib/Makefile
arch/riscv/lib/strcmp.S [new file with mode: 0644]
arch/riscv/lib/strlen.S [new file with mode: 0644]
arch/riscv/lib/strncmp.S [new file with mode: 0644]
arch/riscv/purgatory/Makefile