Re: [PATCH v2 2/4] riscv: Introduce support for defining instructions

Heiko Stübner
2022-09-08T15:53:29Z

Am Mittwoch, 31. August 2022, 19:24:58 CEST schrieb Andrew Jones:
> When compiling with toolchains that haven't yet been taught about
> new instructions we need to encode them ourselves. Create a new file
> where support for instruction definitions will evolve. We initiate
> the file with a macro called INSN_R(), which implements the R-type
> instruction encoding. INSN_R() will use the assembler's .insn
> directive when available, which should give the assembler a chance
> to do some validation. When .insn is not available we fall back to
> manual encoding.
>
> Not only should using instruction encoding macros improve readability
> and maintainability of code over the alternative of inserting
> instructions directly (e.g. '.word 0xc0de'), but we should also gain
> potential for more optimized code after compilation because the
> compiler will have control over the input and output registers used.
>
> Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
> Reviewed-by: Anup Patel <anup@brainfault.org>
> ---
> arch/riscv/Kconfig | 3 ++
> arch/riscv/include/asm/insn-def.h | 86 +++++++++++++++++++++++++++++++
> 2 files changed, 89 insertions(+)
> create mode 100644 arch/riscv/include/asm/insn-def.h
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index ed66c31e4655..f8f3b316b838 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -227,6 +227,9 @@ config RISCV_DMA_NONCOHERENT
> select ARCH_HAS_SETUP_DMA_OPS
> select DMA_DIRECT_REMAP
>
> +config AS_HAS_INSN
> + def_bool $(as-instr,.insn r 51$(comma) 0$(comma) 0$(comma) t0$(comma) t0$(comma) zero)
> +
> source "arch/riscv/Kconfig.socs"
> source "arch/riscv/Kconfig.erratas"
>
> diff --git a/arch/riscv/include/asm/insn-def.h b/arch/riscv/include/asm/insn-def.h
> new file mode 100644
> index 000000000000..2dcd1d4781bf
> --- /dev/null
> +++ b/arch/riscv/include/asm/insn-def.h
> @@ -0,0 +1,86 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +
> +#ifndef __ASM_INSN_DEF_H
> +#define __ASM_INSN_DEF_H
> +
> +#include <asm/asm.h>
> +
> +#define INSN_R_FUNC7_SHIFT 25
> +#define INSN_R_RS2_SHIFT 20
> +#define INSN_R_RS1_SHIFT 15
> +#define INSN_R_FUNC3_SHIFT 12
> +#define INSN_R_RD_SHIFT 7
> +#define INSN_R_OPCODE_SHIFT 0
> +
> +#ifdef __ASSEMBLY__
> +
> +#ifdef CONFIG_AS_HAS_INSN
> +
> + .macro insn_r, opcode, func3, func7, rd, rs1, rs2
> + .insn r \opcode, \func3, \func7, \rd, \rs1, \rs2
> + .endm
> +
> +#else
> +
> +#include <asm/gpr-num.h>
> +
> + .macro insn_r, opcode, func3, func7, rd, rs1, rs2
> + .4byte ((\opcode << INSN_R_OPCODE_SHIFT) | \
> + (\func3 << INSN_R_FUNC3_SHIFT) | \
> + (\func7 << INSN_R_FUNC7_SHIFT) | \
> + (.L__gpr_num_\rd << INSN_R_RD_SHIFT) | \
> + (.L__gpr_num_\rs1 << INSN_R_RS1_SHIFT) | \
> + (.L__gpr_num_\rs2 << INSN_R_RS2_SHIFT))
> + .endm
> +
> +#endif
> +
> +#define INSN_R(...) insn_r __VA_ARGS__
> +
> +#else /* ! __ASSEMBLY__ */
> +
> +#ifdef CONFIG_AS_HAS_INSN
> +
> +#define INSN_R(opcode, func3, func7, rd, rs1, rs2) \
> + ".insn r " opcode ", " func3 ", " func7 ", " rd ", " rs1 ", " rs2 "\n"
> +
> +#else
> +
> +#include <linux/stringify.h>
> +#include <asm/gpr-num.h>
> +
> +#define DEFINE_INSN_R \
> + __DEFINE_ASM_GPR_NUMS \
> +" .macro insn_r, opcode, func3, func7, rd, rs1, rs2\n" \
> +" .4byte ((\\opcode << " __stringify(INSN_R_OPCODE_SHIFT) ") |" \
> +" (\\func3 << " __stringify(INSN_R_FUNC3_SHIFT) ") |" \
> +" (\\func7 << " __stringify(INSN_R_FUNC7_SHIFT) ") |" \
> +" (.L__gpr_num_\\rd << " __stringify(INSN_R_RD_SHIFT) ") |" \
> +" (.L__gpr_num_\\rs1 << " __stringify(INSN_R_RS1_SHIFT) ") |" \
> +" (.L__gpr_num_\\rs2 << " __stringify(INSN_R_RS2_SHIFT) "))\n" \
> +" .endm\n"
> +
> +#define UNDEFINE_INSN_R \
> +" .purgem insn_r\n"
> +
> +#define INSN_R(opcode, func3, func7, rd, rs1, rs2) \
> + DEFINE_INSN_R \
> + "insn_r " opcode ", " func3 ", " func7 ", " rd ", " rs1 ", " rs2 "\n" \
> + UNDEFINE_INSN_R
> +
> +#endif
> +
> +#endif /* ! __ASSEMBLY__ */
> +
> +#define OPCODE(v) __ASM_STR(v)
> +#define FUNC3(v) __ASM_STR(v)
> +#define FUNC7(v) __ASM_STR(v)
> +#define RD(v) __ASM_STR(v)
> +#define RS1(v) __ASM_STR(v)
> +#define RS2(v) __ASM_STR(v)

you might want some sort of prefix here
RISCV_RS1(v) ?

While trying to adapt this for the cmo stuff I ran into the issue
of bpf complaining that "IMM" is already defined there.

And names above are generic enough that these also
might conflict with other stuff.

> +#define __REG(v) __ASM_STR(x ## v)
> +#define __RD(v) __REG(v)
> +#define __RS1(v) __REG(v)
> +#define __RS2(v) __REG(v)
> +
> +#endif /* __ASM_INSN_DEF_H */