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

Anup Patel
2022-09-08T16:03:48Z

On Thu, Sep 8, 2022 at 9:19 PM Heiko Stübner <heiko@sntech.de> wrote:
>
> 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.

I can update the KVM RISC-V queue but I suggest to
use a smaller prefix. Maybe RV_xyz() ?

Regards,
Anup

>
>
>
>
> > +#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 */
> >