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

Andrew Jones
2022-09-08T16:55:53Z

On Thu, Sep 08, 2022 at 09:33:15PM +0530, Anup Patel wrote:
> 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() ?

Ack and thanks for doing the update.

drew

>
> 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 */
> > >
> >
> >
> >
> >