Re: [PATCH v4 11/12] RISC-V: add helpers for handling immediates in U-type and I-type pairs

["Heiko Stübner" <heiko@sntech.de>]

Am Donnerstag, 8. Dezember 2022, 15:38:11 CET schrieb Andrew Jones:
> On Wed, Dec 07, 2022 at 07:08:20PM +0100, Heiko Stuebner wrote:
> > From: Heiko Stuebner <heiko.stuebner@vrull.eu>
> > 
> > Used together U-type and I-type instructions can for example be used to
> > generate bigger jumps (i.e. in auipc+jalr pairs) by splitting the value
> > into an upper immediate (i.e. auipc) and a 12bit immediate (i.e. jalr).
> > 
> > Due to both immediates being considered signed this creates some corner
> > cases, so add some helper to prevent this from getting duplicated in
> > different places.
> > 
> > Signed-off-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
> > ---
> >  arch/riscv/include/asm/insn.h | 47 +++++++++++++++++++++++++++++++++++
> >  1 file changed, 47 insertions(+)
> > 
> > diff --git a/arch/riscv/include/asm/insn.h b/arch/riscv/include/asm/insn.h
> > index 2a23890b4577..bb1e6120a560 100644
> > --- a/arch/riscv/include/asm/insn.h
> > +++ b/arch/riscv/include/asm/insn.h
> > @@ -290,3 +290,50 @@ static __always_inline bool riscv_insn_is_branch(u32 code)
> >  	(RVC_X(x_, RVC_B_IMM_5_OPOFF, RVC_B_IMM_5_MASK) << RVC_B_IMM_5_OFF) | \
> >  	(RVC_X(x_, RVC_B_IMM_7_6_OPOFF, RVC_B_IMM_7_6_MASK) << RVC_B_IMM_7_6_OFF) | \
> >  	(RVC_IMM_SIGN(x_) << RVC_B_IMM_SIGN_OFF); })
> > +
> > +/*
> > + * Put together one immediate from a U-type and I-type instruction pair.
> > + *
> > + * The U-type contains an upper immediate, meaning bits[31:12] with [11:0]
> > + * being zero, while the I-type contains a 12bit immediate.
> > + * Combined these can encode larger 32bit values and are used for example
> > + * in auipc + jalr pairs to allow larger jumps.
> > + *
> > + * @utype_insn: instruction containing the upper immediate
> > + * @itype_insn: instruction
> > + * Return: combined immediate
> > + */
> > +static inline s32 riscv_insn_extract_utype_itype_imm(u32 utype_insn, u32 itype_insn)
> 
> Might be nice to keep the interfaces of these two complementing functions
> consistent by taking a u32 *insn here, like below. Or, below, taking
> &utype_insn and &itype_insn, like here.

I did go with separating the instructions in the insert function, simply
because I think it's way nicer to not impose the fixed structure
(2 u32 array) on every possible caller .

Heiko



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