[PATCH] lib: sbi_illegal_insn: Emulate c.li

[Xiang W]

在 2023-11-09星期四的 17:35 +0800，Inochi Amaoto写道：
> > The Linux kernel RISC-V image format allows that UEFI Images can also
> > be booted by non-UEFI firmware. However for that to work, the PE/Image
> > combo requires that 'MZ' is a valid instruction. On RISC-V, 'MZ' is
> > only a valid instruction if the hardware is C capable [1]. So add
> > Emulate c.li
> > 
> > Signed-off-by: Björn Töpel <bjorn at rivosinc.com>
> > Signed-off-by: Xiang W <wxjstz at 126.com>
> > ---
> > lib/sbi/sbi_illegal_insn.c | 18 +++++++++++++++++-
> > 1 file changed, 17 insertions(+), 1 deletion(-)
> > 
> > diff --git a/lib/sbi/sbi_illegal_insn.c b/lib/sbi/sbi_illegal_insn.c
> > index 2be4757..4ab10f4 100644
> > --- a/lib/sbi/sbi_illegal_insn.c
> > +++ b/lib/sbi/sbi_illegal_insn.c
> > @@ -102,6 +102,22 @@ static int system_opcode_insn(ulong insn, struct sbi_trap_regs *regs)
> > 	return 0;
> > }
> > 
> > +static int compressed_insn(ulong insn, struct sbi_trap_regs *regs) {
> > +	unsigned long imm, rd;
> > +	unsigned long *regs_p = (unsigned long *)regs;
> > +
> > +	if ((insn & 0xe003) == 0x4001) { /* c.li */
> > +		imm = (insn >> 2) & 0x1f;
> > +		imm |= ((insn >> 12) & 1) ? -32 : 0;
> > +		rd = (insn >> 7) & 0x1f;
> > +		if (rd)
> > +			regs_p[rd] = imm;
> > +		return 0;
> > +	}
> > +
> > +	return truly_illegal_insn(insn, regs);
> > +}
> > +
> > static const illegal_insn_func illegal_insn_table[32] = {
> > 	truly_illegal_insn, /* 0 */
> > 	truly_illegal_insn, /* 1 */
> > @@ -160,7 +176,7 @@ int sbi_illegal_insn_handler(ulong insn, struct sbi_trap_regs *regs)
> > 			return sbi_trap_redirect(regs, &uptrap);
> > 		}
> > 		if ((insn & 3) != 3)
> > -			return truly_illegal_insn(insn, regs);
> > +			return compressed_insn(insn, regs);
> > 	}
> > 
> > 	return illegal_insn_table[(insn & 0x7c) >> 2](insn, regs);
> > --
> > 2.42.0
> > 
> 
> I think this patch may be unnecessary.
> 
> After searching the boot flow of UEFI, I only found two implementations:
> 
> For QEMU RISC-V virt platform and SG2042 platform:
> SBI -> (SEC -> PEI -> DXE) -> bootloader -> OS
>                UEFI
> 
> For SiFive U540 platform:
> (SEC -> OpenSBI -> PEI -> DXE) -> bootloader -> OS
>              UEFI
> 
> Both invoke SBI at a very early stage and use raw vaild address, and
> handling the UEFI header is more like bootloader's job. I have no idea
> about why this should be handled by SBI. FYI, Björn Töpel.
This patch is used to solve the problem of non-UEFI firmware booting the
kernel. The UEFI boot kernel should parse the PE file header, so this
patch is not needed. But non-UEFI probably treats the kernel as a
binary image.

Regards,
Xiang W