[PATCH] lib: sbi_illegal_insn: Emulate c.li

[Xiang W]

在 2023-11-09星期四的 19:20 +0800，Inochi Amaoto写道：
> > 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.
> 
> This is not a vaild scenario for UEFI binary. IIRC, even the aarch64 arch
> does not support using UEFI binary in this way. I agree with Jessica about
> the fact that they are different. If you insist, I suggest using a custom
> bootloader to handle this.
Now this modification only adds an instruction to simulate and will not affect
the other programs.

Regards,
Xiang W
> 
> > 
> > Regards,
> > Xiang W
> > 
> >