[PATCH 5/7] RISC-V: fix auipc-jalr addresses in patched alternatives

[Heiko Stübner]

Am Dienstag, 15. November 2022, 15:28:27 CET schrieb Lad, Prabhakar:
> Hi Heiko,
> 
> Thank you for the patch.
> 
> On Thu, Nov 10, 2022 at 4:50 PM Heiko Stuebner <heiko at sntech.de> wrote:
> >
> > From: Heiko Stuebner <heiko.stuebner at vrull.eu>
> >
> > Alternatives live in a different section, so addresses used by call
> > functions will point to wrong locations after the patch got applied.
> >
> > Similar to arm64, adjust the location to consider that offset.
> >
> > Signed-off-by: Heiko Stuebner <heiko.stuebner at vrull.eu>
> > ---
> >  arch/riscv/kernel/cpufeature.c | 79 +++++++++++++++++++++++++++++++++-
> >  1 file changed, 77 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> > index 694267d1fe81..026512ca9c4c 100644
> > --- a/arch/riscv/kernel/cpufeature.c
> > +++ b/arch/riscv/kernel/cpufeature.c
> > @@ -298,6 +298,74 @@ static u32 __init_or_module cpufeature_probe(unsigned int stage)
> >         return cpu_req_feature;
> >  }
> >
> > +#include <asm/parse_asm.h>
> > +
> > +DECLARE_INSN(jalr, MATCH_JALR, MASK_JALR)
> > +DECLARE_INSN(auipc, MATCH_AUIPC, MASK_AUIPC)
> > +
> > +static inline bool is_auipc_jalr_pair(long insn1, long insn2)
> > +{
> > +       return is_auipc_insn(insn1) && is_jalr_insn(insn2);
> > +}
> > +
> > +#define JALR_SIGN_MASK         BIT(I_IMM_SIGN_OPOFF - I_IMM_11_0_OPOFF)
> > +#define JALR_OFFSET_MASK       I_IMM_11_0_MASK
> > +#define AUIPC_OFFSET_MASK      U_IMM_31_12_MASK
> > +#define AUIPC_PAD              (0x00001000)
> > +#define JALR_SHIFT             I_IMM_11_0_OPOFF
> > +
> > +#define to_jalr_imm(offset)                                            \
> > +       ((offset & I_IMM_11_0_MASK) << I_IMM_11_0_OPOFF)
> > +
> > +#define to_auipc_imm(offset)                                           \
> > +       ((offset & JALR_SIGN_MASK) ?                                    \
> > +       ((offset & AUIPC_OFFSET_MASK) + AUIPC_PAD) :    \
> > +       (offset & AUIPC_OFFSET_MASK))
> > +
> > +static void riscv_alternative_fix_auipc_jalr(unsigned int *alt_ptr,
> > +                                            unsigned int len, int patch_offset)
> > +{
> 
> I am yet to test this with my ASM code yet, but maybe can we move this
> to [0] so that other erratas can make use of it too?
> 
> [0] arch/riscv/kernel/patch.c

yeah, that sounds like a very good plan.

I also want to make the to_foo_imm macros shared.
I.e. right now they're just duplicated from the ftrace patching code.

Heiko