[PATCH] lib: sbi_misaligned_ldst: Add handling of C.LHU/C.LH and C.SH

[Anup Patel]

On Mon, Mar 4, 2024 at 11:50 AM Nylon Chen <nylon7717 at gmail.com> wrote:
>
> Anup Patel <apatel at ventanamicro.com> 於 2024年3月4日 週一 下午1:12寫道：
> >
> > On Mon, Feb 26, 2024 at 11:27 AM Nylon Chen <nylon.chen at sifive.com> wrote:
> > >
> > > From: "Nylon Chen" <nylon.chen at sifive.com>
> > >
> > > Added exception handling for compressed instructions C.LHU, C.LH, and
> > > C.SH from the zcb extension to the sbi_misaligned_ldst library.
> > >
> > > Signed-off-by: Nylon Chen <nylon.chen at sifive.com>
> > > ---
> > >  include/sbi/riscv_encoding.h  |  7 +++++++
> > >  lib/sbi/sbi_misaligned_ldst.c | 10 ++++++++++
> > >  2 files changed, 17 insertions(+)
> > >
> > > diff --git a/include/sbi/riscv_encoding.h b/include/sbi/riscv_encoding.h
> > > index e74cc0d..3d77e26 100644
> > > --- a/include/sbi/riscv_encoding.h
> > > +++ b/include/sbi/riscv_encoding.h
> > > @@ -837,6 +837,13 @@
> > >  #define INSN_MATCH_C_FSWSP             0xe002
> > >  #define INSN_MASK_C_FSWSP              0xe003
> > >
> > > +#define INSN_MATCH_C_LHU               0x8400
> > > +#define INSN_MASK_C_LHU                0xfc43
> > > +#define INSN_MATCH_C_LH                0x8440
> > > +#define INSN_MASK_C_LH                 0xfc43
> > > +#define INSN_MATCH_C_SH                0x8c00
> > > +#define INSN_MASK_C_SH                 0xfc43
> > > +
> > >  #define INSN_MASK_WFI                  0xffffff00
> > >  #define INSN_MATCH_WFI                 0x10500000
> > >
> > > diff --git a/lib/sbi/sbi_misaligned_ldst.c b/lib/sbi/sbi_misaligned_ldst.c
> > > index aa512de..9ca225a 100644
> > > --- a/lib/sbi/sbi_misaligned_ldst.c
> > > +++ b/lib/sbi/sbi_misaligned_ldst.c
> > > @@ -123,6 +123,13 @@ int sbi_misaligned_load_handler(ulong addr, ulong tval2, ulong tinst,
> > >                 len = 4;
> > >  #endif
> > >  #endif
> > > +       } else if ((insn & INSN_MASK_C_LHU) == INSN_MATCH_C_LHU) {
> > > +               len = 2;
> > > +               insn = RVC_RS2S(insn) << SH_RD;
> > > +       } else if ((insn & INSN_MASK_C_LH) == INSN_MATCH_C_LH) {
> > > +               len = 2;
> > > +               shift = 8 * (sizeof(ulong) - len);
> > > +               insn = RVC_RS2S(insn) << SH_RD;
> > >         } else {
> > >                 uptrap.epc = regs->mepc;
> > >                 uptrap.cause = CAUSE_MISALIGNED_LOAD;
> > > @@ -237,6 +244,9 @@ int sbi_misaligned_store_handler(ulong addr, ulong tval2, ulong tinst,
> > >                 val.data_ulong = GET_F32_RS2C(insn, regs);
> > >  #endif
> > >  #endif
> > > +       } else if ((insn & INSN_MASK_C_SH) == INSN_MATCH_C_SH) {
> > > +               len             = 2;
> > > +               val.data_ulong = GET_RS2S(insn, regs);
> >
> > Don't need to handle "c.sb" instruction ??
> Hi Anup, thanks for your feedback.
>
> in my opinion, because it's a byte so I don't think we'll encounter
> any misaligned issues.
>
> I also wrote the following test program to specifically test c.sb, and
> indeed, it doesn't require any exception handler.

Ahh, yes. We certainly don't need for the misaligned load/store handling.

There is a separate series from Bo Gan where we are re-purposing the
misaligned load/store handling for emulating load/store upon access
fault. I got mixed-up between two separate patches.

Regards,
Anup

>
> /* Check whether there is an address misalignment issue in the store
> byte instruction of zcb externsion. */
> void checkStoreB(unsigned char* memory, size_t offset, unsigned char
> value_byte) {
>     asm volatile (
>         "c.sb %[value_byte], 0(%[addr])"
>         :
>         : [value_byte] "r" (value_byte), [addr] "r" (memory + offset)
>         : "memory"
>     );
>
>     printf("Store (c.sb) operation at address: 0x%lx\n", (unsigned
> long)(memory + offset));
>
>     if (memcmp(memory + offset, &value_byte, sizeof(unsigned char)) == 0) {
>         printf("Store (c.sb) operation is correct: 0x%X\n", value_byte);
>     } else {
>         printf("Store (c.sb) operation may have address misalignment
> issues.\n");
>     }
> }
>
> int main() {
>     size_t size = 10;
>     unsigned char* memory = (unsigned char*)malloc(size);
>
>     if (memory == NULL) {
>         fprintf(stderr, "Memory allocation failed.\n");
>         return 1;
>     }
>
>     size_t offset = 1;
>
>     checkStoreB(memory, offset, 0x42);
> ...
> }
>
> >
> > >         } else {
> > >                 uptrap.epc = regs->mepc;
> > >                 uptrap.cause = CAUSE_MISALIGNED_STORE;
> > > --
> > > 2.34.1
> > >
> > >
> > > --
> > > opensbi mailing list
> > > opensbi at lists.infradead.org
> > > http://lists.infradead.org/mailman/listinfo/opensbi
> >
> > Regards,
> > Anup
>
>
>
> --
>
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