Re: [PATCH v3 08/14] target/ppc: Fix gen_sc to use correct nip

["Nicholas Piggin" <npiggin@gmail.com>]

On Fri Jun 16, 2023 at 9:03 AM AEST, BALATON Zoltan wrote:
> Most exceptions are raised with nip pointing to the faulting
> instruction but the sc instruction generating a syscall exception
> leaves nip pointing to next instruction. Fix gen_sc to not use
> gen_exception_err() which sets nip back but correctly set nip to
> pc_next so we don't have to patch this in the exception handlers.
>
> This changes the nip logged in dump_syscall and dump_hcall debug
> functions but now this matches how nip would be on a real CPU.

I think this is okay. I'll just send a possible scv change after
this goes in.

Reviewed-by: Nicholas Piggin <npiggin@gmail.com>

>
> Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
> ---
>  target/ppc/excp_helper.c | 39 ---------------------------------------
>  target/ppc/translate.c   |  8 +++++---
>  2 files changed, 5 insertions(+), 42 deletions(-)
>
> diff --git a/target/ppc/excp_helper.c b/target/ppc/excp_helper.c
> index f19a0f2d1d..903216c2a6 100644
> --- a/target/ppc/excp_helper.c
> +++ b/target/ppc/excp_helper.c
> @@ -495,12 +495,6 @@ static void powerpc_excp_40x(PowerPCCPU *cpu, int excp)
>          break;
>      case POWERPC_EXCP_SYSCALL:   /* System call exception                    */
>          dump_syscall(env);
> -
> -        /*
> -         * We need to correct the NIP which in this case is supposed
> -         * to point to the next instruction
> -         */
> -        env->nip += 4;
>          break;
>      case POWERPC_EXCP_FIT:       /* Fixed-interval timer interrupt           */
>          trace_ppc_excp_print("FIT");
> @@ -611,12 +605,6 @@ static void powerpc_excp_6xx(PowerPCCPU *cpu, int excp)
>          break;
>      case POWERPC_EXCP_SYSCALL:   /* System call exception                    */
>          dump_syscall(env);
> -
> -        /*
> -         * We need to correct the NIP which in this case is supposed
> -         * to point to the next instruction
> -         */
> -        env->nip += 4;
>          break;
>      case POWERPC_EXCP_FPU:       /* Floating-point unavailable exception     */
>      case POWERPC_EXCP_DECR:      /* Decrementer exception                    */
> @@ -759,13 +747,6 @@ static void powerpc_excp_7xx(PowerPCCPU *cpu, int excp)
>          } else {
>              dump_syscall(env);
>          }
> -
> -        /*
> -         * We need to correct the NIP which in this case is supposed
> -         * to point to the next instruction
> -         */
> -        env->nip += 4;
> -
>          /*
>           * The Virtual Open Firmware (VOF) relies on the 'sc 1'
>           * instruction to communicate with QEMU. The pegasos2 machine
> @@ -910,13 +891,6 @@ static void powerpc_excp_74xx(PowerPCCPU *cpu, int excp)
>          } else {
>              dump_syscall(env);
>          }
> -
> -        /*
> -         * We need to correct the NIP which in this case is supposed
> -         * to point to the next instruction
> -         */
> -        env->nip += 4;
> -
>          /*
>           * The Virtual Open Firmware (VOF) relies on the 'sc 1'
>           * instruction to communicate with QEMU. The pegasos2 machine
> @@ -1075,12 +1049,6 @@ static void powerpc_excp_booke(PowerPCCPU *cpu, int excp)
>          break;
>      case POWERPC_EXCP_SYSCALL:   /* System call exception                    */
>          dump_syscall(env);
> -
> -        /*
> -         * We need to correct the NIP which in this case is supposed
> -         * to point to the next instruction
> -         */
> -        env->nip += 4;
>          break;
>      case POWERPC_EXCP_FPU:       /* Floating-point unavailable exception     */
>      case POWERPC_EXCP_APU:       /* Auxiliary processor unavailable          */
> @@ -1322,13 +1290,6 @@ static void powerpc_excp_books(PowerPCCPU *cpu, int excp)
>          } else {
>              dump_syscall(env);
>          }
> -
> -        /*
> -         * We need to correct the NIP which in this case is supposed
> -         * to point to the next instruction
> -         */
> -        env->nip += 4;
> -
>          /* "PAPR mode" built-in hypercall emulation */
>          if (lev == 1 && books_vhyp_handles_hcall(cpu)) {
>              PPCVirtualHypervisorClass *vhc =
> diff --git a/target/ppc/translate.c b/target/ppc/translate.c
> index a32a9b8a5f..4260d3d66f 100644
> --- a/target/ppc/translate.c
> +++ b/target/ppc/translate.c
> @@ -4419,10 +4419,12 @@ static void gen_hrfid(DisasContext *ctx)
>  #endif
>  static void gen_sc(DisasContext *ctx)
>  {
> -    uint32_t lev;
> +    uint32_t lev = (ctx->opcode >> 5) & 0x7F;
>  
> -    lev = (ctx->opcode >> 5) & 0x7F;
> -    gen_exception_err(ctx, POWERPC_SYSCALL, lev);
> +    gen_update_nip(ctx, ctx->base.pc_next);
> +    gen_helper_raise_exception_err(cpu_env, tcg_constant_i32(POWERPC_SYSCALL),
> +                                   tcg_constant_i32(lev));
> +    ctx->base.is_jmp = DISAS_NORETURN;
>  }
>  
>  #if defined(TARGET_PPC64)
> -- 
> 2.30.9