Re: [PATCH v3 01/33] target/ppc: Fix gen_sc to use correct nip

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

On Wed May 8, 2024 at 10:14 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.
>
> Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
> ---
>  target/ppc/excp_helper.c | 43 ++--------------------------------------
>  target/ppc/translate.c   | 15 ++++++--------
>  2 files changed, 8 insertions(+), 50 deletions(-)
>
> diff --git a/target/ppc/excp_helper.c b/target/ppc/excp_helper.c
> index 0712098cf7..92fe535815 100644
> --- a/target/ppc/excp_helper.c
> +++ b/target/ppc/excp_helper.c
> @@ -116,7 +116,7 @@ static void dump_syscall(CPUPPCState *env)
>                    ppc_dump_gpr(env, 0), ppc_dump_gpr(env, 3),
>                    ppc_dump_gpr(env, 4), ppc_dump_gpr(env, 5),
>                    ppc_dump_gpr(env, 6), ppc_dump_gpr(env, 7),
> -                  ppc_dump_gpr(env, 8), env->nip);
> +                  ppc_dump_gpr(env, 8), env->nip - 4);
>  }
>  
>  static void dump_hcall(CPUPPCState *env)
> @@ -131,7 +131,7 @@ static void dump_hcall(CPUPPCState *env)
>                    ppc_dump_gpr(env, 7), ppc_dump_gpr(env, 8),
>                    ppc_dump_gpr(env, 9), ppc_dump_gpr(env, 10),
>                    ppc_dump_gpr(env, 11), ppc_dump_gpr(env, 12),
> -                  env->nip);
> +                  env->nip - 4);
>  }
>  
>  #ifdef CONFIG_TCG
> @@ -516,12 +516,6 @@ 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");
> @@ -632,12 +626,6 @@ 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                    */
> @@ -780,13 +768,6 @@ 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
> @@ -932,13 +913,6 @@ 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
> @@ -1098,12 +1072,6 @@ 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          */
> @@ -1428,13 +1396,6 @@ 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 93ffec787c..e112c44a02 100644
> --- a/target/ppc/translate.c
> +++ b/target/ppc/translate.c
> @@ -4472,22 +4472,19 @@ static void gen_hrfid(DisasContext *ctx)
>  #endif
>  
>  /* sc */
> -#if defined(CONFIG_USER_ONLY)
> -#define POWERPC_SYSCALL POWERPC_EXCP_SYSCALL_USER
> -#else
> -#define POWERPC_SYSCALL POWERPC_EXCP_SYSCALL
> -#endif
>  static void gen_sc(DisasContext *ctx)
>  {
> -    uint32_t lev;
> -
>      /*
>       * LEV is a 7-bit field, but the top 6 bits are treated as a reserved
>       * field (i.e., ignored). ISA v3.1 changes that to 5 bits, but that is
>       * for Ultravisor which TCG does not support, so just ignore the top 6.
>       */
> -    lev = (ctx->opcode >> 5) & 0x1;
> -    gen_exception_err(ctx, POWERPC_SYSCALL, lev);
> +    uint32_t lev = (ctx->opcode >> 5) & 0x1;
> +#ifdef CONFIG_USER_ONLY
> +    gen_exception_err(ctx, POWERPC_EXCP_SYSCALL_USER, lev);
> +#else
> +    gen_exception_err_nip(ctx, POWERPC_EXCP_SYSCALL, lev, ctx->base.pc_next);
> +#endif

I think this is the nail in the coffin for this one. Let's shelve it.

Thanks,
Nick