Re: [PATCH v3 15/23] target/mips: Extract break code into env->error_code

["Philippe Mathieu-Daudé" <f4bug@amsat.org>]

On 11/3/21 15:08, Richard Henderson wrote:
> Simplify cpu_loop by doing all of the decode in translate.
> 
> This fixes a bug in that cpu_loop was not handling the
> different layout of the R6 version of break16.  This fixes
> a bug in that cpu_loop extracted the wrong bits for the
> mips16e break16 instruction.
> 
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  target/mips/tcg/translate.h               |  1 +
>  linux-user/mips/cpu_loop.c                | 73 +++--------------------
>  target/mips/tcg/translate.c               | 12 +++-
>  target/mips/tcg/micromips_translate.c.inc |  6 +-
>  target/mips/tcg/mips16e_translate.c.inc   |  2 +-
>  5 files changed, 25 insertions(+), 69 deletions(-)

> diff --git a/linux-user/mips/cpu_loop.c b/linux-user/mips/cpu_loop.c
> index 034b31f853..8efb6d2a24 100644
> --- a/linux-user/mips/cpu_loop.c
> +++ b/linux-user/mips/cpu_loop.c
> @@ -65,6 +65,7 @@ void cpu_loop(CPUMIPSState *env)
>  {
>      CPUState *cs = env_cpu(env);
>      int trapnr, si_code;
> +    unsigned int code;
>      abi_long ret;
>  # ifdef TARGET_ABI_MIPSO32
>      unsigned int syscall_num;
> @@ -185,71 +186,15 @@ done_syscall:
>           * handling code in arch/mips/kernel/traps.c.
>           */
>          case EXCP_BREAK:
> -            {
> -                abi_ulong trap_instr;
> -                unsigned int code;
> -
> -                /*
> -                 * FIXME: It would be better to decode the trap number
> -                 * during translate, and store it in error_code while
> -                 * raising the exception.  We should not be re-reading
> -                 * the opcode here.
> -                 */
> -
> -                if (env->hflags & MIPS_HFLAG_M16) {
> -                    if (env->insn_flags & ASE_MICROMIPS) {
> -                        /* microMIPS mode */
> -                        ret = get_user_u16(trap_instr, env->active_tc.PC);
> -                        if (ret != 0) {
> -                            goto error;
> -                        }
> -
> -                        if ((trap_instr >> 10) == 0x11) {
> -                            /* 16-bit instruction */
> -                            code = trap_instr & 0xf;
> -                        } else {
> -                            /* 32-bit instruction */
> -                            abi_ulong instr_lo;
> -
> -                            ret = get_user_u16(instr_lo,
> -                                               env->active_tc.PC + 2);
> -                            if (ret != 0) {
> -                                goto error;
> -                            }
> -                            trap_instr = (trap_instr << 16) | instr_lo;
> -                            code = ((trap_instr >> 6) & ((1 << 20) - 1));
> -                            /* Unfortunately, microMIPS also suffers from
> -                               the old assembler bug...  */
> -                            if (code >= (1 << 10)) {
> -                                code >>= 10;
> -                            }
> -                        }
> -                    } else {
> -                        /* MIPS16e mode */
> -                        ret = get_user_u16(trap_instr, env->active_tc.PC);
> -                        if (ret != 0) {
> -                            goto error;
> -                        }
> -                        code = (trap_instr >> 6) & 0x3f;
> -                    }
> -                } else {
> -                    ret = get_user_u32(trap_instr, env->active_tc.PC);
> -                    if (ret != 0) {
> -                        goto error;
> -                    }
> -
> -                    /* As described in the original Linux kernel code, the
> -                     * below checks on 'code' are to work around an old
> -                     * assembly bug.
> -                     */
> -                    code = ((trap_instr >> 6) & ((1 << 20) - 1));
> -                    if (code >= (1 << 10)) {
> -                        code >>= 10;
> -                    }
> -                }
> -
> -                do_tr_or_bp(env, code, false);
> +            /*
> +             * As described in the original Linux kernel code, the below
> +             * checks on 'code' are to work around an old assembly bug.
> +             */
> +            code = env->error_code;
> +            if (code >= (1 << 10)) {
> +                code >>= 10;

Shouldn't we also move this to the translation (not in R6_BREAK16)?

>              }
> +            do_tr_or_bp(env, code, false);
>              break;
>          case EXCP_TRAP:
>              {
> diff --git a/target/mips/tcg/translate.c b/target/mips/tcg/translate.c
> index 47db35d7dd..a42f507aed 100644
> --- a/target/mips/tcg/translate.c
> +++ b/target/mips/tcg/translate.c
> @@ -1367,6 +1367,16 @@ void generate_exception_end(DisasContext *ctx, int excp)
>      generate_exception_err(ctx, excp, 0);
>  }
>  
> +void generate_exception_break(DisasContext *ctx, int code)
> +{
> +#ifdef CONFIG_USER_ONLY
> +    /* Pass the break code along to cpu_loop. */
> +    tcg_gen_st_i32(tcg_constant_i32(code), cpu_env,
> +                   offsetof(CPUMIPSState, error_code));
> +#endif
> +    generate_exception_end(ctx, EXCP_BREAK);
> +}
> +
>  void gen_reserved_instruction(DisasContext *ctx)
>  {
>      generate_exception_end(ctx, EXCP_RI);
> @@ -14160,7 +14170,7 @@ static void decode_opc_special(CPUMIPSState *env, DisasContext *ctx)
>          generate_exception_end(ctx, EXCP_SYSCALL);
>          break;
>      case OPC_BREAK:
> -        generate_exception_end(ctx, EXCP_BREAK);
> +        generate_exception_break(ctx, extract32(ctx->opcode, 6, 20));
>          break;
>      case OPC_SYNC:
>          check_insn(ctx, ISA_MIPS2);
> diff --git a/target/mips/tcg/micromips_translate.c.inc b/target/mips/tcg/micromips_translate.c.inc
> index 0da4c802a3..f91f7a96cd 100644
> --- a/target/mips/tcg/micromips_translate.c.inc
> +++ b/target/mips/tcg/micromips_translate.c.inc
> @@ -822,7 +822,7 @@ static void gen_pool16c_insn(DisasContext *ctx)
>          gen_HILO(ctx, OPC_MFLO, 0, uMIPS_RS5(ctx->opcode));
>          break;
>      case BREAK16:
> -        generate_exception_end(ctx, EXCP_BREAK);
> +        generate_exception_break(ctx, extract32(ctx->opcode, 0, 4));
>          break;
>      case SDBBP16:
>          if (is_uhi(extract32(ctx->opcode, 0, 4))) {
> @@ -937,7 +937,7 @@ static void gen_pool16c_r6_insn(DisasContext *ctx)
>              break;
>          case R6_BREAK16:
>              /* BREAK16 */
> -            generate_exception(ctx, EXCP_BREAK);
> +            generate_exception_break(ctx, extract32(ctx->opcode, 6, 4));
>              break;
>          case R6_SDBBP16:
>              /* SDBBP16 */
> @@ -1812,7 +1812,7 @@ static void decode_micromips32_opc(CPUMIPSState *env, DisasContext *ctx)
>              gen_pool32axf(env, ctx, rt, rs);
>              break;
>          case BREAK32:
> -            generate_exception_end(ctx, EXCP_BREAK);
> +            generate_exception_break(ctx, extract32(ctx->opcode, 6, 20));
>              break;
>          case SIGRIE:
>              check_insn(ctx, ISA_MIPS_R6);
> diff --git a/target/mips/tcg/mips16e_translate.c.inc b/target/mips/tcg/mips16e_translate.c.inc
> index 84d816603a..f57e0a5f2a 100644
> --- a/target/mips/tcg/mips16e_translate.c.inc
> +++ b/target/mips/tcg/mips16e_translate.c.inc
> @@ -969,7 +969,7 @@ static int decode_ase_mips16e(CPUMIPSState *env, DisasContext *ctx)
>              gen_slt(ctx, OPC_SLTU, 24, rx, ry);
>              break;
>          case RR_BREAK:
> -            generate_exception_end(ctx, EXCP_BREAK);
> +            generate_exception_break(ctx, extract32(ctx->opcode, 5, 6));
>              break;
>          case RR_SLLV:
>              gen_shift(ctx, OPC_SLLV, ry, rx, ry);
>