[PATCH 0/5] target/alpha: Implement CF_PCREL

[PATCH 0/5] target/alpha: Implement CF_PCREL

[Richard Henderson]

Implement pc-relative tcg code generation.

r~

Richard Henderson (5):
  target/alpha: Use cpu_env in preference to ALPHA_CPU
  target/alpha: Hoist branch shift to initial decode
  target/alpha: Split out gen_goto_tb
  target/alpha: Split out gen_pc_disp
  target/alpha: Implement CF_PCREL

 target/alpha/cpu.c       |  32 ++++++++---
 target/alpha/helper.c    |   8 +--
 target/alpha/translate.c | 117 +++++++++++++++++++++------------------
 3 files changed, 91 insertions(+), 66 deletions(-)

-- 
2.34.1

[PATCH 1/5] target/alpha: Use cpu_env in preference to ALPHA_CPU

[Richard Henderson]

ALPHA_CPU has a dynamic object type assert, which is
unnecessary considering that these are all class hooks.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/alpha/cpu.c    | 15 ++++++---------
 target/alpha/helper.c |  8 ++++----
 2 files changed, 10 insertions(+), 13 deletions(-)

diff --git a/target/alpha/cpu.c b/target/alpha/cpu.c
index 05f9ee41e9..f98d022671 100644
--- a/target/alpha/cpu.c
+++ b/target/alpha/cpu.c
@@ -28,25 +28,22 @@
 
 static void alpha_cpu_set_pc(CPUState *cs, vaddr value)
 {
-    AlphaCPU *cpu = ALPHA_CPU(cs);
-
-    cpu->env.pc = value;
+    CPUAlphaState *env = cpu_env(cs);
+    env->pc = value;
 }
 
 static vaddr alpha_cpu_get_pc(CPUState *cs)
 {
-    AlphaCPU *cpu = ALPHA_CPU(cs);
-
-    return cpu->env.pc;
+    CPUAlphaState *env = cpu_env(cs);
+    return env->pc;
 }
 
 static void alpha_restore_state_to_opc(CPUState *cs,
                                        const TranslationBlock *tb,
                                        const uint64_t *data)
 {
-    AlphaCPU *cpu = ALPHA_CPU(cs);
-
-    cpu->env.pc = data[0];
+    CPUAlphaState *env = cpu_env(cs);
+    env->pc = data[0];
 }
 
 static bool alpha_cpu_has_work(CPUState *cs)
diff --git a/target/alpha/helper.c b/target/alpha/helper.c
index d6d4353edd..c5e4958f8b 100644
--- a/target/alpha/helper.c
+++ b/target/alpha/helper.c
@@ -124,7 +124,7 @@ void alpha_cpu_record_sigsegv(CPUState *cs, vaddr address,
                               MMUAccessType access_type,
                               bool maperr, uintptr_t retaddr)
 {
-    AlphaCPU *cpu = ALPHA_CPU(cs);
+    CPUAlphaState *env = cpu_env(cs);
     target_ulong mmcsr, cause;
 
     /* Assuming !maperr, infer the missing protection. */
@@ -155,9 +155,9 @@ void alpha_cpu_record_sigsegv(CPUState *cs, vaddr address,
     }
 
     /* Record the arguments that PALcode would give to the kernel. */
-    cpu->env.trap_arg0 = address;
-    cpu->env.trap_arg1 = mmcsr;
-    cpu->env.trap_arg2 = cause;
+    env->trap_arg0 = address;
+    env->trap_arg1 = mmcsr;
+    env->trap_arg2 = cause;
 }
 #else
 /* Returns the OSF/1 entMM failure indication, or -1 on success.  */
-- 
2.34.1

[PATCH 2/5] target/alpha: Hoist branch shift to initial decode

[Richard Henderson]

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/alpha/translate.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/target/alpha/translate.c b/target/alpha/translate.c
index a97cd54f0c..52c2e6248b 100644
--- a/target/alpha/translate.c
+++ b/target/alpha/translate.c
@@ -432,7 +432,7 @@ static bool use_goto_tb(DisasContext *ctx, uint64_t dest)
 
 static DisasJumpType gen_bdirect(DisasContext *ctx, int ra, int32_t disp)
 {
-    uint64_t dest = ctx->base.pc_next + (disp << 2);
+    uint64_t dest = ctx->base.pc_next + disp;
 
     if (ra != 31) {
         tcg_gen_movi_i64(ctx->ir[ra], ctx->base.pc_next);
@@ -455,7 +455,7 @@ static DisasJumpType gen_bdirect(DisasContext *ctx, int ra, int32_t disp)
 static DisasJumpType gen_bcond_internal(DisasContext *ctx, TCGCond cond,
                                         TCGv cmp, uint64_t imm, int32_t disp)
 {
-    uint64_t dest = ctx->base.pc_next + (disp << 2);
+    uint64_t dest = ctx->base.pc_next + disp;
     TCGLabel *lab_true = gen_new_label();
 
     if (use_goto_tb(ctx, dest)) {
@@ -1382,7 +1382,7 @@ static DisasJumpType translate_one(DisasContext *ctx, uint32_t insn)
     real_islit = islit = extract32(insn, 12, 1);
     lit = extract32(insn, 13, 8);
 
-    disp21 = sextract32(insn, 0, 21);
+    disp21 = sextract32(insn, 0, 21) * 4;
     disp16 = sextract32(insn, 0, 16);
     disp12 = sextract32(insn, 0, 12);
 
-- 
2.34.1

[PATCH 3/5] target/alpha: Split out gen_goto_tb

[Richard Henderson]

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/alpha/translate.c | 61 ++++++++++++++--------------------------
 1 file changed, 21 insertions(+), 40 deletions(-)

diff --git a/target/alpha/translate.c b/target/alpha/translate.c
index 52c2e6248b..c1a55e5153 100644
--- a/target/alpha/translate.c
+++ b/target/alpha/translate.c
@@ -425,60 +425,45 @@ static DisasJumpType gen_store_conditional(DisasContext *ctx, int ra, int rb,
     return DISAS_NEXT;
 }
 
-static bool use_goto_tb(DisasContext *ctx, uint64_t dest)
+static void gen_goto_tb(DisasContext *ctx, int idx, int32_t disp)
 {
-    return translator_use_goto_tb(&ctx->base, dest);
+    uint64_t dest = ctx->base.pc_next + disp;
+
+    if (translator_use_goto_tb(&ctx->base, dest)) {
+        tcg_gen_goto_tb(idx);
+        tcg_gen_movi_i64(cpu_pc, dest);
+        tcg_gen_exit_tb(ctx->base.tb, idx);
+    } else {
+        tcg_gen_movi_i64(cpu_pc, dest);
+        tcg_gen_lookup_and_goto_ptr();
+    }
 }
 
 static DisasJumpType gen_bdirect(DisasContext *ctx, int ra, int32_t disp)
 {
-    uint64_t dest = ctx->base.pc_next + disp;
-
     if (ra != 31) {
         tcg_gen_movi_i64(ctx->ir[ra], ctx->base.pc_next);
     }
 
     /* Notice branch-to-next; used to initialize RA with the PC.  */
     if (disp == 0) {
-        return 0;
-    } else if (use_goto_tb(ctx, dest)) {
-        tcg_gen_goto_tb(0);
-        tcg_gen_movi_i64(cpu_pc, dest);
-        tcg_gen_exit_tb(ctx->base.tb, 0);
-        return DISAS_NORETURN;
-    } else {
-        tcg_gen_movi_i64(cpu_pc, dest);
-        return DISAS_PC_UPDATED;
+        return DISAS_NEXT;
     }
+    gen_goto_tb(ctx, 0, disp);
+    return DISAS_NORETURN;
 }
 
 static DisasJumpType gen_bcond_internal(DisasContext *ctx, TCGCond cond,
                                         TCGv cmp, uint64_t imm, int32_t disp)
 {
-    uint64_t dest = ctx->base.pc_next + disp;
     TCGLabel *lab_true = gen_new_label();
 
-    if (use_goto_tb(ctx, dest)) {
-        tcg_gen_brcondi_i64(cond, cmp, imm, lab_true);
+    tcg_gen_brcondi_i64(cond, cmp, imm, lab_true);
+    gen_goto_tb(ctx, 0, 0);
+    gen_set_label(lab_true);
+    gen_goto_tb(ctx, 1, disp);
 
-        tcg_gen_goto_tb(0);
-        tcg_gen_movi_i64(cpu_pc, ctx->base.pc_next);
-        tcg_gen_exit_tb(ctx->base.tb, 0);
-
-        gen_set_label(lab_true);
-        tcg_gen_goto_tb(1);
-        tcg_gen_movi_i64(cpu_pc, dest);
-        tcg_gen_exit_tb(ctx->base.tb, 1);
-
-        return DISAS_NORETURN;
-    } else {
-        TCGv_i64 i = tcg_constant_i64(imm);
-        TCGv_i64 d = tcg_constant_i64(dest);
-        TCGv_i64 p = tcg_constant_i64(ctx->base.pc_next);
-
-        tcg_gen_movcond_i64(cond, cpu_pc, cmp, i, d, p);
-        return DISAS_PC_UPDATED;
-    }
+    return DISAS_NORETURN;
 }
 
 static DisasJumpType gen_bcond(DisasContext *ctx, TCGCond cond, int ra,
@@ -2920,12 +2905,8 @@ static void alpha_tr_tb_stop(DisasContextBase *dcbase, CPUState *cpu)
     case DISAS_NORETURN:
         break;
     case DISAS_TOO_MANY:
-        if (use_goto_tb(ctx, ctx->base.pc_next)) {
-            tcg_gen_goto_tb(0);
-            tcg_gen_movi_i64(cpu_pc, ctx->base.pc_next);
-            tcg_gen_exit_tb(ctx->base.tb, 0);
-        }
-        /* FALLTHRU */
+        gen_goto_tb(ctx, 0, 0);
+        break;
     case DISAS_PC_STALE:
         tcg_gen_movi_i64(cpu_pc, ctx->base.pc_next);
         /* FALLTHRU */
-- 
2.34.1

[PATCH 4/5] target/alpha: Split out gen_pc_disp

[Richard Henderson]

Prepare for pcrel by not modifying cpu_pc before use,
in the case of JSR.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/alpha/translate.c | 41 ++++++++++++++++++++++------------------
 1 file changed, 23 insertions(+), 18 deletions(-)

diff --git a/target/alpha/translate.c b/target/alpha/translate.c
index c1a55e5153..86402d96d5 100644
--- a/target/alpha/translate.c
+++ b/target/alpha/translate.c
@@ -252,6 +252,11 @@ static void st_flag_byte(TCGv val, unsigned shift)
     tcg_gen_st8_i64(val, tcg_env, get_flag_ofs(shift));
 }
 
+static void gen_pc_disp(DisasContext *ctx, TCGv dest, int32_t disp)
+{
+    tcg_gen_movi_i64(dest, ctx->base.pc_next + disp);
+}
+
 static void gen_excp_1(int exception, int error_code)
 {
     TCGv_i32 tmp1, tmp2;
@@ -263,7 +268,7 @@ static void gen_excp_1(int exception, int error_code)
 
 static DisasJumpType gen_excp(DisasContext *ctx, int exception, int error_code)
 {
-    tcg_gen_movi_i64(cpu_pc, ctx->base.pc_next);
+    gen_pc_disp(ctx, cpu_pc, 0);
     gen_excp_1(exception, error_code);
     return DISAS_NORETURN;
 }
@@ -427,14 +432,12 @@ static DisasJumpType gen_store_conditional(DisasContext *ctx, int ra, int rb,
 
 static void gen_goto_tb(DisasContext *ctx, int idx, int32_t disp)
 {
-    uint64_t dest = ctx->base.pc_next + disp;
-
-    if (translator_use_goto_tb(&ctx->base, dest)) {
+    if (translator_use_goto_tb(&ctx->base, ctx->base.pc_next + disp)) {
         tcg_gen_goto_tb(idx);
-        tcg_gen_movi_i64(cpu_pc, dest);
+        gen_pc_disp(ctx, cpu_pc, disp);
         tcg_gen_exit_tb(ctx->base.tb, idx);
     } else {
-        tcg_gen_movi_i64(cpu_pc, dest);
+        gen_pc_disp(ctx, cpu_pc, disp);
         tcg_gen_lookup_and_goto_ptr();
     }
 }
@@ -442,7 +445,7 @@ static void gen_goto_tb(DisasContext *ctx, int idx, int32_t disp)
 static DisasJumpType gen_bdirect(DisasContext *ctx, int ra, int32_t disp)
 {
     if (ra != 31) {
-        tcg_gen_movi_i64(ctx->ir[ra], ctx->base.pc_next);
+        gen_pc_disp(ctx, ctx->ir[ra], 0);
     }
 
     /* Notice branch-to-next; used to initialize RA with the PC.  */
@@ -1091,7 +1094,7 @@ static DisasJumpType gen_call_pal(DisasContext *ctx, int palcode)
             }
 
             /* Allow interrupts to be recognized right away.  */
-            tcg_gen_movi_i64(cpu_pc, ctx->base.pc_next);
+            gen_pc_disp(ctx, cpu_pc, 0);
             return DISAS_PC_UPDATED_NOCHAIN;
 
         case 0x36:
@@ -1138,19 +1141,17 @@ static DisasJumpType gen_call_pal(DisasContext *ctx, int palcode)
 #else
     {
         TCGv tmp = tcg_temp_new();
-        uint64_t exc_addr = ctx->base.pc_next;
-        uint64_t entry = ctx->palbr;
+        uint64_t entry;
 
+        gen_pc_disp(ctx, tmp, 0);
         if (ctx->tbflags & ENV_FLAG_PAL_MODE) {
-            exc_addr |= 1;
+            tcg_gen_ori_i64(tmp, tmp, 1);
         } else {
-            tcg_gen_movi_i64(tmp, 1);
-            st_flag_byte(tmp, ENV_FLAG_PAL_SHIFT);
+            st_flag_byte(tcg_constant_i64(1), ENV_FLAG_PAL_SHIFT);
         }
-
-        tcg_gen_movi_i64(tmp, exc_addr);
         tcg_gen_st_i64(tmp, tcg_env, offsetof(CPUAlphaState, exc_addr));
 
+        entry = ctx->palbr;
         entry += (palcode & 0x80
                   ? 0x2000 + (palcode - 0x80) * 64
                   : 0x1000 + palcode * 64);
@@ -2344,9 +2345,13 @@ static DisasJumpType translate_one(DisasContext *ctx, uint32_t insn)
         /* JMP, JSR, RET, JSR_COROUTINE.  These only differ by the branch
            prediction stack action, which of course we don't implement.  */
         vb = load_gpr(ctx, rb);
-        tcg_gen_andi_i64(cpu_pc, vb, ~3);
         if (ra != 31) {
-            tcg_gen_movi_i64(ctx->ir[ra], ctx->base.pc_next);
+            tmp = tcg_temp_new();
+            tcg_gen_andi_i64(tmp, vb, ~3);
+            gen_pc_disp(ctx, ctx->ir[ra], 0);
+            tcg_gen_mov_i64(cpu_pc, tmp);
+        } else {
+            tcg_gen_andi_i64(cpu_pc, vb, ~3);
         }
         ret = DISAS_PC_UPDATED;
         break;
@@ -2908,7 +2913,7 @@ static void alpha_tr_tb_stop(DisasContextBase *dcbase, CPUState *cpu)
         gen_goto_tb(ctx, 0, 0);
         break;
     case DISAS_PC_STALE:
-        tcg_gen_movi_i64(cpu_pc, ctx->base.pc_next);
+        gen_pc_disp(ctx, cpu_pc, 0);
         /* FALLTHRU */
     case DISAS_PC_UPDATED:
         tcg_gen_lookup_and_goto_ptr();
-- 
2.34.1

[PATCH 5/5] target/alpha: Implement CF_PCREL

[Richard Henderson]

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/alpha/cpu.c       | 23 ++++++++++++++++++++++-
 target/alpha/translate.c | 29 +++++++++++++++++++++++++----
 2 files changed, 47 insertions(+), 5 deletions(-)

diff --git a/target/alpha/cpu.c b/target/alpha/cpu.c
index f98d022671..0e2fbcb397 100644
--- a/target/alpha/cpu.c
+++ b/target/alpha/cpu.c
@@ -38,12 +38,27 @@ static vaddr alpha_cpu_get_pc(CPUState *cs)
     return env->pc;
 }
 
+static void alpha_cpu_synchronize_from_tb(CPUState *cs,
+                                          const TranslationBlock *tb)
+{
+    /* The program counter is always up to date with CF_PCREL. */
+    if (!(tb_cflags(tb) & CF_PCREL)) {
+        CPUAlphaState *env = cpu_env(cs);
+        env->pc = tb->pc;
+    }
+}
+
 static void alpha_restore_state_to_opc(CPUState *cs,
                                        const TranslationBlock *tb,
                                        const uint64_t *data)
 {
     CPUAlphaState *env = cpu_env(cs);
-    env->pc = data[0];
+
+    if (tb_cflags(tb) & CF_PCREL) {
+        env->pc = (env->pc & TARGET_PAGE_MASK) | data[0];
+    } else {
+        env->pc = data[0];
+    }
 }
 
 static bool alpha_cpu_has_work(CPUState *cs)
@@ -78,6 +93,11 @@ static void alpha_cpu_realizefn(DeviceState *dev, Error **errp)
     AlphaCPUClass *acc = ALPHA_CPU_GET_CLASS(dev);
     Error *local_err = NULL;
 
+#ifndef CONFIG_USER_ONLY
+    /* Use pc-relative instructions in system-mode */
+    cs->tcg_cflags |= CF_PCREL;
+#endif
+
     cpu_exec_realizefn(cs, &local_err);
     if (local_err != NULL) {
         error_propagate(errp, local_err);
@@ -190,6 +210,7 @@ static const struct SysemuCPUOps alpha_sysemu_ops = {
 
 static const TCGCPUOps alpha_tcg_ops = {
     .initialize = alpha_translate_init,
+    .synchronize_from_tb = alpha_cpu_synchronize_from_tb,
     .restore_state_to_opc = alpha_restore_state_to_opc,
 
 #ifdef CONFIG_USER_ONLY
diff --git a/target/alpha/translate.c b/target/alpha/translate.c
index 86402d96d5..db847e7a23 100644
--- a/target/alpha/translate.c
+++ b/target/alpha/translate.c
@@ -54,6 +54,9 @@ struct DisasContext {
     uint32_t tbflags;
     int mem_idx;
 
+    /* True if generating pc-relative code.  */
+    bool pcrel;
+
     /* implver and amask values for this CPU.  */
     int implver;
     int amask;
@@ -254,7 +257,12 @@ static void st_flag_byte(TCGv val, unsigned shift)
 
 static void gen_pc_disp(DisasContext *ctx, TCGv dest, int32_t disp)
 {
-    tcg_gen_movi_i64(dest, ctx->base.pc_next + disp);
+    uint64_t addr = ctx->base.pc_next + disp;
+    if (ctx->pcrel) {
+        tcg_gen_addi_i64(dest, cpu_pc, addr - ctx->base.pc_first);
+    } else {
+        tcg_gen_movi_i64(dest, addr);
+    }
 }
 
 static void gen_excp_1(int exception, int error_code)
@@ -433,8 +441,14 @@ static DisasJumpType gen_store_conditional(DisasContext *ctx, int ra, int rb,
 static void gen_goto_tb(DisasContext *ctx, int idx, int32_t disp)
 {
     if (translator_use_goto_tb(&ctx->base, ctx->base.pc_next + disp)) {
-        tcg_gen_goto_tb(idx);
-        gen_pc_disp(ctx, cpu_pc, disp);
+        /* With PCREL, PC must always be up-to-date. */
+        if (ctx->pcrel) {
+            gen_pc_disp(ctx, cpu_pc, disp);
+            tcg_gen_goto_tb(idx);
+        } else {
+            tcg_gen_goto_tb(idx);
+            gen_pc_disp(ctx, cpu_pc, disp);
+        }
         tcg_gen_exit_tb(ctx->base.tb, idx);
     } else {
         gen_pc_disp(ctx, cpu_pc, disp);
@@ -2852,6 +2866,7 @@ static void alpha_tr_init_disas_context(DisasContextBase *dcbase, CPUState *cpu)
 
     ctx->tbflags = ctx->base.tb->flags;
     ctx->mem_idx = alpha_env_mmu_index(env);
+    ctx->pcrel = ctx->base.tb->cflags & CF_PCREL;
     ctx->implver = env->implver;
     ctx->amask = env->amask;
 
@@ -2887,7 +2902,13 @@ static void alpha_tr_tb_start(DisasContextBase *db, CPUState *cpu)
 
 static void alpha_tr_insn_start(DisasContextBase *dcbase, CPUState *cpu)
 {
-    tcg_gen_insn_start(dcbase->pc_next);
+    DisasContext *ctx = container_of(dcbase, DisasContext, base);
+
+    if (ctx->pcrel) {
+        tcg_gen_insn_start(dcbase->pc_next & ~TARGET_PAGE_MASK);
+    } else {
+        tcg_gen_insn_start(dcbase->pc_next);
+    }
 }
 
 static void alpha_tr_translate_insn(DisasContextBase *dcbase, CPUState *cpu)
-- 
2.34.1

Re: [PATCH 1/5] target/alpha: Use cpu_env in preference to ALPHA_CPU

[Philippe Mathieu-Daudé]

On 25/4/24 01:44, Richard Henderson wrote:
> ALPHA_CPU has a dynamic object type assert, which is
> unnecessary considering that these are all class hooks.
> 
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>   target/alpha/cpu.c    | 15 ++++++---------
>   target/alpha/helper.c |  8 ++++----
>   2 files changed, 10 insertions(+), 13 deletions(-)

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

Re: [PATCH 2/5] target/alpha: Hoist branch shift to initial decode

[Philippe Mathieu-Daudé]

On 25/4/24 01:44, Richard Henderson wrote:
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>   target/alpha/translate.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

Re: [PATCH 4/5] target/alpha: Split out gen_pc_disp

[Philippe Mathieu-Daudé]

On 25/4/24 01:44, Richard Henderson wrote:
> Prepare for pcrel by not modifying cpu_pc before use,
> in the case of JSR.
> 
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>   target/alpha/translate.c | 41 ++++++++++++++++++++++------------------
>   1 file changed, 23 insertions(+), 18 deletions(-)

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

Re: [PATCH 3/5] target/alpha: Split out gen_goto_tb

[Philippe Mathieu-Daudé]

On 25/4/24 01:44, Richard Henderson wrote:
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>   target/alpha/translate.c | 61 ++++++++++++++--------------------------
>   1 file changed, 21 insertions(+), 40 deletions(-)


>   static DisasJumpType gen_bdirect(DisasContext *ctx, int ra, int32_t disp)
>   {

>       /* Notice branch-to-next; used to initialize RA with the PC.  */
>       if (disp == 0) {
> -        return 0;

This is the single case in the code base of returning a non-DISAS_foo
as DisasJumpType :)

> +        return DISAS_NEXT;
>       }

>   }

Re: [PATCH 3/5] target/alpha: Split out gen_goto_tb

[Richard Henderson]

On 4/29/24 09:58, Philippe Mathieu-Daudé wrote:
> On 25/4/24 01:44, Richard Henderson wrote:
>> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
>> ---
>>   target/alpha/translate.c | 61 ++++++++++++++--------------------------
>>   1 file changed, 21 insertions(+), 40 deletions(-)
> 
> 
>>   static DisasJumpType gen_bdirect(DisasContext *ctx, int ra, int32_t disp)
>>   {
> 
>>       /* Notice branch-to-next; used to initialize RA with the PC.  */
>>       if (disp == 0) {
>> -        return 0;
> 
> This is the single case in the code base of returning a non-DISAS_foo
> as DisasJumpType :)
> 
>> +        return DISAS_NEXT;

Yes.  Note that DISAS_NEXT == 0, so this worked accidentally.
But of course using the correct name is better.

r~