[PATCH 3/3] target/m68k: Support semihosting on non-ColdFire targets

[Keith Packard]

According to the m68k semihosting spec:

"The instruction used to trigger a semihosting request depends on the
 m68k processor variant.  On ColdFire, "halt" is used; on other processors
 (which don't implement "halt"), "bkpt #0" may be used."

Add support for non-CodeFire processors by matching BKPT #0
instructions. When semihosting is disabled, convert those
back to illegal op exceptions.

Signed-off-by: Keith Packard <keithp@keithp.com>
---
 target/m68k/cpu.h       |  1 +
 target/m68k/op_helper.c | 16 ++++++++++++++++
 target/m68k/translate.c |  4 ++++
 3 files changed, 21 insertions(+)

diff --git a/target/m68k/cpu.h b/target/m68k/cpu.h
index cf70282717..b741c50a8f 100644
--- a/target/m68k/cpu.h
+++ b/target/m68k/cpu.h
@@ -67,6 +67,7 @@
 
 #define EXCP_RTE            0x100
 #define EXCP_HALT_INSN      0x101
+#define EXCP_BKPT_INSN      0x102
 
 #define M68K_DTTR0   0
 #define M68K_DTTR1   1
diff --git a/target/m68k/op_helper.c b/target/m68k/op_helper.c
index 1ce850bbc5..2d89db6dde 100644
--- a/target/m68k/op_helper.c
+++ b/target/m68k/op_helper.c
@@ -295,6 +295,22 @@ static void m68k_interrupt_all(CPUM68KState *env, int 
is_hw)
             /* Return from an exception.  */
             m68k_rte(env);
             return;
+        case EXCP_BKPT_INSN:
+            if (semihosting_enabled((env->sr & SR_S) == 0)
+                    && (env->pc & 3) == 0
+                    && cpu_lduw_code(env, env->pc - 4) == 0x4e71
+                    && cpu_ldl_code(env, env->pc) == 0x4e7bf000) {
+                env->pc += 4;
+                do_m68k_semihosting(env, env->dregs[0]);
+                return;
+            }
+            /*
+             * When semihosting is not enabled, translate this back to
+             * an illegal op exception.
+             */
+            cs->exception_index = EXCP_ILLEGAL;
+            env->pc += 2;
+            break;
         }
     }
 
diff --git a/target/m68k/translate.c b/target/m68k/translate.c
index e07161d76f..d037c57453 100644
--- a/target/m68k/translate.c
+++ b/target/m68k/translate.c
@@ -2640,6 +2640,10 @@ DISAS_INSN(bkpt)
 #if defined(CONFIG_USER_ONLY)
     gen_exception(s, s->base.pc_next, EXCP_DEBUG);
 #else
+    if ((insn & 7) == 0) {
+        gen_exception(s, s->pc, EXCP_BKPT_INSN);
+        return;
+    }
     gen_exception(s, s->base.pc_next, EXCP_ILLEGAL);
 #endif
 }
-- 
2.40.1