target/nios2: Create EXCP_SEMIHOST for semi-hosting

Decode 'break 1' during translation, rather than doing
it again during exception processing.

Reviewed-by: Peter Maydell <[email protected]>
Signed-off-by: Richard Henderson <[email protected]>
Message-Id: <[email protected]>
(cherry picked from commit 24ca313)

Author: rth7680

target/nios2/cpu.h

@@ -133,6 +133,7 @@ struct Nios2CPUClass {
 
 /* Exceptions */
 #define EXCP_BREAK    0x1000
+#define EXCP_SEMIHOST 0x1001
 #define EXCP_RESET    0
 #define EXCP_PRESET   1
 #define EXCP_IRQ      2

target/nios2/helper.c

@@ -171,14 +171,6 @@ void nios2_cpu_do_interrupt(CPUState *cs)
     case EXCP_BREAK:
         qemu_log_mask(CPU_LOG_INT, "BREAK exception at pc=%x\n",
                       env->regs[R_PC]);
-        /* The semihosting instruction is "break 1".  */
-        if (semihosting_enabled() &&
-            cpu_ldl_code(env, env->regs[R_PC]) == 0x003da07a)  {
-            qemu_log_mask(CPU_LOG_INT, "Entering semihosting\n");
-            env->regs[R_PC] += 4;
-            do_nios2_semihosting(env);
-            break;
-        }
 
         if ((env->regs[CR_STATUS] & CR_STATUS_EH) == 0) {
             env->regs[CR_BSTATUS] = env->regs[CR_STATUS];
@@ -194,6 +186,12 @@ void nios2_cpu_do_interrupt(CPUState *cs)
         env->regs[R_PC] = cpu->exception_addr;
         break;
 
+    case EXCP_SEMIHOST:
+        qemu_log_mask(CPU_LOG_INT, "BREAK semihosting at pc=%x\n", env->regs[R_PC]);
+        env->regs[R_PC] += 4;
+        do_nios2_semihosting(env);
+        break;
+
     default:
         cpu_abort(cs, "unhandled exception type=%d\n",
                   cs->exception_index);

target/nios2/translate.c

@@ -33,6 +33,7 @@
 #include "exec/translator.h"
 #include "qemu/qemu-print.h"
 #include "exec/gen-icount.h"
+#include "semihosting/semihost.h"
 
 /* is_jmp field values */
 #define DISAS_JUMP    DISAS_TARGET_0 /* only pc was modified dynamically */
@@ -644,6 +645,20 @@ static void trap(DisasContext *dc, uint32_t code, uint32_t flags)
     t_gen_helper_raise_exception(dc, EXCP_TRAP);
 }
 
+static void gen_break(DisasContext *dc, uint32_t code, uint32_t flags)
+{
+#ifndef CONFIG_USER_ONLY
+    /* The semihosting instruction is "break 1".  */
+    R_TYPE(instr, code);
+    if (semihosting_enabled() && instr.imm5 == 1) {
+        t_gen_helper_raise_exception(dc, EXCP_SEMIHOST);
+        return;
+    }
+#endif
+
+    t_gen_helper_raise_exception(dc, EXCP_BREAK);
+}
+
 static const Nios2Instruction r_type_instructions[] = {
     INSTRUCTION_ILLEGAL(),
     INSTRUCTION(eret),                                /* eret */
@@ -697,7 +712,7 @@ static const Nios2Instruction r_type_instructions[] = {
     INSTRUCTION(add),                                 /* add */
     INSTRUCTION_ILLEGAL(),
     INSTRUCTION_ILLEGAL(),
-    INSTRUCTION_FLG(gen_excp, EXCP_BREAK),            /* break */
+    INSTRUCTION(gen_break),                           /* break */
     INSTRUCTION_ILLEGAL(),
     INSTRUCTION(nop),                                 /* nop */
     INSTRUCTION_ILLEGAL(),