target-xtensa: avoid double-stopping at breakpoints

env->exception_taken is set every time an exception is taken. It is used
to allow single-stepping to stop at the first exception handler
instruction. This however must exclude debug exceptions, as otherwise
first step from the instruction where breakpoint was hit stops at that
same instruction.
Also don't check env->exception_taken directly from the
gen_intermediate_code_internal, instead allocate and use TB flag
XTENSA_TBFLAG_EXCEPTION.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

target-xtensa/cpu.h

@@ -484,6 +484,7 @@ static inline int cpu_mmu_index(CPUXtensaState *env)
 #define XTENSA_TBFLAG_ICOUNT 0x20
 #define XTENSA_TBFLAG_CPENABLE_MASK 0x3fc0
 #define XTENSA_TBFLAG_CPENABLE_SHIFT 6
+#define XTENSA_TBFLAG_EXCEPTION 0x4000
 
 static inline void cpu_get_tb_cpu_state(CPUXtensaState *env, target_ulong *pc,
         target_ulong *cs_base, int *flags)
@@ -510,6 +511,9 @@ static inline void cpu_get_tb_cpu_state(CPUXtensaState *env, target_ulong *pc,
     if (xtensa_option_enabled(env->config, XTENSA_OPTION_COPROCESSOR)) {
         *flags |= env->sregs[CPENABLE] << XTENSA_TBFLAG_CPENABLE_SHIFT;
     }
+    if (ENV_GET_CPU(env)->singlestep_enabled && env->exception_taken) {
+        *flags |= XTENSA_TBFLAG_EXCEPTION;
+    }
 }
 
 #include "exec/cpu-all.h"

target-xtensa/op_helper.c

@@ -96,6 +96,9 @@ static void tb_invalidate_virtual_addr(CPUXtensaState *env, uint32_t vaddr)
 void HELPER(exception)(CPUXtensaState *env, uint32_t excp)
 {
     env->exception_index = excp;
+    if (excp == EXCP_DEBUG) {
+        env->exception_taken = 0;
+    }
     cpu_loop_exit(env);
 }
 

target-xtensa/translate.c

@@ -2918,8 +2918,7 @@ void gen_intermediate_code_internal(XtensaCPU *cpu,
 
     gen_tb_start();
 
-    if (cs->singlestep_enabled && env->exception_taken) {
-        env->exception_taken = 0;
+    if (tb->flags & XTENSA_TBFLAG_EXCEPTION) {
         tcg_gen_movi_i32(cpu_pc, dc.pc);
         gen_exception(&dc, EXCP_DEBUG);
     }