target/mips: Use an exception for semihosting

Within do_interrupt, we hold the iothread lock, which
is required for Chardev access for the console, and for
the round trip for use_gdb_syscalls().

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

target/mips/tcg/sysemu/mips-semi.c

@@ -20,10 +20,10 @@
 #include "qemu/osdep.h"
 #include "cpu.h"
 #include "qemu/log.h"
-#include "exec/helper-proto.h"
 #include "semihosting/softmmu-uaccess.h"
 #include "semihosting/semihost.h"
 #include "semihosting/console.h"
+#include "internal.h"
 
 typedef enum UHIOp {
     UHI_exit = 1,
@@ -238,7 +238,7 @@ static int copy_argn_to_target(CPUMIPSState *env, int arg_num,
         unlock_user(p, gpr, 0);                 \
     } while (0)
 
-void helper_do_semihosting(CPUMIPSState *env)
+void mips_semihosting(CPUMIPSState *env)
 {
     target_ulong *gpr = env->active_tc.gpr;
     const UHIOp op = gpr[25];

target/mips/tcg/sysemu/tlb_helper.c

@@ -1053,6 +1053,10 @@ void mips_cpu_do_interrupt(CPUState *cs)
     }
     offset = 0x180;
     switch (cs->exception_index) {
+    case EXCP_SEMIHOST:
+        cs->exception_index = EXCP_NONE;
+        mips_semihosting(env);
+        return;
     case EXCP_DSS:
         env->CP0_Debug |= 1 << CP0DB_DSS;
         /*