target/riscv: Honour -semihosting-config userspace=on and enable=on

The riscv target incorrectly enabled semihosting always, whether the
user asked for it or not.  Call semihosting_enabled() passing the
correct value to the is_userspace argument, which fixes this and also
handles the userspace=on argument.  Because we do this at translate
time, we no longer need to check the privilege level in
riscv_cpu_do_interrupt().

Note that this is a behaviour change: we used to default to
semihosting being enabled, and now the user must pass
"-semihosting-config enable=on" if they want it.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20220822141230.3658237-8-peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

target/riscv/cpu_helper.c

@@ -1589,12 +1589,9 @@ void riscv_cpu_do_interrupt(CPUState *cs)
     target_ulong mtval2 = 0;
 
     if  (cause == RISCV_EXCP_SEMIHOST) {
-        if (env->priv >= PRV_S) {
-            do_common_semihosting(cs);
-            env->pc += 4;
-            return;
-        }
-        cause = RISCV_EXCP_BREAKPOINT;
+        do_common_semihosting(cs);
+        env->pc += 4;
+        return;
     }
 
     if (!async) {

target/riscv/insn_trans/trans_privileged.c.inc

@@ -52,7 +52,8 @@ static bool trans_ebreak(DisasContext *ctx, arg_ebreak *a)
      * that no exception will be raised when fetching them.
      */
 
-    if ((pre_addr & TARGET_PAGE_MASK) == (post_addr & TARGET_PAGE_MASK)) {
+    if (semihosting_enabled(ctx->mem_idx < PRV_S) &&
+        (pre_addr & TARGET_PAGE_MASK) == (post_addr & TARGET_PAGE_MASK)) {
         pre    = opcode_at(&ctx->base, pre_addr);
         ebreak = opcode_at(&ctx->base, ebreak_addr);
         post   = opcode_at(&ctx->base, post_addr);

target/riscv/translate.c

@@ -28,6 +28,7 @@
 
 #include "exec/translator.h"
 #include "exec/log.h"
+#include "semihosting/semihost.h"
 
 #include "instmap.h"
 #include "internals.h"