semihosting: Implement SYS_TMPNAM

Part of Semihosting for AArch32 and AArch64 Release 2.0

Signed-off-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20210107170717.2098982-9-keithp@keithp.com>
Message-Id: <20210108224256.2321-20-alex.bennee@linaro.org>

hw/semihosting/arm-compat-semi.c

@@ -835,6 +835,7 @@ target_ulong do_common_semihosting(CPUState *cs)
     CPUArchState *env = cs->env_ptr;
     target_ulong args;
     target_ulong arg0, arg1, arg2, arg3;
+    target_ulong ul_ret;
     char * s;
     int nr;
     uint32_t ret;
@@ -998,8 +999,24 @@ target_ulong do_common_semihosting(CPUState *cs)
 
         return guestfd_fns[gf->type].flenfn(cs, gf);
     case TARGET_SYS_TMPNAM:
-        qemu_log_mask(LOG_UNIMP, "%s: SYS_TMPNAM not implemented", __func__);
-        return -1;
+        GET_ARG(0);
+        GET_ARG(1);
+        GET_ARG(2);
+        if (asprintf(&s, "/tmp/qemu-%x%02x", getpid(),
+                     (int) (arg1 & 0xff)) < 0) {
+            return -1;
+        }
+        ul_ret = (target_ulong) -1;
+
+        /* Make sure there's enough space in the buffer */
+        if (strlen(s) < arg2) {
+            char *output = lock_user(VERIFY_WRITE, arg0, arg2, 0);
+            strcpy(output, s);
+            unlock_user(output, arg0, arg2);
+            ul_ret = 0;
+        }
+        free(s);
+        return ul_ret;
     case TARGET_SYS_REMOVE:
         GET_ARG(0);
         GET_ARG(1);