riscv: spike: allow base == 0

The sanity check on base doesn't allow htif to be mapped @0. Check if the
symbol exists instead so we can map it where we want.

Reviewed-by: Michael Clark <mjc@sifive.com>
Signed-off-by: KONRAD Frederic <frederic.konrad@adacore.com>
Signed-off-by: Michael Clark <mjc@sifive.com>

Message-Id: <1525360636-18229-2-git-send-email-frederic.konrad@adacore.com>
diff --git a/hw/riscv/riscv_htif.c b/hw/riscv/riscv_htif.c
index 3e17f30..be252ec 100644
--- a/hw/riscv/riscv_htif.c
+++ b/hw/riscv/riscv_htif.c
@@ -41,17 +41,20 @@
     } while (0)
 
 static uint64_t fromhost_addr, tohost_addr;
+static int address_symbol_set;
 
 void htif_symbol_callback(const char *st_name, int st_info, uint64_t st_value,
-    uint64_t st_size)
+                          uint64_t st_size)
 {
     if (strcmp("fromhost", st_name) == 0) {
+        address_symbol_set |= 1;
         fromhost_addr = st_value;
         if (st_size != 8) {
             error_report("HTIF fromhost must be 8 bytes");
             exit(1);
         }
     } else if (strcmp("tohost", st_name) == 0) {
+        address_symbol_set |= 2;
         tohost_addr = st_value;
         if (st_size != 8) {
             error_report("HTIF tohost must be 8 bytes");
@@ -248,7 +251,7 @@
     qemu_chr_fe_init(&s->chr, chr, &error_abort);
     qemu_chr_fe_set_handlers(&s->chr, htif_can_recv, htif_recv, htif_event,
         htif_be_change, s, NULL, true);
-    if (base) {
+    if (address_symbol_set == 3) {
         memory_region_init_io(&s->mmio, NULL, &htif_mm_ops, s,
                             TYPE_HTIF_UART, size);
         memory_region_add_subregion(address_space, base, &s->mmio);