DTB is placed to the end of memory, so we will check if the start
address of DTB overlaps to the address of kernel/initrd.

Signed-off-by: Jim Shu <jim.shu@sifive.com>
---
 hw/riscv/boot.c         | 25 ++++++++++++++++++++++++-
 include/hw/riscv/boot.h |  3 +++
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/hw/riscv/boot.c b/hw/riscv/boot.c
index 81d27f935e..bc8074fec8 100644
--- a/hw/riscv/boot.c
+++ b/hw/riscv/boot.c
@@ -70,6 +70,7 @@ char *riscv_plic_hart_config_string(int hart_count)
 void riscv_boot_info_init(RISCVBootInfo *info, RISCVHartArrayState *harts)
 {
     info->kernel_size = 0;
+    info->initrd_size = 0;
     info->is_32bit = riscv_is_32bit(harts);
 }
 
@@ -213,6 +214,9 @@ static void riscv_load_initrd(MachineState *machine, RISCVBootInfo *info)
         }
     }
 
+    info->initrd_start = start;
+    info->initrd_size = size;
+
     /* Some RISC-V machines (e.g. opentitan) don't have a fdt. */
     if (fdt) {
         end = start + size;
@@ -309,6 +313,7 @@ uint64_t riscv_compute_fdt_addr(hwaddr dram_base, hwaddr dram_size,
     int ret = fdt_pack(ms->fdt);
     hwaddr dram_end, temp;
     int fdtsize;
+    uint64_t dtb_start, dtb_start_limit;
 
     /* Should only fail if we've built a corrupted tree */
     g_assert(ret == 0);
@@ -319,6 +324,17 @@ uint64_t riscv_compute_fdt_addr(hwaddr dram_base, hwaddr dram_size,
         exit(1);
     }
 
+    if (info->initrd_size) {
+        /* If initrd is successfully loaded, place DTB after it. */
+        dtb_start_limit = info->initrd_start + info->initrd_size;
+    } else if (info->kernel_size) {
+        /* If only kernel is successfully loaded, place DTB after it. */
+        dtb_start_limit = info->image_high_addr;
+    } else {
+        /* Otherwise, do not check DTB overlapping */
+        dtb_start_limit = 0;
+    }
+
     /*
      * A dram_size == 0, usually from a MemMapEntry[].size element,
      * means that the DRAM block goes all the way to ms->ram_size.
@@ -338,7 +354,14 @@ uint64_t riscv_compute_fdt_addr(hwaddr dram_base, hwaddr dram_size,
         temp = (dram_base < 3072 * MiB) ? MIN(dram_end, 3072 * MiB) : dram_end;
     }
 
-    return QEMU_ALIGN_DOWN(temp - fdtsize, 2 * MiB);
+    dtb_start = QEMU_ALIGN_DOWN(temp - fdtsize, 2 * MiB);
+
+    if (dtb_start_limit && (dtb_start < dtb_start_limit)) {
+        error_report("No enough memory to place DTB after kernel/initrd");
+        exit(1);
+    }
+
+    return dtb_start;
 }
 
 /*
diff --git a/include/hw/riscv/boot.h b/include/hw/riscv/boot.h
index 06b51ed086..7d59b2e6c6 100644
--- a/include/hw/riscv/boot.h
+++ b/include/hw/riscv/boot.h
@@ -32,6 +32,9 @@ typedef struct RISCVBootInfo {
     hwaddr image_low_addr;
     hwaddr image_high_addr;
 
+    hwaddr initrd_start;
+    ssize_t initrd_size;
+
     bool is_32bit;
 } RISCVBootInfo;
 
-- 
2.17.1