test_rom_cheri: expect a manifest on the 2nd-level firmware image

Change-Id: I48a4cef6ad15f3b7f882fa207a4aeaaab83d95d6

sw/device/lib/testing/test_rom/test_rom_cheri.c

diff --git a/sw/device/lib/testing/test_rom/test_rom_cheri.c b/sw/device/lib/testing/test_rom/test_rom_cheri.c
index d12d04f..2cdd308 100644
--- a/sw/device/lib/testing/test_rom/test_rom_cheri.c
+++ b/sw/device/lib/testing/test_rom/test_rom_cheri.c
@@ -275,8 +275,8 @@
   CHECK_DIF_OK(
       dif_flash_ctrl_set_exec_enablement(&flash_ctrl, kDifToggleEnabled));
 
-  // Always select slot A (NB: there is no hw address translation so ignore the
-  // manifest).
+  // Always select slot A (NB: there is no hw address translation so ignore any
+  // manifest setting).
   const manifest_t *manifest =
       (const manifest_t *)cderivecap(root_cap, TOP_MATCHA_EFLASH_BASE_ADDR,
                                      sizeof(manifest_t), CHERI_PERM_LOAD);
@@ -312,8 +312,10 @@
         (void *)get_mmio_ptr(root_cap, RAM_START, RAM_SIZE_BYTES),
         RAM_START + RAM_SIZE_BYTES);
     if (load_result == kDifOk) {
-      // TODO(sleffler): get entry point from manifest
-      entry_point = 0x10000000;
+      const manifest_t *manifest = (const manifest_t *)cderivecap(
+          root_cap, RAM_START, sizeof(manifest_t), CHERI_PERM_LOAD);
+      // Maybe vet with manifest_check?
+      entry_point = manifest_entry_point_get(manifest);
 #endif
     } else {
       LOG_FATAL("Failed to load program from SPI flash!");