core/init: Checksum romem after patching out traps

Currently we checksum the read-only parts of skiboot's memory just
before loading and booting petitboot. Commit 9ddc1a6
("core/util: trap based assertions") modifies the .text after this
point since it needs to disable the trap instructions that we use
to trigger an abort() before entering the kernel.

We can fix this by moving the checksum to after the point where the
traps are patched out. We could do the patching sooner, but since
load_and_boot_kernel() is a fairly complex function it's perferable
to keep boot-time assertion infrastructure active until just before
we enter the kernel.

Reported-by: Carol L Soto <clsoto@us.ibm.com>
Tested-by: Carol L Soto <clsoto@us.ibm.com>
Tested-by: Vasant Hegde <hegdevasant@linux.vnet.ibm.com>
Fixes: 9ddc1a6 ("core/util: trap based assertions")
Signed-off-by: Oliver O'Halloran <oohall@gmail.com>

core/init.c

@@ -85,6 +85,8 @@ struct debug_descriptor debug_descriptor = {
 #endif
 };
 
+static void checksum_romem(void);
+
 static bool try_load_elf64_le(struct elf_hdr *header)
 {
 	struct elf64_hdr *kh = (struct elf64_hdr *)header;
@@ -621,6 +623,8 @@ void __noreturn load_and_boot_kernel(bool is_reboot)
 
 	patch_traps(false);
 
+	checksum_romem();
+
 	debug_descriptor.state_flags |= OPAL_BOOT_COMPLETE;
 
 	cpu_give_self_os();
@@ -1320,8 +1324,6 @@ void __noreturn __nomcount main_cpu_entry(const void *fdt)
 
 	prd_register_reserved_memory();
 
-	checksum_romem();
-
 	load_and_boot_kernel(false);
 }