kernel: some boottime sanitychecks

. Check if we have the right number of boot modules
	. Check if the ELF parsing of VM actually succeeded

Both these are root causes of less-than-obvious other
errors/asserts a little further down the line; uncovered
while experimenting with booting by iPXE, specifically
(a) iPXE having a 8-multiboot-modules limit and
(b) trying to boot a gzipped VM.

include/minix/com.h

@@ -84,6 +84,7 @@
                                            computation in macros.*/
 #define INIT_PROC_NR ((endpoint_t) LAST_SPECIAL_PROC_NR)  /* init
                                                         -- goes multiuser */
+#define NR_BOOT_MODULES (INIT_PROC_NR+1)
 
 /* Root system process and root user process. */
 #define ROOT_SYS_PROC_NR  RS_PROC_NR

kernel/arch/i386/protect.c

@@ -419,7 +419,8 @@ void arch_boot_proc(struct boot_image *ip, struct proc *rp)
 		execi.clearproc = NULL;
 
 		/* parse VM ELF binary and alloc/map it into bootstrap pagetable */
-		libexec_load_elf(&execi);
+		if(libexec_load_elf(&execi) != OK)
+			panic("VM loading failed");
 
 	        /* Initialize the server stack pointer. Take it down three words
 		 * to give startup code something to use as "argc", "argv" and "envp".

kernel/main.c

@@ -143,6 +143,10 @@ void kmain(kinfo_t *local_cbi)
 
    proc_init();
 
+   if(NR_BOOT_MODULES != kinfo.mbi.mods_count)
+   	panic("expecting %d boot processes/modules, found %d",
+		NR_BOOT_MODULES, kinfo.mbi.mods_count);
+
   /* Set up proc table entries for processes in boot image. */
   for (i=0; i < NR_BOOT_PROCS; ++i) {
 	int schedulable_proc;