[PATCH] Fix lguest bzImage loading with CONFIG_RELOCATABLE=y

[Rusty Russell <rusty@rustcorp.com.au>]

Jason Yeh sent his crashing .config: bzImages made with
CONFIG_RELOCATABLE=y put the relocs where the BSS is expected, and we
crash with unusual results such as:

	lguest: unhandled trap 14 at 0xc0122ae1 (0xa9)

Relying on BSS being zero was merely laziness on my part.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff -r cf2bfb364110 drivers/lguest/lguest.c
--- a/drivers/lguest/lguest.c	Fri Jul 27 13:04:22 2007 +1000
+++ b/drivers/lguest/lguest.c	Fri Jul 27 13:15:22 2007 +1000
@@ -1039,6 +1039,11 @@ __init void lguest_init(void *boot)
 	 * the normal data segment to get through booting. */
 	asm volatile ("mov %0, %%fs" : : "r" (__KERNEL_DS) : "memory");
 
+	/* Clear the part of the kernel data which is expected to be zero.
+	 * Normally it will be anyway, but if we're loading from a bzImage with
+	 * CONFIG_RELOCATALE=y, the relocations will be sitting here. */
+	memset(__bss_start, 0, __bss_stop - __bss_start);
+
 	/* The Host uses the top of the Guest's virtual address space for the
 	 * Host<->Guest Switcher, and it tells us how much it needs in
 	 * lguest_data.reserve_mem, set up on the LGUEST_INIT hypercall. */