[PATCH] x86_64: Add early exception handler

Add an early exception handler on x86-64 to get better debugging output for
crashes before traps_init. 

Requires earlyconsole.
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/x86_64/kernel/head.S

@@ -176,6 +176,18 @@ initial_code:
 init_rsp:
 	.quad  init_thread_union+THREAD_SIZE-8
 
+ENTRY(early_idt_handler)
+	xorl %eax,%eax
+	movq 8(%rsp),%rsi	# get rip
+	movq (%rsp),%rdx
+	movq %cr2,%rcx
+	leaq early_idt_msg(%rip),%rdi
+	call early_printk
+1:	hlt
+	jmp 1b
+
+early_idt_msg:
+	.asciz "PANIC: early exception rip %lx error %lx cr2 %lx\n"
 
 .code32
 ENTRY(no_long_mode)

arch/x86_64/kernel/head64.c

@@ -11,12 +11,14 @@
 #include <linux/types.h>
 #include <linux/kernel.h>
 #include <linux/string.h>
+#include <linux/percpu.h>
 
 #include <asm/processor.h>
 #include <asm/proto.h>
 #include <asm/smp.h>
 #include <asm/bootsetup.h>
 #include <asm/setup.h>
+#include <asm/desc.h>
 
 /* Don't add a printk in there. printk relies on the PDA which is not initialized 
    yet. */
@@ -79,7 +81,11 @@ extern char _end[];
 void __init x86_64_start_kernel(char * real_mode_data)
 {
 	char *s;
+	int i;
 
+	for (i = 0; i < 256; i++)
+		set_intr_gate(i, early_idt_handler);
+	asm volatile("lidt %0" :: "m" (idt_descr));
 	clear_bss();
 	pda_init(0);
 	copy_bootdata(real_mode_data);

include/asm-x86_64/desc.h

@@ -210,6 +210,8 @@ static inline void load_LDT(mm_context_t *pc)
 	put_cpu();
 }
 
+extern struct desc_ptr idt_descr;
+
 #endif /* !__ASSEMBLY__ */
 
 #endif

include/asm-x86_64/proto.h

@@ -12,6 +12,8 @@ extern void get_cpu_vendor(struct cpuinfo_x86*);
 extern void start_kernel(void);
 extern void pda_init(int); 
 
+extern void early_idt_handler(void);
+
 extern void mcheck_init(struct cpuinfo_x86 *c);
 extern void init_memory_mapping(void);