x86, kgdb: early trap init for early debug

Allow the x86 arch to have early exception processing for the purpose
of debugging via the kgdb.
Signed-off-by: NJan Kiszka <jan.kiszka@web.de>
Signed-off-by: NJason Wessel <jason.wessel@windriver.com>

arch/x86/include/asm/processor.h

@@ -789,6 +789,8 @@ static inline void wbinvd_halt(void)
 extern void enable_sep_cpu(void);
 extern int sysenter_setup(void);
 
+extern void early_trap_init(void);
+
 /* Defined in head.S */
 extern struct desc_ptr		early_gdt_descr;
 

arch/x86/kernel/setup.c

@@ -725,6 +725,7 @@ void __init setup_arch(char **cmdline_p)
 	/* VMI may relocate the fixmap; do this before touching ioremap area */
 	vmi_init();
 
+	early_trap_init();
 	early_cpu_init();
 	early_ioremap_init();
 

arch/x86/kernel/traps.c

@@ -808,6 +808,16 @@ dotraplinkage void do_iret_error(struct pt_regs *regs, long error_code)
 }
 #endif
 
+/* Set of traps needed for early debugging. */
+void __init early_trap_init(void)
+{
+	set_intr_gate_ist(1, &debug, DEBUG_STACK);
+	/* int3 can be called from all */
+	set_system_intr_gate_ist(3, &int3, DEBUG_STACK);
+	set_intr_gate(14, &page_fault);
+	load_idt(&idt_descr);
+}
+
 void __init trap_init(void)
 {
 	int i;
@@ -821,10 +831,7 @@ void __init trap_init(void)
 #endif
 
 	set_intr_gate(0, &divide_error);
-	set_intr_gate_ist(1, &debug, DEBUG_STACK);
 	set_intr_gate_ist(2, &nmi, NMI_STACK);
-	/* int3 can be called from all */
-	set_system_intr_gate_ist(3, &int3, DEBUG_STACK);
 	/* int4 can be called from all */
 	set_system_intr_gate(4, &overflow);
 	set_intr_gate(5, &bounds);
@@ -840,7 +847,6 @@ void __init trap_init(void)
 	set_intr_gate(11, &segment_not_present);
 	set_intr_gate_ist(12, &stack_segment, STACKFAULT_STACK);
 	set_intr_gate(13, &general_protection);
-	set_intr_gate(14, &page_fault);
 	set_intr_gate(15, &spurious_interrupt_bug);
 	set_intr_gate(16, &coprocessor_error);
 	set_intr_gate(17, &alignment_check);