x86: 32 bit: interrupt stub consistency with 64 bit

Don't generate interrupt stubs for interrupt vectors below
FIRST_EXTERNAL_VECTOR, and make the table of interrupt vectors
(interrupt[]) __initconst.  Both of these changes both conserve memory
and improve consistency with 64 bits.
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

arch/x86/include/asm/hw_irq.h

@@ -110,7 +110,7 @@ extern asmlinkage void smp_invalidate_interrupt(struct pt_regs *);
 #endif
 
 #ifdef CONFIG_X86_32
-extern void (*const interrupt[NR_VECTORS])(void);
+extern void (*__initconst interrupt[NR_VECTORS-FIRST_EXTERNAL_VECTOR])(void);
 #endif
 
 typedef int vector_irq_t[NR_VECTORS];

arch/x86/kernel/entry_32.S

@@ -622,16 +622,16 @@ END(syscall_badsys)
  * Build the entry stubs and pointer table with
  * some assembler magic.
  */
-.section .rodata,"a"
+.section .init.rodata,"a"
 ENTRY(interrupt)
 .text
 
 ENTRY(irq_entries_start)
 	RING0_INT_FRAME
-vector=0
+vector=FIRST_EXTERNAL_VECTOR
 .rept NR_VECTORS
 	ALIGN
- .if vector
+ .if vector != FIRST_EXTERNAL_VECTOR
 	CFI_ADJUST_CFA_OFFSET -4
  .endif
 1:	pushl $~(vector)

arch/x86/kernel/irqinit_32.c

@@ -129,7 +129,7 @@ void __init native_init_IRQ(void)
 	for (i =  FIRST_EXTERNAL_VECTOR; i < NR_VECTORS; i++) {
 		/* SYSCALL_VECTOR was reserved in trap_init. */
 		if (i != SYSCALL_VECTOR)
-			set_intr_gate(i, interrupt[i]);
+			set_intr_gate(i, interrupt[i-FIRST_EXTERNAL_VECTOR]);
 	}
 
 

arch/x86/lguest/boot.c

@@ -590,7 +590,8 @@ static void __init lguest_init_IRQ(void)
 		 * a straightforward 1 to 1 mapping, so force that here. */
 		__get_cpu_var(vector_irq)[vector] = i;
 		if (vector != SYSCALL_VECTOR) {
-			set_intr_gate(vector, interrupt[vector]);
+			set_intr_gate(vector,
+				      interrupt[vector-FIRST_EXTERNAL_VECTOR]);
 			set_irq_chip_and_handler_name(i, &lguest_irq_controller,
 						      handle_level_irq,
 						      "level");