[comboot] Use built-in interrupt reflector

We now have the ability to handle interrupts while in protected mode,
and so no longer need to set up a dedicated interrupt descriptor table
while running COM32 executables.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/i386/image/com32.c

 #include <ipxe/init.h>
 #include <ipxe/io.h>
 
-struct idt_register com32_external_idtr = {
-	.limit = COM32_NUM_IDT_ENTRIES * sizeof ( struct idt_descriptor ) - 1,
-	.base = COM32_IDT
-};
-
-struct idt_register com32_internal_idtr;
-
 /**
  * Execute COMBOOT image
  *
 		unregister_image ( image );
 
 		__asm__ __volatile__ (
-			"sidt com32_internal_idtr\n\t"
-			"lidt com32_external_idtr\n\t"	       /* Set up IDT */
 			"movl %%esp, (com32_internal_esp)\n\t" /* Save internal virtual address space ESP */
 			"movl (com32_external_esp), %%esp\n\t" /* Switch to COM32 ESP (top of available memory) */
 			"call _virt_to_phys\n\t"               /* Switch to flat physical address space */
 			"pushl $6\n\t"                         /* Number of additional arguments */
 			"call *%6\n\t"                         /* Execute image */
 			"cli\n\t"			       /* Disable interrupts */
-			"call _phys_to_virt\n\t"	       /* Switch back to internal virtual address space */
-			"lidt com32_internal_idtr\n\t"	       /* Switch back to internal IDT (for debugging) */
+			"call _phys_to_virt\n\t"               /* Switch back to internal virtual address space */
 			"movl (com32_internal_esp), %%esp\n\t" /* Switch back to internal stack */
 		:
 		:
 
 
 /**
- * Load COM32 image into memory and set up the IDT
+ * Load COM32 image into memory
  * @v image		COM32 image
  * @ret rc		Return status code
  */
 static int com32_load_image ( struct image *image ) {
-	physaddr_t com32_irq_wrapper_phys;
-	struct idt_descriptor *idt;
-	struct ijb_entry *ijb;
 	size_t filesz, memsz;
 	userptr_t buffer;
-	int rc, i;
-
-	/* The interrupt descriptor table, interrupt jump buffer, and
-	 * image data are all contiguous in memory. Prepare them all at once.
-	 */
-	filesz = image->len +
-		COM32_NUM_IDT_ENTRIES * sizeof ( struct idt_descriptor ) +
-		COM32_NUM_IDT_ENTRIES * sizeof ( struct ijb_entry );
+	int rc;
+
+	filesz = image->len;
 	memsz = filesz;
-	buffer = phys_to_user ( COM32_IDT );
+	buffer = phys_to_user ( COM32_START_PHYS );
 	if ( ( rc = prep_segment ( buffer, filesz, memsz ) ) != 0 ) {
 		DBGC ( image, "COM32 %p: could not prepare segment: %s\n",
 		       image, strerror ( rc ) );
 		return rc;
 	}
 
-	/* Write the IDT and IJB */
-	idt = phys_to_virt ( COM32_IDT );
-	ijb = phys_to_virt ( COM32_IJB );
-	com32_irq_wrapper_phys = virt_to_phys ( com32_irq_wrapper );
-
-	for ( i = 0; i < COM32_NUM_IDT_ENTRIES; i++ ) {
-		uint32_t ijb_address = virt_to_phys ( &ijb[i] );
-
-		idt[i].offset_low = ijb_address & 0xFFFF;
-		idt[i].selector = PHYSICAL_CS;
-		idt[i].flags = IDT_INTERRUPT_GATE_FLAGS;
-		idt[i].offset_high = ijb_address >> 16;
-
-		ijb[i].pusha_instruction = IJB_PUSHA;
-		ijb[i].mov_instruction = IJB_MOV_AL_IMM8;
-		ijb[i].mov_value = i;
-		ijb[i].jump_instruction = IJB_JMP_REL32;
-		ijb[i].jump_destination = com32_irq_wrapper_phys -
-			virt_to_phys ( &ijb[i + 1] );
-	}
-
 	/* Copy image to segment */
-	buffer = phys_to_user ( COM32_START_PHYS );
 	memcpy_user ( buffer, 0, image->data, 0, filesz );
 
 	return 0;

src/arch/i386/include/comboot.h

 #include <setjmp.h>
 #include <ipxe/in.h>
 
-/** Descriptor in a 32-bit IDT */
-struct idt_descriptor {
-	uint16_t offset_low;
-	uint16_t selector;
-	uint16_t flags;
-	uint16_t offset_high;
-} __attribute__ (( packed ));
-
-/** Operand for the LIDT instruction */
-struct idt_register {
-	uint16_t limit;
-	uint32_t base;
-} __attribute__ (( packed ));
-
-/** Entry in the interrupt jump buffer */
-struct ijb_entry {
-	uint8_t pusha_instruction;
-	uint8_t mov_instruction;
-	uint8_t mov_value;
-	uint8_t jump_instruction;
-	uint32_t jump_destination;
-} __attribute__ (( packed ));
-
-/** The x86 opcode for "pushal" */
-#define IJB_PUSHA 0x60
-
-/** The x86 opcode for "movb $imm8,%al" */
-#define IJB_MOV_AL_IMM8 0xB0
-
-/** The x86 opcode for "jmp rel32" */
-#define IJB_JMP_REL32 0xE9
-
-/** Flags that specify a 32-bit interrupt gate with DPL=0 */
-#define IDT_INTERRUPT_GATE_FLAGS 0x8E00
-
-/** Address of COM32 interrupt descriptor table */
-#define COM32_IDT 0x100000
-
-/** Number of entries in a fully populated IDT */
-#define COM32_NUM_IDT_ENTRIES 256
-
-/** Address of COM32 interrupt jump buffer */
-#define COM32_IJB 0x100800
-
 /** Segment used for COMBOOT PSP and image */
 #define COMBOOT_PSP_SEG 0x07C0
 
 extern void com32_intcall_wrapper ( );
 extern void com32_farcall_wrapper ( );
 extern void com32_cfarcall_wrapper ( );
-extern void com32_irq_wrapper ( );
 
 /* Resolve a hostname to an (IPv4) address */
 extern int comboot_resolv ( const char *name, struct in_addr *address );

src/arch/i386/interface/syslinux/com32_call.c

 
 	return eax;
 }
-
-/**
- * IRQ handler
- */
-void __asmcall com32_irq ( uint32_t vector ) {
-	uint32_t *ivt_entry = phys_to_virt( vector * 4 );
-
-	__asm__ __volatile__ (
-		REAL_CODE ( "pushfw\n\t"
-			    "pushw %%cs\n\t"
-			    "pushw $com32_irq_return\n\t"
-			    "pushl %0\n\t"
-			    "lret\n"
-			    "com32_irq_return:\n\t" )
-		: /* no outputs */
-		: "r" ( *ivt_entry ) );
-}

src/arch/i386/interface/syslinux/com32_wrapper.S

 	.arch i386
 	.code32
 
-	/*
-	 * This code is entered after running the following sequence out of
-	 * the interrupt jump buffer:
-	 *
-	 * pushal
-	 * movb $vector, %al
-	 * jmp com32_irq_wrapper
-	 */
-
-	.globl com32_irq_wrapper
-com32_irq_wrapper:
-
-	movzbl %al,%eax
-	pushl %eax
-	movl $com32_irq, %eax
-	call com32_wrapper
-	popl %eax
-	popal
-	iret
-
 	.globl com32_farcall_wrapper
 com32_farcall_wrapper:
 
 	/* Switch to internal virtual address space */
 	call _phys_to_virt
 
-	/* Switch to internal IDT (if we have one for debugging) */
-	lidt com32_internal_idtr
-
 	mov %eax, (com32_helper_function)
 
 	/* Save external COM32 stack pointer */
 	movl %esp, (com32_internal_esp)
 	movl (com32_external_esp), %esp
 
-	/* Switch to com32 IDT */
-	lidt com32_external_idtr
-
 	/* Switch to external flat physical address space */
 	call _virt_to_phys