[librm] Allow interrupts in protected mode

When running in a virtual machine, switching to real mode may be
expensive.  Allow interrupts to be enabled while in protected mode and
reflected down to the real-mode interrupt handlers.

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

src/arch/i386/core/gdbidt.S

@@ -1,101 +1,10 @@
 /*
- * Interrupt Descriptor Table (IDT) setup and interrupt handlers for GDB stub.
+ * Interrupt handlers for GDB stub
  */
 
-#include <librm.h>
-
 #define SIZEOF_I386_REGS	32
 #define SIZEOF_I386_FLAGS	4
 
-/****************************************************************************
- * Interrupt Descriptor Table
- ****************************************************************************
- */
-	.section ".data16", "aw", @progbits
-	.globl idtr
-idtr:
-idt_limit:
-	.word	idt_length - 1
-idt_base:
-	.long	0
-
-/* IDT entries have the following format:
- * offset_lo, segment selector, flags, offset_hi
- *
- * Since it is not possible to specify relocations in arbitrary
- * expressions like (int_overflow & 0xffff), we initialise the
- * IDT with entries in an incorrect format.
- *
- * The entries are shuffled into the correct format in init_librm().
- */
-#define IDT_ENTRY_EMPTY(name) .word 0, 0, 0, 0
-#define IDT_ENTRY_PRESENT(name) \
-	.long	int_##name; \
-	.word	0x8e00, VIRTUAL_CS
-
-.align 16
-idt:
-	IDT_ENTRY_PRESENT(divide_error)
-	IDT_ENTRY_PRESENT(debug_trap)
-	IDT_ENTRY_EMPTY(non_maskable_interrupt)
-	IDT_ENTRY_PRESENT(breakpoint)
-	IDT_ENTRY_PRESENT(overflow)
-	IDT_ENTRY_PRESENT(bound_range_exceeded)
-	IDT_ENTRY_PRESENT(invalid_opcode)
-	IDT_ENTRY_EMPTY(device_not_available)
-	IDT_ENTRY_PRESENT(double_fault)
-	IDT_ENTRY_EMPTY(coprocessor_segment_overrun)
-	IDT_ENTRY_PRESENT(invalid_tss)
-	IDT_ENTRY_PRESENT(segment_not_present)
-	IDT_ENTRY_PRESENT(stack_segment_fault)
-	IDT_ENTRY_PRESENT(general_protection)
-	IDT_ENTRY_PRESENT(page_fault)
-idt_end:
-	.equ	idt_length, idt_end - idt
-
-/* The IDT entries are fixed up (once) in init_librm() */
-idt_fixed:
-	.byte	0
-
-/****************************************************************************
- * idt_init (real-mode near call, 16-bit real-mode near return address)
- *
- * Initialise the IDT, called from init_librm.
- *
- * Parameters:
- *   %eax : IDT base address
- *
- * Destroys %ax, %bx, and %di.
- ****************************************************************************
- */
-	.section ".text16", "ax", @progbits
-	.code16
-	.globl idt_init
-idt_init:
-	movl	%eax, idt_base
-	addl	$idt, idt_base
-
-	/* IDT entries are only fixed up once */
-	movb	idt_fixed, %al
-	orb	%al, %al
-	jnz	2f
-	movb	$1, idt_fixed
-
-	/* Shuffle IDT entries into the correct format */
-	movb	$(idt_length / 8), %al
-	movw	$idt, %bx
-	or	%al, %al
-	jz	2f
-1:
-	movw	2(%bx), %di
-	xchg	%di, 6(%bx)
-	movw	%di, 2(%bx)
-	addw	$8, %bx
-	dec	%al
-	jnz	1b
-2:
-	ret
-
 /****************************************************************************
  * Interrupt handlers
  ****************************************************************************
@@ -111,35 +20,35 @@ idt_init:
 #define SIGSEGV 11
 #define SIGSTKFLT 16
 
-int_divide_error:
+	.globl	gdbmach_nocode_sigfpe
+gdbmach_nocode_sigfpe:
 	pushl	$SIGFPE
-	jmp	do_interrupt
+	jmp	gdbmach_interrupt
 
-int_debug_trap:
-int_breakpoint:
+	.globl	gdbmach_nocode_sigtrap
+gdbmach_nocode_sigtrap:
 	pushl	$SIGTRAP
-	jmp	do_interrupt
+	jmp	gdbmach_interrupt
 
-int_overflow:
-int_bound_range_exceeded:
+	.globl	gdbmach_nocode_sigstkflt
+gdbmach_nocode_sigstkflt:
 	pushl	$SIGSTKFLT
-	jmp	do_interrupt
+	jmp	gdbmach_interrupt
 
-int_invalid_opcode:
+	.globl	gdbmach_nocode_sigill
+gdbmach_nocode_sigill:
 	pushl	$SIGILL
-	jmp	do_interrupt
+	jmp	gdbmach_interrupt
 
-int_double_fault:
+	.globl	gdbmach_withcode_sigbus
+gdbmach_withcode_sigbus:
 	movl	$SIGBUS, (%esp)
-	jmp	do_interrupt
+	jmp	gdbmach_interrupt
 
-int_invalid_tss:
-int_segment_not_present:
-int_stack_segment_fault:
-int_general_protection:
-int_page_fault:
+	.globl	gdbmach_withcode_sigsegv
+gdbmach_withcode_sigsegv:
 	movl	$SIGSEGV, (%esp)
-	jmp	do_interrupt
+	jmp	gdbmach_interrupt
 
 /* When invoked, the stack contains: eflags, cs, eip, signo. */
 #define IH_OFFSET_GDB_REGS ( 0 )
@@ -161,7 +70,7 @@ int_page_fault:
 #define IH_OFFSET_FLUX_OLD_EFLAGS ( IH_OFFSET_OLD_EFLAGS - 40 )
 #define IH_OFFSET_FLUX_OLD_EIP ( IH_OFFSET_OLD_EIP - 36 )
 #define IH_OFFSET_FLUX_END ( IH_OFFSET_END - 20 )
-do_interrupt:
+gdbmach_interrupt:
 	/* Store CPU state in GDB register snapshot */
 	pushw	$0
 	pushw	%gs
@@ -187,25 +96,41 @@ do_interrupt:
 	pushl	%ecx
 	pushl	%eax
 
+	/* Switch to virtual addressing */
+	call	_intr_to_virt
+
 	/* Call GDB stub exception handler */
 	pushl	%esp
 	pushl	(IH_OFFSET_SIGNO + 4)(%esp)
 	call	gdbmach_handler
 	addl	$8, %esp
 
+	/* Copy register snapshot to new stack and switch to new stack */
+	movl	%esp, %esi
+	movl	(IH_OFFSET_GDB_SEG_REGS + 4)(%esp), %eax
+	movl	%eax, %es
+	movl	(IH_OFFSET_GDB_REGS + 16)(%esp), %edi
+	subl	$IH_OFFSET_END, %edi
+	movl	$(IH_OFFSET_END / 4), %ecx
+	pushl	%edi
+	ss rep movsl
+	popl	%edi
+	movl	%eax, %ss
+	movl	%edi, %esp
+
 	/* Restore CPU state from GDB register snapshot */
 	popl	%eax
 	popl	%ecx
 	popl	%edx
 	popl	%ebx
-	addl	$4, %esp /* Changing ESP currently not supported */
+	popl	%ebp /* Skip %esp: already loaded */
 	popl	%ebp
 	popl	%esi
 	popl	%edi
 	popl	IH_OFFSET_FLUX_OLD_EIP(%esp)
 	popl	IH_OFFSET_FLUX_OLD_EFLAGS(%esp)
 	popl	IH_OFFSET_FLUX_OLD_CS(%esp)
-	popl	%ss
+	popl	%ds /* Skip %ss: already loaded */
 	popl	%ds
 	popl	%es
 	popl	%fs