[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>

1 files changed, 65 insertions, 0 deletions

diff --git a/src/arch/i386/include/librm.h b/src/arch/i386/include/librm.h
index fc5598eb..4a4e61aa 100644
--- a/src/arch/i386/include/librm.h
+++ b/src/arch/i386/include/librm.h
@@ -209,6 +209,71 @@ extern void remove_user_from_rm_stack ( userptr_t data, size_t size );
 	asm_code_str					\
 	"call _phys_to_virt\n\t"
 
+/** Number of interrupts */
+#define NUM_INT 256
+
+/** An interrupt descriptor table register */
+struct idtr {
+	/** Limit */
+	uint16_t limit;
+	/** Base */
+	uint32_t base;
+} __attribute__ (( packed ));
+
+/** An interrupt descriptor table entry */
+struct interrupt_descriptor {
+	/** Low 16 bits of address */
+	uint16_t low;
+	/** Code segment */
+	uint16_t segment;
+	/** Unused */
+	uint8_t unused;
+	/** Type and attributes */
+	uint8_t attr;
+	/** High 16 bits of address */
+	uint16_t high;
+} __attribute__ (( packed ));
+
+/** Interrupt descriptor is present */
+#define IDTE_PRESENT 0x80
+
+/** Interrupt descriptor 32-bit interrupt gate type */
+#define IDTE_TYPE_IRQ32 0x0e
+
+/** An interrupt vector
+ *
+ * Each interrupt vector comprises an eight-byte fragment of code:
+ *
+ *   60			pushal
+ *   b0 xx		movb $INT, %al
+ *   e9 xx xx xx xx	jmp interrupt_wrapper
+ */
+struct interrupt_vector {
+	/** "pushal" instruction */
+	uint8_t pushal;
+	/** "movb" instruction */
+	uint8_t movb;
+	/** Interrupt number */
+	uint8_t intr;
+	/** "jmp" instruction */
+	uint8_t jmp;
+	/** Interrupt wrapper address offset */
+	uint32_t offset;
+	/** Next instruction after jump */
+	uint8_t next[0];
+} __attribute__ (( packed ));
+
+/** "pushal" instruction */
+#define PUSHAL_INSN 0x60
+
+/** "movb" instruction */
+#define MOVB_INSN 0xb0
+
+/** "jmp" instruction */
+#define JMP_INSN 0xe9
+
+extern void set_interrupt_vector ( unsigned int intr, void *vector );
+
 #endif /* ASSEMBLY */
 
 #endif /* LIBRM_H */