x86: Force 32-bit jumps in interrupt handlers

x86: Force 32-bit jumps in interrupt handlers

Depending upon the compiler used, IRQ entries could vary in sizes. With
GCC 5.x, the code generator will use short jumps for some IRQ entries
but near jumps for others. For example, GCC 5.4.0 generates the
following:

$ objdump -d interrupt.o
<snip>
00000207 <irq_18>:
207:   6a 12                   push   $0x12
209:   eb 85                   jmp    190 <irq_common_entry>

0000020b <irq_19>:
20b:   6a 13                   push   $0x13
20d:   eb 81                   jmp    190 <irq_common_entry>

0000020f <irq_20>:
20f:   6a 14                   push   $0x14
211:   e9 7a ff ff ff          jmp    190 <irq_common_entry>

00000216 <irq_21>:
216:   6a 15                   push   $0x15
218:   e9 73 ff ff ff          jmp    190 <irq_common_entry>

This causes a problem in cpu_init_interrupts(), because the IDT setup
assumed same sizes for all IRQ entries. GCC 4.x always generated 32-bit
jumps, so this previously was not a problem.

The fix is to force 32-bit near jumps for all entries within the
inline assembly. This works for GCC 5.x, and 4.x was already using
that form of jumping.

Signed-off-by: Jason Tang <tang@jtang.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>