[U-Boot] [PATCH] x86: Force 32-bit jumps in interrupt handlers

[Bin Meng]

On Fri, Feb 10, 2017 at 10:54 AM, J. Tang <tang at jtang.org> wrote:
> 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 at jtang.org>
> ---
>  arch/x86/cpu/i386/interrupt.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>

Reviewed-by: Bin Meng <bmeng.cn at gmail.com>