[U-Boot] [PATCH 1/4] x86: Specify -march=core2 to build 64-bit U-Boot proper

[Simon Glass]

On 10 October 2018 at 19:53, Bin Meng <bmeng.cn at gmail.com> wrote:
> With newer kernel.org GCC (7.3.0 or 8.1.0), the u-boot.rom image
> built for qemu-x86_64 target does not boot. It keeps resetting
> soon after the 32-bit SPL jumps to 64-bit proper. Debugging shows
> that the reset happens inside env_callback_init().
>
> 000000000113dd85 <env_callback_init>:
>  113dd85:       41 54                   push   %r12
>  113dd87:       55                      push   %rbp
>  113dd88:       31 c0                   xor    %eax,%eax
>  113dd8a:       53                      push   %rbx
>  113dd8b:       0f 57 c0                xorps  %xmm0,%xmm0
>
> Executing "xorps %xmm0,%xmm0" causes CPU to immediately reset.
> However older GCC like 5.4.0 (the one shipped by Ubuntu 16.04)
> does not generate such instructions that utilizes SSE for this
> function - env_callback_init() and U-Boot boots without any issue.
> Explicitly specifying -march=core2 for newer GCC allows U-Boot
> proper to boot again. Examine assembly codes of env_callback_init
> and there is no SSE instruction in that function hence U-Boot
> continues to boot.
>
> core2 seems to be the oldest arch in GCC that supports 64-bit.
> Like 32-bit U-Boot build we use -march=i386 which is the most
> conservative cpu type so that the image can run on any x86
> processor, let's do the same for the 64-bit U-Boot build.
>
> Signed-off-by: Bin Meng <bmeng.cn at gmail.com>
> ---
>
>  arch/x86/config.mk | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Simon Glass <sjg at chromium.org>