[U-Boot] [PATCH v2 02/14] x86: Ensure no instruction sets of MMX/SSE are generated in 64-bit build

[Simon Glass]

On 13 October 2018 at 21:52, Bin Meng <bmeng.cn at gmail.com> wrote:
> With the '-march=core2' fix, it seems that we have some luck that
> the 64-bit U-Boot boots again. However if we examine the disassembly
> codes there are still SSE instructions elsewhere which means passing
> cpu type to GCC is not enough to prevent it from generating these
> instructions. A simple test case is doing a 'bootefi selftest' from
> the U-Boot shell and it leads to a reset too.
>
> The 'bootefi selftest' reset is even seen with the image created by
> the relative older GCC 5.4.0, the one shipped by Ubuntu 16.04.
>
> The reset actually originates from undefined instruction exception
> caused by these SSE instructions. To keep U-Boot as a bootloader as
> simple as possible, we don't want to handle such advanced SIMD stuff.
> To make sure no MMX/SSE instruction sets are generated, tell GCC not
> to do this. Note AVX is out of the question as CORE2 is old enough
> to support AVX yet.
>
> Signed-off-by: Bin Meng <bmeng.cn at gmail.com>
> Reviewed-by: Heinrich Schuchardt <xypron.glpk at gmx.de>
> ---
>
> Changes in v2: None
>
>  arch/x86/config.mk | 1 +
>  1 file changed, 1 insertion(+)

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