On 18/02/16 16:12, Arnd Bergmann wrote:

On Thursday 18 February 2016 11:06:08 Nicolas Pitre wrote:

quoted

On Thu, 18 Feb 2016, Arnd Bergmann wrote:

quoted

When configuring the kernel for big-endian, we set either BE-8 or BE-32
based on the CPU architecture level. Until linux-4.4, we did not have
any ARMv7-M platform allowing big-endian builds, but now i.MX/Vybrid
is in that category, adn we get a build error because of this:

arch/arm/kernel/module-plts.c: In function 'get_module_plt':
arch/arm/kernel/module-plts.c:60:46: error: implicit declaration of function '__opcode_to_mem_thumb32' [-Werror=implicit-function-declaration]

This comes down to picking the wrong default, ARMv7-M uses BE8
like ARMv7-A does. Changing the default gets the kernel to compile
and presumably works.

Was it tested without BE8 when it was submitted upstream? I don't think 
you can switch this freely on a given hardware platform and expect it to 
still work.

mach-imx contains a number of different SoCs, and one SoC was recently
tested successfully after a number of endianess bugs got fixed. This was
an i.mx6 using a Cortex-A9 core, but we are now also able to build
vybrid vf610 big-endian based on that selection. This SoC supports
Linux running either on its Cortex-A5 or its Cortex-M3 (or M4?) cores.

I am rather sure nobody has ever run Linux in big-endian mode on the
Cortex-M platform, specifically because it was always wrong and could
not be enabled in Kconfig.

Ah, it explains why my quick attempt to enable BE for MPS2 (M-class
platform) failed. With this patch applied I'm able to see Linux booting
on MPS2 FVP model in BE, not complete boot but it might be due to other
reasons. So this patch definitely improves things for me, if it helps

Tested-by: Vladimir Murzin <redacted>

Cheers
Vladimir

	Arnd

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