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Date: Thu, 18 Feb 2016 17:12:13 +0100 From: Arnd Bergmann <arnd@...db.de> To: Nicolas Pitre <nicolas.pitre@...aro.org> Cc: Russell King <linux@....linux.org.uk>, linux-arm-kernel@...ts.infradead.org, Ard Biesheuvel <ard.biesheuvel@...aro.org>, Jon Medhurst <tixy@...aro.org>, Marc Zyngier <marc.zyngier@....com>, Linus Walleij <linus.walleij@...aro.org>, Maxime Coquelin stm32 <mcoquelin.stm32@...il.com>, linux-kernel@...r.kernel.org Subject: Re: [PATCH 1/9] ARM: ARMv7-M uses BE-8, not BE-32 On Thursday 18 February 2016 11:06:08 Nicolas Pitre wrote: > On Thu, 18 Feb 2016, Arnd Bergmann wrote: > > > 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. Arnd
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