From mboxrd@z Thu Jan 1 00:00:00 1970 From: arnd@arndb.de (Arnd Bergmann) Date: Thu, 18 Feb 2016 17:12:13 +0100 Subject: [PATCH 1/9] ARM: ARMv7-M uses BE-8, not BE-32 In-Reply-To: References: <1455804123-2526139-1-git-send-email-arnd@arndb.de> <1455804123-2526139-2-git-send-email-arnd@arndb.de> Message-ID: <2702301.CTWUiSsjZR@wuerfel> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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