On 12/05/2014 06:05 AM, Catalin Marinas wrote: > On Fri, Dec 05, 2014 at 10:39:40AM +0000, Arnd Bergmann wrote: >> On Thursday 04 December 2014 15:48:50 Olof Johansson wrote: >>> On Thu, Dec 4, 2014 at 3:41 PM, Alexander Graf <ag...@suse.de> wrote: >>>> On 04.12.14 22:15, Olof Johansson wrote: >>>>> On Thu, Dec 4, 2014 at 7:46 AM, Alexander Graf <ag...@suse.de> wrote: >>>>>> With binutils 2.25 the default alignment for 32bit arm sections changed >>>>>> to >>>>>> have everything 64k aligned. Armv7 binaries built with this binutils >>>>>> version >>>>>> run successfully on an arm64 system. >>>>>> >>>>>> Since effectively there is now the chance to run armv7 code on arm64 even >>>>>> with 64k page size, it doesn't make sense to block people from enabling >>>>>> CONFIG_COMPAT on those configurations. >>>>>> >>>>>> Signed-off-by: Alexander Graf <ag...@suse.de> >>>>>> --- >>>>>> arch/arm64/Kconfig | 1 - >>>>>> 1 file changed, 1 deletion(-) >>>>>> >>>>>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig >>>>>> index 9532f8d..3cf4f238 100644 >>>>>> --- a/arch/arm64/Kconfig >>>>>> +++ b/arch/arm64/Kconfig >>>>>> @@ -409,7 +409,6 @@ source "fs/Kconfig.binfmt" >>>>>> >>>>>> config COMPAT >>>>>> bool "Kernel support for 32-bit EL0" >>>>>> - depends on !ARM64_64K_PAGES >>>>>> select COMPAT_BINFMT_ELF >>>>>> select HAVE_UID16 >>>>>> select OLD_SIGSUSPEND3 >>>>> >>>>> This is hardly "compat". Sure, it's great to have a new binutils that >>>>> has larger alignment, but practically not a single existing binary >>>>> will work today if someone tries to do this. >>>> >>>> Yes, but IMHO that's an implementation detail. The same applies for >>>> 32bit PPC binaries if you use 4k aligned segments. If your applications >>>> are not aligned for your page size, you can't run them. The only >>>> platform that managed nevertheless FWIW was IA64 ;). >>> >>> Yes, but there the binutils change happened early enough that by the >>> time the kernel change went in, all major distros had binaries that >>> were compatible. >> >> What is the exact symptom you see when running an unaligned user >> space binary on 64k-pages? Do we at least print a helpful error >> message somewhere or does it just crash? > > The application doesn't even start because it cannot map page 0. It > looks like most 32-bit arm binaries are linked to be loaded at 32K.
I looked at this briefly and the first problem I narrowed in on was underflow in the calculation of the off variable in elf_map(). http://lxr.free-electrons.com/source/fs/binfmt_elf.c?v=3.18#L341 Chris -- Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
