On 06/10/2012 05:31 PM, Michael Hope wrote: > There's an interaction between Linaro GCC or FSF GCC 4.7 and Linux > kernels before 3.2 which causes the kernel to halt straight after > showing 'Uncompressing Linux'. The question comes up every couple of > months so I've blogged about it: > http://seabright.co.nz/2012/06/11/kernel-not-booting-with-linaro-gcc/ > > """ > Is your ARM Linux kernel not booting when building with Linaro GCC or > FSF GCC 4.7? Does it halt shortly after showing ‘Uncompressing Linux’? > You may have run into an interaction between older kernels and the new > unaligned access support in GCC. This affects Linaro GCC from > 4.6-2011.11 onwards, GCC from 4.7.0 on, and kernels earlier than 3.2 > including the Galaxy Nexus Icecream Sandwich release. > > The work-around is to add -mno-unaligned-access to KBUILD_CFLAGS in > the top level kernel Makefile or to backport > 8428e84d42179c2a00f5f6450866e70d802d1d05 from the current kernel tree. > > ARMv6K and later processors have hardware support for doing unaligned > loads and stores which is faster than the old byte-by-byte/recombine > that was done in software. Later versions of GCC use this to do > quicker loads when working on known unaligned data, such as when > working on a protocol buffer or a packed structure. > > The CPU can be configured to trap on unaligned access. This trap is > off at reset, but pre 3.2 kernels turn this on during the initial > boot. An interaction between -fconserve-stack and -munaligned-access > on a char buffer lead to an unaligned access, which causes a trap, > which causes the kernel to halt. > > This does not affect userspace programs as they run with the trap turned off. > """
I've also hit this with u-boot if I enable armv7-a builds. Mainline u-boot generally builds using -march=armv5 and unaligned accesses disabled in h/w. Generally u-boot starts but dies on certain commands. I think there may be other u-boot issues with v7 compiles on newer gcc versions, but haven't debugged things further. Rob > > -- Michael > > _______________________________________________ > linaro-dev mailing list > linaro-dev@lists.linaro.org > http://lists.linaro.org/mailman/listinfo/linaro-dev _______________________________________________ linaro-dev mailing list linaro-dev@lists.linaro.org http://lists.linaro.org/mailman/listinfo/linaro-dev
