On Aug 31, 2014, at 11:32 AM, Joel Sherrill <joel.sherr...@oarcorp.com> wrote:
>> Hi, >> >> I am writing some code and found that system crashed. I found it was >> unaligned access which causes `data abort` exception. I write a piece >> of code and objdump >> it. I am not sure this is right or not. >> >> command: >> arm-poky-linux-gnueabi-gcc -marm -mno-thumb-interwork -mabi=aapcs-linux >> -mword-relocations -march=armv7-a -mno-unaligned-access >> -ffunction-sections -fdata-sections -fno-common -ffixed-r9 -msoft-float >> -pipe -O2 -c 2.c -o 2.o >> >> arch is armv7-a and used '-mno-unaligned access' > > I think this is totally expected. You were passed a u8 pointer which is > aligned for that type (no restrictions likely). You cast it to a type with > stricter alignment requirements. The code is just flawed. Some CPUs handle > unaligned accesses but not your ARM. While armv7 and armv6 supports unaligned access, that support has to be enabled by the underlying O/S. Not knowing the underlying environment, I can't say whether that support is enabled. One issue we had in NetBSD in moving to gcc4.8 was that the NetBSD/arm kernel didn't enable unaligned access for armv[67] CPUs. We quickly changed things so unaligned access is supported.
