On 09/02/2014 09:25 PM, Julian Brown wrote: > On Mon, 1 Sep 2014 09:14:31 +0800 > Peng Fan <van.free...@gmail.com> wrote: > >> On 09/01/2014 08:09 AM, Matt Thomas wrote: >>> >>> On Aug 31, 2014, at 11:32 AM, Joel Sherrill >>> <joel.sherr...@oarcorp.com> wrote: >>>> 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. >>> >> armv7 and armv6 arch except armv6-m support unaligned access. a u8 >> pointer is casted to u32 pointer, should gcc take the align problem >> into consideration to avoid possible errors? because >> -mno-unaligned-access. > > Using -munaligned-access (or its inverse) isn't enough to make GCC > generate code that can perform arbitrary unaligned accesses, because > several instructions (e.g. VFP loads/stores or load/store multiple > instructions IIRC) must still act on naturally-aligned data even when > the hardware flag to enable unaligned accesses is on, and those > instructions will still be generated by GCC when they are considered > safe, i.e. when not doing explicitly-unaligned accesses in packed > structures or similar. > > It would be *possible* to add an option to the backend to allow > arbitrary alignment for any access, I think, but it's not at all clear > that it's a good idea, and would certainly negatively affect > performance. > > (If you need unaligned accesses, you can use e.g. memcpy, and that will > probably generate good inline code.)
Thanks for the reply. I've tried memcpy and all is fine. Regards, Peng. > > Julian >
