On 28.11.17 03:09, Peng Fan wrote:
When compiling with android toolchain, there is an instruction "str q0, [x8],#16", but x8 is not 16bytes aligned, this instruction will trigger sync abort.
So, following Linux kernel, only use general regs for arm64. If not, compiler may use simd registers Q[x]. We need to avoid using simd registers in U-Boot, because load/store Q[x] has restriction that 128bits aligned when str/ldr.
Signed-off-by: Peng Fan peng.fan@nxp.com
The compiler should only output 16-byte-alignemnt-requiring instructions when it can safely assume that the variable in question is 16 byte aligned.
Where did x8 come from? That was probably just an unsafe cast?
For reference, I ran into something similar recently on 32bit ARM:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82445
And this indeed turned out to be a compiler bug.
FWIW the main reason Linux doesn't want to use FPU registers in kernel space is simply that it doesn't want to bother saving/restoring them on syscalls or interrupts. But I don't quite see why we would care in U-Boot.
Alex