On Tue, 7 Jan 2020 at 17:18, Marc Glisse <marc.gli...@inria.fr> wrote:
>
> On Tue, 7 Jan 2020, Christophe Lyon wrote:
>
> > I've received a support request where GCC generates strd/ldrd which
> > require aligned memory addresses, while the user code actually
> > provides sub-aligned pointers.
> >
> > The sample code is derived from CMSIS:
> > #define __SIMD32_TYPE int
> > #define __SIMD32(addr) (*(__SIMD32_TYPE **) & (addr))
> >
> > void foo(short *pDst, int in1, int in2) {
> > *__SIMD32(pDst)++ = in1;
> > *__SIMD32(pDst)++ = in2;
> > }
> >
> > compiled with arm-none-eabi-gcc -mcpu=cortex-m7 CMSIS.c -S -O2
> > generates:
> > foo:
> > strd r1, r2, [r0]
> > bx lr
> >
> > Using -mno-unaligned-access of course makes no change, since the code
> > is lying to the compiler by casting short* to int*.
>
> If the issue is as well isolated as this, can't they just edit the code?
>
> typedef int __SIMD32_TYPE __attribute__((aligned(1)));
>
That type is defined by a macro in CMSIS's arm_math.h.
I think users don't want to play tricks with such libraries,
but I could try to check with them if something around these lines
would be acceptable.
> gets
>
> str r1, [r0] @ unaligned
> str r2, [r0, #4] @ unaligned
>
> instead of
>
> strd r1, r2, [r0]
>
> --
> Marc Glisse
