intel_adsp: bbzero/bmemcpy with picolibc fix

[teburd]

When building with picolibc and gcc, the loops to do zeroing/copying get replaced by gcc with calls to memset/memcpy. This fails this early in the boot process and results in an illegal instruction exception.

Marking the variables being manipulated in the calls as volatile prevents the compiler from optimizing the loops (replacing them with memset/memcpy).

Fixes #54224 for me

Signed-off-by: Tom Burdick thomas.burdick@intel.com

[teburd]

Removed volatile on the loop indexes as recommended by @keith-packard and verfied this still works on cavs25

[keith-packard]

In general, the compiler optimizations which replace hand-coded memory copy/clear patterns with calls to memcpy or memset can be prevented with the GCC -fno-tree-loop-distribute-patterns option. You can also prevent all optimizations that are based on C library semantics with -fno-builtin, although that's a big hammer. To prevent optimizations based on specific functions, you can use -fno-builtin-<function>, such as -fno-builtin-memcpy.

For this particular case, using volatile attributes on the pointers in the inline functions appears to generate fine code and will prevent replacement with inline functions as the type of the parameters isn't compatible (volatile uint32_t * vs void *).

Adding volatile to the index variables causes those to be allocated on the stack, which makes the code significantly longer (at least for my simple tests on x86_64).