altos/arm: Align data so that gcc 5.4 doesn't do byte-accesses. Add -Wcast-align

Gcc 5.4.1 tracks alignment of data through assignments, so that a
uint32_t pointer which comes from byte-aligned uint8_t data:

extern uint8_t foo[];

	uint32_t	*q = (void *) foo;

Fetches and stores through this pointer are done bytewise. This is
slow (meh), but if q references a device register, things to bad very
quickly.

This patch works around this bug in the compiler by adding
__attribute__((aligned(4))) tags to some variables, or changing them
from uint8_t to uint32_t. Places doing this will now be caught as I've
added -Wcast-align to the compiler flags. That required adding (void
*) casts, after the relevant code was checked to make sure the
compiler could tell that the addresses were aligned.

Signed-off-by: Keith Packard <keithp@keithp.com>

1 files changed, 2 insertions, 7 deletions

diff --git a/src/stm/ao_arch_funcs.h b/src/stm/ao_arch_funcs.h
index 18ca20da..a9d0fa34 100644
--- a/src/stm/ao_arch_funcs.h
+++ b/src/stm/ao_arch_funcs.h
@@ -375,7 +375,7 @@ ao_arch_irq_check(void) {
 static inline void
 ao_arch_init_stack(struct ao_task *task, void *start)
 {
-	uint32_t	*sp = (uint32_t *) (task->stack + AO_STACK_SIZE);
+	uint32_t	*sp = (uint32_t *) ((void*) task->stack + AO_STACK_SIZE);
 	uint32_t	a = (uint32_t) start;
 	int		i;
 
@@ -413,16 +413,11 @@ static inline void ao_arch_save_stack(void) {
 	uint32_t	*sp;
 	asm("mov %0,sp" : "=&r" (sp) );
 	ao_cur_task->sp = (sp);
-	if ((uint8_t *) sp < &ao_cur_task->stack[0])
-		ao_panic (AO_PANIC_STACK);
 }
 
 static inline void ao_arch_restore_stack(void) {
-	uint32_t	sp;
-	sp = (uint32_t) ao_cur_task->sp;
-
 	/* Switch stacks */
-	asm("mov sp, %0" : : "r" (sp) );
+	asm("mov sp, %0" : : "r" (ao_cur_task->sp) );
 
 	/* Restore PRIMASK */
 	asm("pop {r0}");