From fe25510fc23031f1a3c1b42edd37067d1989a9f6 Mon Sep 17 00:00:00 2001 From: Keith Packard Date: Sat, 17 Dec 2016 20:58:36 -0800 Subject: 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 --- src/stm/stm32l.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'src/stm/stm32l.h') diff --git a/src/stm/stm32l.h b/src/stm/stm32l.h index 463125e2..be1e1d65 100644 --- a/src/stm/stm32l.h +++ b/src/stm/stm32l.h @@ -1961,7 +1961,7 @@ union stm_usb_bdt { #define STM_USB_BDT_SIZE 8 -extern uint8_t stm_usb_sram[]; +extern uint8_t stm_usb_sram[] __attribute__ ((aligned(4))); struct stm_exti { vuint32_t imr; -- cgit v1.2.3