diff options
| author | Keith Packard <keithp@keithp.com> | 2016-12-17 20:58:36 -0800 |
|---|---|---|
| committer | Keith Packard <keithp@keithp.com> | 2016-12-17 21:04:33 -0800 |
| commit | 89ecc32b90565ace078c4a84d4406a4d1f86821a (patch) | |
| tree | 3b32f1d922380b3dfd25db75552a30dc84c24d41 /src/stm/stm32l.h | |
| parent | f650211f9e99e1d3d0ae13ae559dd1c082f71545 (diff) | |
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>
Diffstat (limited to 'src/stm/stm32l.h')
| -rw-r--r-- | src/stm/stm32l.h | 2 |
1 files changed, 1 insertions, 1 deletions
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; |