gps_time_t struct can cause alignment problems on ARMv6/ARMv7

[njoubert]

In gpstime.h

typedef struct attribute((packed)) {
double tow; /< Seconds since the GPS start of week. */
u16 wn; /< GPS week number. */
} gps_time_t;

ARMv6 and ARMv7 architectures support unaligned loads for everything everything except double-word structures.

This struct, since it is packed, can cause alignment crashes if an array of these are created and loaded, or if it is inserted into another packed struct.

[njoubert]

OK, so this appears to be caught by the compiler, that generates two LDR instructions that can be word-unaligned, rather than a LDRD instruction which has to be word-aligned.

To cause a segfault because of an unaligned LDRD, you can use this snippet:

u8 blah[9] = {1,1,1,1,1,1,1,1,1};
printf("blah = %lf", ((double)&blah[1]));