Default struct fields alignment

[CTabo.1]

Hello,

which is the default struct fields alignment policy of GCC, on STM32 MCU?

 

I have the following structure:

 

typedef struct

{

  uint32_t   param1;

  float      param2;

  uint16_t   param3;

} PARAM_T;

 

 

I expected a size of 10 bytes, but it is 12 instead, because a two bytes padding has been inserted between param2 and param3, to align this last one to a 4 bytes multiple address.

 

Why this padding has been added?
'param3' is a uint16_t field, so I expected a 2 bytes address alignment and not a 4 bytes one.

 

Thank you,

Carlo

 

[Tesla DeLorean]

Why, so the processor doesn't fault.

The CM0(+) being particularly fussy.

Other CMx will fault on misaligned LDRD/STRD.

For compact structures for files perhaps __packed or similar,  but then you must address misalignment issues yourself. 

Situations where you array the data, or make composite structures. 

 

[CTabo.1]

Thank you @Tesla DeLorean, for the very quick response.

So you are saying that all fields inside a struct, by default, are 4 bytes aligned, despite of their type.
Isn't it?

Thank you,
Carlo