Hi

> Typically this means you are calling a function that is not correctly
> marked as Thumb code, so the linker is helpfully switching you back to
> ARM mode; check the target symbol.
> 
That was also my first thought, but it happens also with calls in the same file.
So the code:

------------------------------------------------------------

typedef void(*fpt)(int);

void func(int a){
	a = a*a;
}

int main(void){
	fpt p;
	p = func;
	p(3);
	for(;;)
		;
	return 0;
}

------------------------------------------------------------

compiles to:

------------------------------------------------------------

000001b0 <func>:
 1b0:   b480            push    {r7}
 1b2:   b083            sub     sp, #12
 1b4:   af00            add     r7, sp, #0
 1b6:   6078            str     r0, [r7, #4]
 1b8:   687b            ldr     r3, [r7, #4]
 1ba:   687a            ldr     r2, [r7, #4]
 1bc:   fb02 f303       mul.w   r3, r2, r3
 1c0:   607b            str     r3, [r7, #4]
 1c2:   f107 070c       add.w   r7, r7, #12
 1c6:   46bd            mov     sp, r7
 1c8:   bc80            pop     {r7}
 1ca:   4770            bx      lr

000001cc <main>:
 1cc:   b580            push    {r7, lr}
 1ce:   b082            sub     sp, #8
 1d0:   af00            add     r7, sp, #0
 1d2:   f240 13b1       movw    r3, #433        ; 0x1b1
 1d6:   f2c0 0300       movt    r3, #0
 1da:   607b            str     r3, [r7, #4]
 1dc:   687b            ldr     r3, [r7, #4]
 1de:   f04f 0003       mov.w   r0, #3
 1e2:   4798            blx     r3
 1e4:   e7fe            b.n     1e4 <main+0x18>
 1e6:   bf00            nop

------------------------------------------------------------

I especially took a look at the implementation of the function pointer call.
But also the normal funtion returns with a bx.

Best regards,
  Daniel Otte