How do I tell GCC that a global variable is immutable after initialization?

[Sebastian Huber <sebastian dot huber at embedded-brains dot de>]

Hello,

is there a way to tell GCC that a global variable is immutable after 
initialization? For example

struct {
    int (*f)(void);
} s;

int f(void)
{
    int a;
    int b;

    a = (*s.f)();
    b = (*s.f)();

    return a + b;
}

yields on ARMv8 for example

f:
        push    {r4, r5, r6, lr}
        movw    r4, #:lower16:s
        movt    r4, #:upper16:s
        ldr     r3, [r4]
        blx     r3
        ldr     r3, [r4] <- I would like to get rid of this load here
        mov     r5, r0
        blx     r3
        add     r0, r5, r0
        pop     {r4, r5, r6, pc}

The

a = (*s.f)();

is a call to a global function, so GCC must assume that s might have 
changed afterwards. I would like to get rid of the second load of s.f. 
Is there a special attribute to tell GCC that s is essentially 
immutable? I cannot use the const qualifier, since the structure is 
initialized during system start.

--
Sebastian Huber, embedded brains GmbH

Address : Dornierstr. 4, D-82178 Puchheim, Germany
Phone   : +49 89 189 47 41-16
Fax     : +49 89 189 47 41-09
E-Mail  : sebastian.huber@embedded-brains.de
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