I solved the problem using something like this
extern const struct s s;
extern struct s s_mutable;
Define s and s_mutable via a basic asm statement in the .data section.
For example:
https://git.rtems.org/rtems/tree/cpukit/score/cpu/sparc/rtems/score/cpu.h#n1327
https://git.rtems.org/rtems/tree/cpukit/score/cpu/sparc/rtems/score/sparcimpl.h#n71
On 22/06/16 09:00, Sebastian Huber wrote:
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@xxxxxxxxxxxxxxxxxx
PGP : Public key available on request.
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