On 13/02/12 02:13, Ian Lance Taylor wrote:
> The linker tends to only complain if an undefined symbol is used. I
> don't know if that explains what you are seeing, but perhaps it does.
>
> Ian
It does. The appearance of working on gcc3 was indeed misleading.
Adding an assignment to Localfoo it relents to produces
[Linker error] undefined reference to `Foo.Foodata'
I was finally able to perform the aliasing doing it directly in assembler.
For reference , this is what worked for me
#define ALIAS_MEMBER(name, instance,member) \
static void instance ## __ ## alias__ ## member ## __ ## function
(void) __attribute__((used)); \
static void instance ## __ ## alias__ ## member ## __ ## function
(void) { \
const size_t member_offset = offsetof(typeof(instance), member); \
asm(".global " # member "\n" "\t.set " #name "," #instance " + %0\n" : \
/* No output */ : /* input */ "g" ( member_offset ) ); } \
extern typeof(instance.member) name;
Some notes:
- You need to enable optimizations, so the constant is converted into a
literal (doesn't work in -O0)
- The instance shall have an initialiser (even if you don't care about
the value), so that
the variable it's placed in .bss, and not as a .comm (it may produce a
'can't be equated to
common symbol' error or silently skip your symbol)
- It doesn't seem to work for all targets. YMMV.
