Messages in this thread | | | Date | Sun, 31 Aug 2003 03:27:59 +0200 | From | "J.A. Magallon" <> | Subject | Re: [2.4] gcc3 warns about type-punned pointers ? |
| |
On 08.29, J.A. Magallon wrote: > Hi all... > > gcc3 gives this warning when using the __set_64bit_var function: > > /usr/src/linux/include/asm/system.h:190: warning: dereferencing type-punned pointer will break strict-aliasing rules > > Is it a potential problem ? > > This seems to cure it: > > --- linux-2.4.22-jam1m/include/asm-i386/system.h.orig 2003-08-29 00:26:41.000000000 +0200 > +++ linux-2.4.22-jam1m/include/asm-i386/system.h 2003-08-29 00:26:55.000000000 +0200 > @@ -181,8 +181,8 @@ > { > __set_64bit(ptr,(unsigned int)(value), (unsigned int)((value)>>32ULL)); > } > -#define ll_low(x) *(((unsigned int*)&(x))+0) > -#define ll_high(x) *(((unsigned int*)&(x))+1) > +#define ll_low(x) *(((unsigned int*)(void*)&(x))+0) > +#define ll_high(x) *(((unsigned int*)(void*)&(x))+1) >
How about something like this:
typedef unsigned long long u64; typedef unsigned long u32; typedef unsigned short u16; typedef unsigned char u8;
union u64_split { u64 ll; u32 l[2]; u16 w[4]; u8 b[8]; };
void f() { u64 a;
int l = ((union u64_split)a).l[0]; int h = ((union u64_split)a).l[1]; }
The clean way todo it without pointer arithmetic...
And with a modern gcc (anonymous structs):
union u64_split { u64 x; struct { u32 l32,h32; }; struct { u16 ll16,lh16,hl16,hh16; }; };
So you just write:
int l = ((union u64_split)a).l32; u16 word = ((union u64_split)a).ll16;
I think it is better with structs, to take care of endianness if needed.
-- J.A. Magallon <jamagallon@able.es> \ Software is like sex: werewolf.able.es \ It's better when it's free Mandrake Linux release 9.2 (Cooker) for i586 Linux 2.4.22-jam1m (gcc 3.3.1 (Mandrake Linux 9.2 3.3.1-1mdk)) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |