* David Miller <davem@xxxxxxxxxxxxx> [070602 22:09]: > Types must be aligned on their natural size, and GCC can assume > this everywhere you reference such types unless you use the > "packed" GCC attribute. And even with packed, the struct itself must be naturally aligned (unless itself is in a packed struct, if course). Funny example (I think from some dhcp-client): Make a packed struct with an 32 bit value on a 4*n+2 address, and (illegally[1] since it's the wrong alignment) cast a char pointer to an 4*m+2 address. Then the 32 bit value will be at an double even address. But as gcc may optimize for a 4*m address of the struct, it will even optimize a memcpy for that field away, replacing it with loads of the (only presumed) double-even addresses before and after and code to combine them. Thus you get a bus error for accessing a 32 bit value at an double-even address, because the struct it was in was not. Hochachtungsvoll, Bernhard R. Link [1] for proper values of "illegal". I guess that will only be something triggering undefined behaviour, not any other meaning of illegal. - To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
