From: Segher Boessenkool > Sent: 06 October 2021 22:27 > > On Thu, Oct 07, 2021 at 05:44:00AM +0900, Stafford Horne wrote: > > You have defined of_get_cpu_hwid to return u64, will this create compiler > > warnings when since we are storing a u64 into a u32? > > > > It seems only if we make with W=3. > > Yes. This is done by -Wconversion, "Warn for implicit conversions that > may alter a value." > > > I thought we usually warned on this. The microsoft compiler does - best to turn all those warnings off. > This warning is not in -Wall or -Wextra either, it suffers too much from > false positives. It is very natural to just ignore the high bits of > modulo types (which is what "unsigned" types *are*). Or the bits that > "fall off" on a conversion. The C standard makes this required > behaviour, it is useful, and it is the only convenient way of getting > this! I've also seen a compiler convert: struct->char_member = (char)(int_val & 0xff); into: reg = int_val; reg &= 0xff; // for the & 0xff reg &= 0xff; // for the cast struct->char_member = low_8bits(reg); You really don't want the extra noise. I'll bet that (char)int_val is actually an arithmetic expression. So its type will be 'int'. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
