On Thu, 17 Aug 2023, Tony Josi via Gcc-help wrote: > I would also like to understand the reasoning behind this warning. When a > struct is packed explicitly it's expected that the padding required for the > alignment of the fields will be removed and it might cause inefficient data > access. > It makes sense to warn when a packed attribute has no effect on struct > layout but I fail to understand why specific fields that are already > aligned in a struct are warned when the whole struct is packed. No, 'ch1' in your example does not keep the original 32b alignment: the attribute reduces the size of the struct from 12 to 10 bytes, so it can no longer be 4-byte aligned. Worse, the attribute is documented to reduce struct alignment down to one byte, and 'ch1' has the same alignment as the whole struct. Alexander
