>>>>> "Dave" == Dave Korn <[EMAIL PROTECTED]> writes:
Dave> ----Original Message---- >> From: Shaun Jackman Sent: 02 August 2005 20:26 >> On 8/2/05, Paul Koning <[EMAIL PROTECTED]> wrote: >>> One of the things that continues to baffle me (and my colleagues) >>> is the bizarre way in which attributes such as "packed" work when >>> applied to structs. >>> >>> It would be natural to assume, as Shaun did, that marking a >>> struct "packed" (or, for that matter, "packed,aligned(2)") would >>> apply that attribute to the fields of the struct. >> This is exactly the behaviour suggested by the info docs: >> >> $ info gcc 'C Ext' 'Type Attr' ... Specifying this attribute for >> `struct' and `union' types is equivalent to specifying the >> `packed' attribute on each of the structure or union members. >> Dave> There are two separate issues here: Dave> 1) Is the base of the struct aligned to the natural alignment, Dave> or can the struct be based at any address Dave> 2) Is there padding between the struct members to maintain Dave> their natural alignments (on the assumption that the struct's Dave> base address is aligned.) Sure. But in Shaun's case it looks like (2) has been applied, except that the compiler doesn't adjust the generated code correctly. I would argue that "packed" applied to a whole struct should produce BOTH effects 1 and 2. There's a third case for which there appears to be no notation: 3) A pointer to a T that doesn't have the normal alignment of the type T. For example, as far as I can tell, GCC offers no way to say "pointer to unaligned int" -- short of creating a one-member struct. paul
