On Tue, Mar 28, 2006 at 12:19:41AM +0200, Joerg Schilling wrote: >Steve McIntyre <[EMAIL PROTECTED]> wrote: >> >> As the link that I posted up-thread said, #pragma pack(1) does not >> force alignment within a structure on arm, as that would clash with >> the arm ABI. If you _must_ do things that way, you have to use >> __attribute__((packed)). Better/more portable would be to have a >> simple byte array rather than a packed structure. > >I would call this default behavior of GCC a bug. > >I'll try to verify this with the C99 standard, but in case GCC is able >to create working code at all (using __attribute__((packed))), it seems like >the default behavior does not make sense. > >Note that countless C-programs depend on sizeof(struct something) returning >useful values.
In what way are these not useful values? They may not be what you expect, but It's a long-known feature of C that making assumptions about structure layout and alignment _will_ bite you. The default behaviour here is (apparently) as specified by the designers of the hardware in this case. Alignment _really_ matters for performance on some architectures, and this is one of them. The quick-hack fix is to use the __attribute__((packed)) patch; the real fix is to stop depending on structure setup like this - use a byte array and work within that as appropriate. -- Steve McIntyre, Cambridge, UK. [EMAIL PROTECTED] Who needs computer imagery when you've got Brian Blessed? -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
