2010/5/19 Andrew Haley <aph@xxxxxxxxxx>: > On 05/19/2010 03:29 AM, YC Wang wrote: > >> When gcc processes a strucure declaration, what rules it will use? As >> far as I know, gcc is supposed to conform to the platform ABI. For >> example, below is extracted from the SysV i386 ABI: >> >> - An entire structure or union object is aligned on the same boundary as >> its most strictly aligned member. >> >> - Each member is assigned to the lowest available offset with the >> appropriate alignment. This may require internal padding, depending on the >> previous member. >> >> - A structure's size is increased, if necessary, to make it a multiple >> of the alignment. This may require tail padding, depending on the last >> member. >> >> So, should gcc (whatever versions) always comform to these rules >> (assume we don't specify special attributes or options)? > > Yes. > >> I ask this question because I just read the paper >> "stable_api_nonsense" by Greg KH from Linux kernel Documentation, >> and begin with line 54 the paper says "Depending on the version of >> the C compiler you use, different kernel data structures will >> contain different alignment of structures". > > We try to follow the ABI but sometimes we make mistakes. However, > it's impossible to tell what he's talking about for sure. You'd have > to ask him. > > Andrew. > Actually, I had mailed him, but his mail-bot suggested me to ask mailing lists. Maybe only himself can answer me this time. Anyway, thank you for the reply. YC wang
