Re: Padding in gcc

[Rodrigo Rubira Branco <rrbranco@br.ibm.com>]

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On Mon, 2007-07-09 at 17:10 +0530, Rajat Jain wrote:
> Hi,
> 
> Perhaps a little offtopic but no harm in trying ...
> 
> Can we always rely on the fact that gcc will pad the following structure?
> 
> typedef struct {
>     int descrp;      SYSCALL64_STRUCT_ATTR;
>     (Automatic padding here?)
>     long long pos;   SYSCALL64_STRUCT_ATTR;
>     int mode;        SYSCALL64_STRUCT_ATTR;
> } lseek64_t;
> 
> What is the correct way to make it portable? Explicitly added padding fields?
> 
> Thanks,
> 
> Rajat
> -
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Unless you explicitly say this structure is packed
(__attribute__((packed))) gcc will align it... for sure you need to take
care for yourself when you are trying to use different cache lines for
members of this structure.

Anyway, the code itself is portable, since you are just using C.


cya,


rodrigo (BSDaemon).

-- 
Rodrigo Rubira Branco
Software Engineer 
Advanced Linux Response Team (ALRT) / Linux on Power Toolchain
IBM Linux Technology Center (IBM/LTC)
rrbranco@br.ibm.com

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