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Re: [lwip-users] Initialization of global variables

From: Simon Goldschmidt
Subject: Re: [lwip-users] Initialization of global variables
Date: Fri, 5 Nov 2010 19:53:25 +0100

Hey Piotr,

I hate to turn you down on that, but the variables are deliberately not being 
initialized: when not initialized (and thus implicitly zeroed at startup), they 
are put into the uninitialized section and no space on disk/in flash is needed. 
However when they are initialized to NULL, they are put NGO the initialized 
data section, which is present on disk/in flash, too.

As to the portability: the C standard requires non initialized data to be 
initialized to zero at startup. It is a common error in self-made ports to 
leave out the zeroing of the uninitialized data section (.bss for gnu bcc).


 Piotr Piwko <address@hidden> wrote:

> Hello,
> I currently implement the LwIP stack under u-boot environment and I
> have one notice regarding global variables initialization. I think
> that every global variable which are not static should be initialized
> by NULL or 0 value. I mean for example:
> file tcp.c:
> struct tcp_pcb *tcp_bound_pcbs;
> union tcp_listen_pcbs_t tcp_listen_pcbs;
> struct tcp_pcb *tcp_active_pcbs;
> struct tcp_pcb *tcp_tw_pcbs;
> file udp.c:
> struct udp_pcb *udp_pcbs;
> file netif.c:
> struct netif *netif_list;
> struct netif *netif_default;
> If I leave they uninitialized, after compilation and link operation
> they will contain random values which causes the system crash during
> LwIP initialized functions. Assumption that they will be automatically
> filled by 0 is wrong and non-portable.
> This modification can really save a lot of time during integration :)
> Anyway I am impressed with LwIP project. It is very useful part of
> software. Good job guys!
> Regards,
> -- 
> Piotr Piwko
> http://www.embedded-engineering.pl/
> _______________________________________________
> lwip-users mailing list
> address@hidden
> http://lists.nongnu.org/mailman/listinfo/lwip-users

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