Re: [arm-gnu] Getting linker data into a C structure

[42Bastian <list-bastian.schick@xxxxxxxxxxx>]

Am 10.05.2010 15:55, schrieb Andrew Kohlsmith (mailing lists account):


> extern const uint32_t _etext, _data_len;
> 
> But the compiler complains bitterly about this ("error: initializer element is 
> not constant").  The solution that I have found in a couple of places online 
> is this:
> 
> extern const uint32_t _etext[], _data_len[];

A symbol defined in the linker script is an address.

const uint32_t _etext;

defines a variable/value. Remember, you need &_etext to get the address of
that variable.


> and then to cast them back to uint32_t in the structure initializer:
> 
> const fw_struct_t fw_struct = {
> 	.checksum = 0,		/* filled in by checksummer */
> 	.version = VERSION_CODE,
> 	.initdata_loc = (uint32_t)_etext,

Shouldn't this be a (char *) ?

> 	.initdata_len = (uint32_t)_data_len,
> };

> 
> This looks wrong, it feels wrong, but it works beautifully. ld correctly 
> supplies the values for the extern consts and life is good.
> 
> Can anyone explain to me like I'm a six year old why on earth I need to 
> specify the external constant integers as integer arrays? Why does GCC 

Only if defined in the linker !


-- 
42Bastian
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