[U-Boot-Users] Why are some global vars part of the image, and some not?

Jerry Van Baren gerald.vanbaren at smiths-aerospace.com
Mon Nov 6 19:03:02 CET 2006

Scott Wood wrote:
> Wolfgang Denk wrote:
>> In message <454BEF23.1020909 at freescale.com> you wrote:
>>> What about modifying the linker script so that all of bss is merged into 
>>> the image, i.e. treat it like 'data'?
>> That would mean that you have to allocate flash memory for  all  this
>> stuff,  which is typically in the 100...150 kB range, i. e. you would
>> double the memory footprint of U-Boot in flash memory.,
> That seems rather ridiculously large... perhaps some of the larger 
> chunks of that could be dynamically allocated, rather than leaving a 
> giant welcome mat for bugs by executing C code before the BSS is cleared 
> (especially if, as it appears to be in this case, the compiler and/or 
> linker is putting things in the BSS even when explicitly initialized to 
> zero, rather than just left uninitialized)?
> BTW, I'm only seeing about 19kB of BSS on an 8349EMDS build from the 
> current git head.
>> No, this is NOT acceptable. Don't even think of it.
> I don't think refusing to think about alternatives is conducive to good 
> software engineering.
> -Scott

You don't understand, u-boot _is_ what zeros bss so, until u-boot is 
running enough to zero bss, bss will be random garbage.  The stuff you 
are doing is very early initialization - using I2C to read SPD, which is 
before you even _have_ a normal bss because you don't even have your 
SDRAM active at this point.

Welcome to the Wacky World of Embedded where you must do everything 
yourself, and the world is populated with very sharp objects waiting to 
nail you if you do anything wrong.


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