COMMON symbols...

[Nick Clifton]

Hi Dave,

>   So I think that ld isn't zero-filling the space it allocates to the common
> symbols, but just letting them take whatever values happen to be in the host
> memory space that has been allocated by the linker to build up the output
> section.
> 
>   Is there any way to work around this?  I couldn't get useful results with
> the FILL expressions, which I suppose makes sense because the space is used.
> And I couldn't get the FORCE_COMMON_ALLOCATION directive or -d switch to
> help me out either.
> 
>   Does anyone know of a way to get the result I want from the linker?

I strongly suspect that this is a linker "feature" in that it has never 
had to zero-fill the file space that is going to be used for common 
symbols because it assumes that they are always going to be going into a 
  section with the SHT_NOBITS flag set.  ie this is a bug and the linker 
ought to check for this and zero the memory it writes out if necessary.

Anyway the only way that I can think of to fix this in a linker script 
is to use overlays.  This *might* work, but I have not tried it.

>   (And before you ask, I can't just give gcc -fno-common, even though that
> would move the common symbols into bss for me and hence get them
> zero-filled, because the option's  a bit b0rked somewhere in my toolchain

Incidentally if you fix -fno-common you could then add the 
-ffno-zero-initialized-in-bss switch and then not have to modify your 
linker script at all....

Cheers
   Nick