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Looking for a way to not place any static data in BSS section

Adam Openshaw
Note: This was originally posted on 2nd October 2012 at http://forums.arm.com

The ARM compiler is very strict (and formidable) at placing zero initialized or uninitialized static data > 8 bytes into the BSS section to save space in the image.  I have a use case where I do not want ANY static data in BSS.  I want all of it to go into RO/RW-DATA sections only. 

I've scoured the web looking for something similar or equivalent to the GNU C compiler's -fno-zero-initialized-in-bss option for RVCT, but cannot find anything.  I'm compiling with DS-5. 

Does anyone know if there is a way to compile without placing any static data into the BSS section?  Placing static data into a BSS section is an optimization, and it's only natural that you should be able to disable it.

Thanks,
Meiyo
  • Note: This was originally posted on 2nd October 2012 at http://forums.arm.com

    Hi, I don't know how to do it in DS-5, but in Keil, you have something called the scatter file where you can use linker commands to specifically place data in your desired memory regions. There's is no special (button-like) options to disable .bss sections.  Check if there's something similar in DS-5 but I think it should be because ARM is the developer of both.

    Good luck
  • Note: This was originally posted on 3rd October 2012 at http://forums.arm.com

    Hi Sasa,

    Thanks for your response.  I am aware that you are able to use the scatter loading procedure to place various sections like ZI and RW data in the same loadable region, but this is not quite what I am looking for.

    My problem exists because the .bss sections have a filesize of 0 bytes.  For my use case I need the static data to actually occupy space in the executable.  The only  way to do this seems to be to have the static data in the data section and not bss.

    I'm looking for any way to get around this optimization.  Being able to disable it is ideal, since it's nothing more than space optimization, but it's seeming less and less likely that this is supported for some reason. 

    Thanks again,
    Meiyo
  • Note: This was originally posted on 3rd October 2012 at http://forums.arm.com

    I was able to accomplish what I desired after consulting ARM support.  For anyone who is interested, here is the solution:

    The answer is using the --bss_threshold option when compiling.  The documentation on this option makes it seem like the only two options are: --bss_threshold=0 or --bss_threshold=8...

    [font=Verdana, Tahoma, Arial, Helvetica, sans-serif][size=2]
    Syntax
    [/size][/font][font=Verdana, Tahoma, Arial, Helvetica, sans-serif][size=2]--bss_threshold=numWhere:

    numis either:

    0place small global ZI data items in ZI data sections

    8place small global ZI data items in RW data sections.

    [/size][/font]



    It turns out, however, that the compiler is actually capable of accepting anything up to the maximum int, and anything below that size in bytes will be put into RW data instead of BSS.

    Regards,
    Meiyo