[avr-libc-dev] [bug #36124] Improve documentation on .bss clear when used in assembler

[Jan Waclawek]

URL:
  <http://savannah.nongnu.org/bugs/?36124>

                 Summary: Improve documentation on .bss clear when used in
assembler
                 Project: AVR C Runtime Library
            Submitted by: wek
            Submitted on: Sat 07 Apr 2012 02:02:23 PM GMT
                Category: Documentation
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Documentation
                  Status: None
        Percent Complete: 0%
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
                 Release: Any
           Fixed Release: None

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Details:

Newer builds of the avr-gcc toolchain, such as WinAVR20100110, or builds
including the PR18145 fixup (4.7+), contain a patch which results in
conditional linking of the .bss cleanup loop only if it is needed for the C
source (similarly for the initialized .data). This may lead to surprising
behaviour when such variables are defined only in assembler parts of a
project.

It is therefore suggested to add something like the following text to
http://www.nongnu.org/avr-libc/user-manual/assembler.html after "For devices
that have RAM, initializing the RAM variables can also be utilized.", or
http://www.nongnu.org/avr-libc/user-manual/mem_sections.html#sec_dot_init into
the chapters dealing with .data and .bss sections, or both as appropriate:

Note: To ensure that variables in .bss section are zeroed upon startup, add
the following line to the assembler source:
.global __do_clear_bss

To ensure that variables in .data section are initialized from FLASH during
startup, add the following line to the assembler source:
.global __do_copy_data

(This submission is result of discussion on AVRFreaks
http://www.avrfreaks.net/index.php?name=PNphpBB2&file=viewtopic&t=119131&highlight=
)




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