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Re: [avr-libc-dev] [RFC] sections stub patch

From: Theodore A. Roth
Subject: Re: [avr-libc-dev] [RFC] sections stub patch
Date: Wed, 28 Aug 2002 09:41:24 -0700 (PDT)

On Wed, 28 Aug 2002, Joerg Wunsch wrote:

:) > +  <tr>
:) > +  <td><tt>.init4</tt></td>
:) > +  <td>Copies data from flash to SRAM. [Is this BSS init?]</td>
:) > +  </tr>
:) It is both, initializing .data and initializing .bss.  In Unix-like
:) targets, .data is normally initialized by the OS directly from the
:) executable file.  Since this is impossible in an MCU environment,
:) avr-gcc instead takes care of appending the .data variables after
:) ..text in the flash ROM image.  .init4 then defines the function
:) weakly() which takes care of copying the contents of .data from the
:) flash to SRAM.

That's what I thought was happening. You mind if I just move the above
into the dox?

:) Initializing .bss just means to zero it out, but that's indeed also
:) done inside .init4.
:) Btw., if you look into the ld script(s), you'll notice that there's
:) also .init6 and .fini6 used for C++ constructors/destructors, .fini9
:) is used to implement _exit() (normally obviously just empty), and
:) ..fini0 is used for the infinite loop.  All of this seems to be
:) implicit knowledge of avr-gcc.

Missed those. Thanks. Is there also ".fini[0-9]"? Are they always executed
in order from 0 to 9? Ah, to answer my own question, looking at one of my
map files:

 .fini0         0x00000db2        0x2
                0x00000db4                _etext = .

so .initN is 0 -> 9 and .finiN is 9 -> 0.

How does the .ctors and .dtors section work with .init6/.fini6 then?

One more question: Is it possible to have multiple functions assigned into
the same .initN section? I see this in a map file:

 .init4         0x00000098       0x1a
                0x00000098                __do_copy_data
 .init4         0x000000b2       0x10
                0x000000b2                __do_clear_bss

Which seems to imply you can.

:) Hmm, if you put that here, the FAQ could be updated to just xref this
:) part instead of using the examples directly there.

That was the plan, eventually. ;-)

I also want to move the faq in the inline asm doc into the main faq.

Ted Roth

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