[U-Boot] [PATCH v2 1/2] arm920t/at91/reset.c: fix weak reset_board()

Andreas Bießmann
2010-11-04T10:54:32Z

Dear Sebastien Carlier,

Am 04.11.2010 04:27, schrieb Sebastien Carlier:
> These weakly defined empty functions prevent the strong definition
> from being linked in.
>
> For example, libarm.a contains a weak symbol 'red_LED_on', which is
> expected to be defined (strongly) in the board library. Because
> archive libraries are being used, this fails (testing with binutils
> 2.20.1), and only the empty __red_LED_on stub is linked in; the
> red_LED_on definition in the board library is throw away.

I have detected this issue yesterday evening too.

> This behavior is documented and it is the intended one; from
> http://www.sco.com/developers/gabi/latest/ch4.symtab.html:
>
>> When the link editor searches archive libraries [see ``Archive
>> File'' in Chapter 7], it extracts archive members that contain
>> definitions of undefined global symbols.
>> The member's definition may be either a global or a weak symbol.
>> The link editor does not extract archive members to resolve
>> undefined weak symbols. Unresolved weak symbols have a zero value.
>
> Empty weak definitions would have to be supplied to the linker only
> _after_ the strong definitions have been provided.

So it would be a work around to change Makefile from:

---8<---
__LIBS := $(subst $(obj),,$(LIBS)) $(subst $(obj),,$(LIBBOARD))
--->8---

to:

--->8---
__LIBS := $(subst $(obj),,$(LIBBOARD)) $(subst $(obj),,$(LIBS))
---8<---

This could work cause in most cases the strong definitions are in
$(LIBBOARD) and overload the weak functions in $(LIBS).

But this is just a work around and will not fit any use-case of weak
functions. The root cause seems to be a linker problem. But I dunno
whether it is a mis-usage or a bug. Any gcc-guys here to comment?

> Leaving undefined weak symbols and testing for NULL-ity at call sites
> seems to be a more robust approach.
>
> Note that with some ld versions (at least with 2.20.1), ld creates PLT
> entries for undefined weak symbols and crashes when the PLT-related
> sections (.plt, .got.plt, and .rel.plt) are discarded...

This seems to be the main issue here ... but how to get it solved?

regards

Andreas Bie?mann