Re: build musl for armv7m

[Szabolcs Nagy <nsz@port70.net>]

* weimingz@codeaurora.org <weimingz@codeaurora.org> [2016-06-22 23:04:18 -0700]:
> If it is not a weak symbol, you may get "multi-def" error. It depends on the
> obj/lib order on command line.

the only external symbol definition with non-weak binding
in the exit.o object is exit.

so the only way exit.o can get linked is an undefined reference
to exit.

you only need to make sure that -lc is at the end of the cmdline
when you want to interpose exit with your own definition
(then libc exit.o wont get linked in).

but to repeat rich: interposing libc symbols can break things.

> If it is a weak symbol, then a non-weak symbol can override it.
> 
> Anyway, your comment reminds me that we can use -wrap=exit to override it.
> So no change is needed.
> 
> btw, will you commit the change of those .s files for armv7m ?
> 
> Thanks,
> Weiming
> 
> On 2016-06-22 21:22, Rich Felker wrote:
> >On Wed, Jun 22, 2016 at 05:21:54PM -0700, Zhao, Weiming wrote:
> >>Fixed.
> >>
> >>Btw, can we make exit() weak function? (patch attached)
> >>
> >>This allows user code to redefine it because in baremetal
> >>environment, sometime we want to customize it. For example, some
> >>code never exits, so we can define a dummy exit() and thus save code
> >>size.
> >
> >No, this is a hack and is not even needed to do what you're asking
> >for. The way linking an archive works, an object in the archive is
> >only pulled in to the link process when it satisfies an undefined
> >symbol reference, and if you defined your own exit, then exit.o would
> >never have reason to get linked.
> >
> >But there are all sorts of things that can break unexpectedly from
> >redefining standard functions, which is why it's UB and this is not
> >supported usage.
> >
> >Rich