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Message-ID: <6565c836f72584243dd443e4cd291763@codeaurora.org>
Date: Thu, 23 Jun 2016 07:22:57 -0700
From: weimingz@...eaurora.org
To: weimingz@...eaurora.org
Cc: musl@...ts.openwall.com, Rich Felker <dalias@...ifal.cx>, Rich Felker
<dalias@...c.org>
Subject: Re: build musl for armv7m
Correct. Thank you Szabolcs.
Weiming
On 2016-06-23 02:57, Szabolcs Nagy wrote:
> * weimingz@...eaurora.org <weimingz@...eaurora.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
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