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Subject:	Re: linker (binutils ld) is unable to resolve weak symbol, depends on object file order
To:	The Cygwin Mailing List <cygwin AT cygwin DOT com>
References:	<c302ea94-ae7b-f7b1-9d8f-0c2e31dc6bc7 AT ssi-schaefer DOT com> <ab8db982-e923-0ef0-e830-6fd2dca1aed2 AT gmail DOT com>
From:	Jon Turney <jon DOT turney AT dronecode DOT org DOT uk>
Message-ID:	<1b4f079b-55d9-e5d0-7b4a-5134fa7710b7@dronecode.org.uk>
Date:	Fri, 7 Jun 2019 12:58:35 +0100
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In-Reply-To:	<ab8db982-e923-0ef0-e830-6fd2dca1aed2@gmail.com>

On 07/06/2019 12:22, JonY wrote:
> On 6/7/19 10:04 AM, Michael Haubenwallner wrote:
>> Hi,
>>
>> so I'm encountering a strange problem related to object file order passed to
>> the linker, with any binutils and gcc version available to setup-x86_64.exe:
>>
>> $ cat weak-func.c
>> extern void weakfunc() __attribute__((weak));
>> void weakfunc() {}
>>
>> $ cat weak-main.c
>> extern void weakfunc() __attribute__((weak));
>> int main() { weakfunc(); }
>>
>> $ gcc -o weak.exe weak-func.c weak-main.c
>> SUCCESS
>>
>> But then, changing the order of input files on the command line does break
>> (does work on Linux of course):
>>
>> $ gcc -o weak.exe weak-main.c weak-func.c
>> /usr/lib/gcc/x86_64-pc-cygwin/8.3.0/../../../../x86_64-pc-cygwin/bin/ld: /tmp/ccIthYHe.o:weak-main.c:(.text+0xe): relocation truncated to fit: R_X86_64_PC32 against undefined symbol `weakfunc'
>> collect2: error: ld returned 1 exit status
>>
>> So the difference is that the object providing weakfunc is passed to
>> the linker after the object requiring weakfunc.
>>
>> Attached is the weak-func.sh script that does perform these commands.
>>
>> Thanks!
>> /haubi/
>>
> 
> Unfortunately, PE doesn't really have a concept of weak symbols like
> ELF, and is known to be broken in binutils.

see also: https://cygwin.com/faq.html#faq.programming.linker and the 
mail linked therein.



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