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Subject: Re: linker (binutils ld) is unable to resolve weak symbol, depends on object file order
To: cygwin AT cygwin DOT com
References: <c302ea94-ae7b-f7b1-9d8f-0c2e31dc6bc7 AT ssi-schaefer DOT com>
From: JonY <10walls AT gmail DOT com>
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Date: Fri, 7 Jun 2019 11:22:45 +0000
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From: JonY <10walls AT gmail DOT com>
To: cygwin AT cygwin DOT com
Message-ID: <ab8db982-e923-0ef0-e830-6fd2dca1aed2 AT gmail DOT com>
Subject: Re: linker (binutils ld) is unable to resolve weak symbol, depends on
 object file order
References: <c302ea94-ae7b-f7b1-9d8f-0c2e31dc6bc7 AT ssi-schaefer DOT com>
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On 6/7/19 10:04 AM, Michael Haubenwallner wrote:
> Hi,
>=20
> 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.e=
xe:
>=20
> $ cat weak-func.c
> extern void weakfunc() __attribute__((weak));
> void weakfunc() {}
>=20
> $ cat weak-main.c
> extern void weakfunc() __attribute__((weak));
> int main() { weakfunc(); }
>=20
> $ gcc -o weak.exe weak-func.c weak-main.c
> SUCCESS
>=20
> But then, changing the order of input files on the command line does break
> (does work on Linux of course):
>=20
> $ 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
>=20
> So the difference is that the object providing weakfunc is passed to
> the linker after the object requiring weakfunc.
>=20
> Attached is the weak-func.sh script that does perform these commands.
>=20
> Thanks!
> /haubi/
>=20

Unfortunately, PE doesn't really have a concept of weak symbols like
ELF, and is known to be broken in binutils.


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