linker (binutils ld) is unable to resolve weak symbol, depends on object file order

linker (binutils ld) is unable to resolve weak symbol, depends on object file order

[Michael Haubenwallner]

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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/

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Re: linker (binutils ld) is unable to resolve weak symbol, depends on object file order

[JonY]

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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.


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Re: linker (binutils ld) is unable to resolve weak symbol, depends on object file order

[Jon Turney]

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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