llvm dev - Feb 2014 - [LLVMdev] Fwd: [windows) how to use weak references with llvm 3.4 and windows?

Hello,

I'm generating C code (and the resulting obj files) using llvm 3.4 for both
unix and windows.
And I use the dreaded weak references, that, for windows, are not too
widely supported.

When I link my application on linux, I have no issue.
But when I'm doing the same on windows using mingw I got a duplicate symbol
error :

..\robovm-0.0.8\lib\robovm-rt.jar\dalvik\system\BlockGuard$BlockGuardPolicyException.class.o:(.text$dalvik_system_BlockGuard$24BlockGuardPolicyException_getPolicy__I_lookup[_dalvik_system_BlockGuard$24BlockGuardPolicyException_getPolicy__I_lookup]+0x0):
multiple definition of
`dalvik_system_BlockGuard$24BlockGuardPolicyException_getPolicy__I_lookup'
..\Temp\robovm3774596063679264132.tmp\linker.o:(.text+0x340): first defined
here
..\robovm-0.0.8\lib\robovm-rt.jar\dalvik\system\BlockGuard$BlockGuardPolicyException.class.o:(.text$dalvik_system_BlockGuard$24BlockGuardPolicyException_getPolicyViolation__I_lookup[_dalvik_system_BlockGuard$24BlockGuardPolicyException_getPolicyViolation__I_lookup]+0x0):
multiple definition of
`dalvik_system_BlockGuard$24BlockGuardPolicyException_getPolicyViolation__I_lookup'
..\Temp\robovm3774596063679264132.tmp\linker.o:(.text+0x350): first defined
here
..\robovm-0.0.8\lib\robovm-rt.jar\dalvik\system\BlockGuard$BlockGuardPolicyException.class.o:(.text$dalvik_system_BlockGuard$24BlockGuardPolicyException_getMessage__Ljava_lang_String$3B_lookup[_dalvik_system_BlockGuard$24BlockGuardPolicyException_getMessage__Ljava_lang_String$3B_lookup]+0x0):
multiple definition of
`dalvik_system_BlockGuard$24BlockGuardPolicyException_getMessage__Ljava_lang_String$3B_lookup'

Because those symbols are declared as weak.

What is the status about the support of weak symbols on windows?
Are they supposed to work? Are they supposed to *never *work ?

Do you know any way to fix this (or work around it). I use weak symbols
everywhere in my code generation, so I would prefer a fix that doesn't
involve to rewrite my code.

I'm considering rewriting the obj files using objcopy.
Has this any chance to work ?
Here are the o.

Cheers,
Carl.
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20140210/ddacc877/attachment.html>

COFF doesn't support the same kind of concept of 'weak' that ELF
does.
 This is the issue that users brought up with mingw:
https://sourceware.org/bugzilla/show_bug.cgi?id=9687

Instead, COFF supports weak externals, which you can use like:

$ cat t.c
int foo() __attribute__((weak));
int main() {
  if (foo)
    return foo();
  return 13;
}

$ cat t2.c
int foo() {
  return 42;
}

$ clang t.c t2.c -o t && ./t ; echo $?
42

So, we got the definition of foo from t2.c.  If t2.c hadn't been linked,
foo would be null.


On Mon, Feb 10, 2014 at 6:28 AM, Carl <name.is.carl at gmail.com> wrote:
>
> Hello,
>
> I'm generating C code (and the resulting obj files) using llvm 3.4 for
> both unix and windows.
> And I use the dreaded weak references, that, for windows, are not too
> widely supported.
>
> When I link my application on linux, I have no issue.
> But when I'm doing the same on windows using mingw I got a duplicate
> symbol error :
>
>
..\robovm-0.0.8\lib\robovm-rt.jar\dalvik\system\BlockGuard$BlockGuardPolicyException.class.o:(.text$dalvik_system_BlockGuard$24BlockGuardPolicyException_getPolicy__I_lookup[_dalvik_system_BlockGuard$24BlockGuardPolicyException_getPolicy__I_lookup]+0x0):
> multiple definition of
>
`dalvik_system_BlockGuard$24BlockGuardPolicyException_getPolicy__I_lookup'
> ..\Temp\robovm3774596063679264132.tmp\linker.o:(.text+0x340): first
> defined here
>
..\robovm-0.0.8\lib\robovm-rt.jar\dalvik\system\BlockGuard$BlockGuardPolicyException.class.o:(.text$dalvik_system_BlockGuard$24BlockGuardPolicyException_getPolicyViolation__I_lookup[_dalvik_system_BlockGuard$24BlockGuardPolicyException_getPolicyViolation__I_lookup]+0x0):
> multiple definition of
>
`dalvik_system_BlockGuard$24BlockGuardPolicyException_getPolicyViolation__I_lookup'
> ..\Temp\robovm3774596063679264132.tmp\linker.o:(.text+0x350): first
> defined here
>
..\robovm-0.0.8\lib\robovm-rt.jar\dalvik\system\BlockGuard$BlockGuardPolicyException.class.o:(.text$dalvik_system_BlockGuard$24BlockGuardPolicyException_getMessage__Ljava_lang_String$3B_lookup[_dalvik_system_BlockGuard$24BlockGuardPolicyException_getMessage__Ljava_lang_String$3B_lookup]+0x0):
> multiple definition of
>
`dalvik_system_BlockGuard$24BlockGuardPolicyException_getMessage__Ljava_lang_String$3B_lookup'
>
> Because those symbols are declared as weak.
>
> What is the status about the support of weak symbols on windows?
> Are they supposed to work? Are they supposed to *never *work ?
>
> Do you know any way to fix this (or work around it). I use weak symbols
> everywhere in my code generation, so I would prefer a fix that doesn't
> involve to rewrite my code.
>
> I'm considering rewriting the obj files using objcopy.
> Has this any chance to work ?
> Here are the o.
>
> Cheers,
> Carl.
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20140210/fc028ac7/attachment.html>

Thanks for your clear answer. Do you know what modifier should I use to
declare such weak symbols in my llvm intermediate code?

So that it can be compiled to the .o file with the weak attribute ?
Le 10 févr. 2014 19:44, "Reid Kleckner" <rnk at google.com> a
écrit :
> COFF doesn't support the same kind of concept of 'weak' that
ELF does.
>  This is the issue that users brought up with mingw:
> https://sourceware.org/bugzilla/show_bug.cgi?id=9687
>
> Instead, COFF supports weak externals, which you can use like:
>
> $ cat t.c
> int foo() __attribute__((weak));
> int main() {
>   if (foo)
>     return foo();
>   return 13;
> }
>
> $ cat t2.c
> int foo() {
>   return 42;
> }
>
> $ clang t.c t2.c -o t && ./t ; echo $?
> 42
>
> So, we got the definition of foo from t2.c.  If t2.c hadn't been
linked,
> foo would be null.
>
>
> On Mon, Feb 10, 2014 at 6:28 AM, Carl <name.is.carl at gmail.com>
wrote:
>
>>
>> Hello,
>>
>> I'm generating C code (and the resulting obj files) using llvm 3.4
for
>> both unix and windows.
>> And I use the dreaded weak references, that, for windows, are not too
>> widely supported.
>>
>> When I link my application on linux, I have no issue.
>> But when I'm doing the same on windows using mingw I got a
duplicate
>> symbol error :
>>
>>
..\robovm-0.0.8\lib\robovm-rt.jar\dalvik\system\BlockGuard$BlockGuardPolicyException.class.o:(.text$dalvik_system_BlockGuard$24BlockGuardPolicyException_getPolicy__I_lookup[_dalvik_system_BlockGuard$24BlockGuardPolicyException_getPolicy__I_lookup]+0x0):
>> multiple definition of
>>
`dalvik_system_BlockGuard$24BlockGuardPolicyException_getPolicy__I_lookup'
>> ..\Temp\robovm3774596063679264132.tmp\linker.o:(.text+0x340): first
>> defined here
>>
..\robovm-0.0.8\lib\robovm-rt.jar\dalvik\system\BlockGuard$BlockGuardPolicyException.class.o:(.text$dalvik_system_BlockGuard$24BlockGuardPolicyException_getPolicyViolation__I_lookup[_dalvik_system_BlockGuard$24BlockGuardPolicyException_getPolicyViolation__I_lookup]+0x0):
>> multiple definition of
>>
`dalvik_system_BlockGuard$24BlockGuardPolicyException_getPolicyViolation__I_lookup'
>> ..\Temp\robovm3774596063679264132.tmp\linker.o:(.text+0x350): first
>> defined here
>>
..\robovm-0.0.8\lib\robovm-rt.jar\dalvik\system\BlockGuard$BlockGuardPolicyException.class.o:(.text$dalvik_system_BlockGuard$24BlockGuardPolicyException_getMessage__Ljava_lang_String$3B_lookup[_dalvik_system_BlockGuard$24BlockGuardPolicyException_getMessage__Ljava_lang_String$3B_lookup]+0x0):
>> multiple definition of
>>
`dalvik_system_BlockGuard$24BlockGuardPolicyException_getMessage__Ljava_lang_String$3B_lookup'
>>
>> Because those symbols are declared as weak.
>>
>> What is the status about the support of weak symbols on windows?
>> Are they supposed to work? Are they supposed to *never *work ?
>>
>> Do you know any way to fix this (or work around it). I use weak symbols
>> everywhere in my code generation, so I would prefer a fix that
doesn't
>> involve to rewrite my code.
>>
>> I'm considering rewriting the obj files using objcopy.
>> Has this any chance to work ?
>> Here are the o.
>>
>> Cheers,
>> Carl.
>>
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
>>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20140211/107d2df2/attachment.html>