llvm dev - Aug 2007 - [LLVMdev] Strange error of llvm-ld

> I think I have experienced this when more than one module
> contains definitions for the same values. ie. it should only
> be a declaration in one of them.
Hmm, when I compile and link this with plain gcc, it everything 
works.

Anyway, llvm-ld should probably not just say "Cannot link 
file 'blah'", but why it cannot link it.

I compiled llvm in with --enable-debug. Is there any switch that 
I can use to turn on some verbosity, so that I can maybe see 
from debug output where the problem is?

Holger,

I have just committed a patch to cause the linker to properly propagate
error messages from the LinkModules method up to higher levels of the
linker. With this change it should tell you with more detail what is
going on (why it couldn't link the file in). Please update, rebuild and
try again.  If you think the error message is wrong after that, please
file a bug for this. 

To get verbose information, use the -v option on llvm-ld.  In general,
you can find options from any llvm tool with "tool --help".

Thanks,

Reid.

On Thu, 2007-08-16 at 08:35 +0200, Holger Schurig wrote:
> > I think I have experienced this when more than one module
> > contains definitions for the same values. ie. it should only
> > be a declaration in one of them.
> 
> Hmm, when I compile and link this with plain gcc, it everything 
> works.
> 
> Anyway, llvm-ld should probably not just say "Cannot link 
> file 'blah'", but why it cannot link it.
> 
> I compiled llvm in with --enable-debug. Is there any switch that 
> I can use to turn on some verbosity, so that I can maybe see 
> from debug output where the problem is?
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

> I have just committed a patch to cause the linker to properly
> propagate error messages from the LinkModules method up to
> higher levels of the linker.
That helped. The strange error message is:

$ llvm-ld -v -stats -native -O1 -strip-all -o main \
  .obj/conf.o .obj/configwriter.o \
  -L/usr/share/qt3/lib -L/usr/X11R6/lib \
  -lcrypto -lusb -lutil -lqt-mt -lXext -lX11 -lm -lpthread

  Linking bitcode file '.obj/conf.o'
  Linked in file '.obj/conf.o'
  Linking bitcode file '.obj/configwriter.o'
llvm-ld: error: Cannot link file '.obj/configwriter.o': Linking
functions named 'strcmp': symbols have different visibilities!

Now, this happens when I compile the two source files
with "--fvisibility=hidden". If I omit this option, then llvm-ld
happily links those two files.

I made .o files with and without --fvisibility=hidden for both
files. One thing to note is that both versions emit the same
code for the strcmp:

$ grep strcmp *.ll
conf.hidden.o.ll:	%tmp13 = tail call i32 @strcmp( i8* %tmp11, i8* %name )		;
<i32> [#uses=1]
conf.hidden.o.ll:declare i32 @strcmp(i8*, i8*)
conf.hidden.o.ll:	%tmp421 = tail call i32 @strcmp( i8* %tmp11, i8* getelementptr
([6 x i8]* @.str5, i32 0, i32 0) )		; <i32> [#uses=1]
conf.normal.o.ll:	%tmp13 = tail call i32 @strcmp( i8* %tmp11, i8* %name )		;
<i32> [#uses=1]
conf.normal.o.ll:declare i32 @strcmp(i8*, i8*)
conf.normal.o.ll:	%tmp421 = tail call i32 @strcmp( i8* %tmp11, i8* getelementptr
([6 x i8]* @.str5, i32 0, i32 0) )		; <i32> [#uses=1]
configwriter.hidden.o.ll:	%tmp434 = call i32 @strcmp( i8* %tmp411, i8* %tmp394 )
; <i32> [#uses=1]
configwriter.hidden.o.ll:declare i32 @strcmp(i8*, i8*)
configwriter.normal.o.ll:	%tmp434 = call i32 @strcmp( i8* %tmp411, i8* %tmp394 )
; <i32> [#uses=1]
configwriter.normal.o.ll:declare i32 @strcmp(i8*, i8*)