[LLVMdev] llvm-ld support of native libraries

[Reid Spencer]

On Mon, 2007-05-07 at 23:45 -0500, Ryan M. Lefever wrote:
> What is the current status of llvm-ld's support of native libraries?  

It should be working. We've fixed some issues with correct detection of
object/archive/shared object files in the last few weeks.

> I 
> have a bytecode file that needs to link against librt.so.  So, I ran:
> 
> llvm-ld -native -o x.exe x.bc -L/usr/lib64 -lrt
> 
> and I get the following error:
> 
> /tmp/ccB7DGu1.o(.text+0x1a3): In function `main':
> : undefined reference to `clock_gettime'
> /tmp/ccB7DGu1.o(.text+0x6d8): In function `main':
> : undefined reference to `clock_gettime'
> collect2: ld returned 1 exit status

Have you verified that librt.so is in /usr/lib64 and that it contains
clock_gettime? This looks like a standard undefined reference message
meaning you haven't supplied sufficient arguments to llvm-ld to link the
program. Does a similar command line with gcc work?
> 
> Is that error occurring because llvm-ld does not support native 
> libraries. 

No. Its occurring because the clock_gettime symbol can't be found. Note
that llvm-ld invokes the native linker (via gcc) to do the actual native
linking. 

>  I am able to use llc to turn x.bc into native assembly and 
> gcc to link the natively assembly against librt.so to get an executable, 
> but I was going to use the llvm native backend if possible.

That's another way to do it, but the way you described above should work
as well and should, in fact, do the same thing. That is, when you link
as given above, llvm-ld will:

1. convert x.bc into x.s via llc
2. assemble llc using gcc (which punts it to gas)
3. link using gcc with something like gcc -o x.exe x.o -L/usr/lib64 -lrt

Reid.

> 
> Regards,
> Ryan
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