[LLVMdev] high bit of function address set incorrectly?

Reid Kleckner reid.kleckner at gmail.com
Sun Jul 31 08:31:13 PDT 2011

Are you running in the JIT?  If not, what assembler are you using?
This looks like an issue with encoding the relative PC distance
between the call site and the call entry.

Notice that the call site is at a very high address (0x7fffff....)
while the target is very low.  x86_64 can't encode a full 64-bit
immediate offset in the call instruction, so depending on how you are
generating this code either you or some code you depend on needs to be
jumping through some extra hoops to make this work.


On Sun, Jul 31, 2011 at 8:42 AM, Maurice Gittens
<mainmanmauricio at gmail.com> wrote:
> Hi,
> I recently updated to current llvm svn and fixed-up the minor compiler
> errors I encountered.
> However, at run-time even my Hello world programs crash with a
> segmentation fault.
> A concrete program that crashes on my Linux x86_64 Fedora box is:
> declare void @__ot_runtime_print_int(i8*, i32)
> define void @main() {
> entry:
>  call void @__ot_runtime_print_int(i8* null, i32 12)
>  br label %return
> return:                                           ; preds = %entry
>  ret void
> }
> LLVM magic turns this into the assember shown in the attached image.
> I am no expert but is seems to me that the address generated
> (0x8000012c1eea) for the __ot_runtime_print_int function is incorrect.
> As both  nm and the debugger (kdbg) suggest that the address of the
> function in question is: 0x12c1eea.
> So why is the high bit of the function address set? Anybody willing to
> shed some light on what is happening here?
> Thanks,
> Maurice
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