Maurice Gittens
2011-Jul-31 12:42 UTC
[LLVMdev] high bit of function address set incorrectly?
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
-------------- next part --------------
A non-text attachment was scrubbed...
Name: disassemble.png
Type: image/png
Size: 9049 bytes
Desc: not available
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20110731/621fca5b/attachment.png>
Reid Kleckner
2011-Jul-31 15:31 UTC
[LLVMdev] high bit of function address set incorrectly?
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. Reid 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 > > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev > >
Maurice Gittens
2011-Jul-31 15:59 UTC
[LLVMdev] high bit of function address set incorrectly?
Hi Reid, On Sun, Jul 31, 2011 at 5:31 PM, Reid Kleckner <reid.kleckner at gmail.com> wrote:> 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.Yes, I am running in the JIT. The call site is a jitted function while the function called is not jitted but linked into the executable. This all worked fine until a recent update to current svn.> > 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.I am a quite novice LLVM person, so I simply setup the LLVM datastructures and let it do the magic. Can you point me to where in the LLVM code the encoding of the call offset is determined? It seems something must have changed in this area to make it suddenly stop working. Thanks. Kind regards, Maurice> > Reid > > 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 >> >> _______________________________________________ >> LLVM Developers mailing list >> LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu >> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev >> >> >
Maurice Gittens
2011-Aug-02 18:55 UTC
[LLVMdev] high bit of function address set incorrectly?
Any hints? Maurice On Sun, Jul 31, 2011 at 2:42 PM, 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 >
Maurice Gittens
2011-Aug-05 13:02 UTC
[LLVMdev] high bit of function address set incorrectly?
Hi, The llvm::ExecutionEngine::createJIT has a 'CodeModel' enum parameter taking values: JITDefault, Small, Kernel, Medium or Large. An appropriate value for this parameter fixes the my problem. Kind regards, Maurice On Sun, Jul 31, 2011 at 2:42 PM, 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 >