[LLVMdev] Exception handling question

[Bill Wendling]

On Jan 21, 2010, at 3:50 PM, James Williams wrote:

> Hi,
> 
> I'm trying to get exception handling working in my compiler targetting LLVM. I've been working from the LLVM exception handling documentation (including http://llvm.org/docs/ExceptionHandling.html and http://wiki.llvm.org/HowTo:_Build_JIT_based_Exception_mechanism) and looking at g++-llvm's output.
> 
> I've been trying to get a minimal test function to work, which simply invokes _Unwind_RaiseException with a single clean-up landing pad. However. when I run it my personality function is not getting called - _Unwind_RaiseException simply returns apparently doing nothing. Looking at the x86-64 assembly output from llc, I can see this is happening because the personality function is not getting into the DWARF eh table (the landing pad is there though). 
> 
> I'm stumped as to why not. I'd be grateful if anyone can point out what I'm doing wrong here:
> 
> define i32 @_ZN4N0014Main5test5EN2IO6WriterEiA_l(%6*, %4*, i32, %33*) {
> entry:
>   %err = alloca %4*                               ; <%4**> [#uses=1]
>   %count = alloca i32                             ; <i32*> [#uses=1]
>   %e = alloca %33*                                ; <%33**> [#uses=2]
>   %this = alloca %6*                              ; <%6**> [#uses=1]
>   %.ex_value = alloca i8*                         ; <i8**> [#uses=1]
>   %.ex_value_l = alloca i8*                       ; <i8**> [#uses=0]
>   %.ex_type = alloca i64                          ; <i64*> [#uses=1]
>   br label %4
> 
> ; <label>:4                                       ; preds = %entry
>   store %6* %0, %6** %this
>   store %4* %1, %4** %err
>   store i32 %2, i32* %count
>   store %33* %3, %33** %e
>   br label %.try_body
> 
> .try_body:                                        ; preds = %4
>   %5 = load %33** %e                              ; <%33*> [#uses=1]
>   %6 = getelementptr inbounds %33* %5, i32 0, i32 2, i32 0 ; <i64*> [#uses=1]
>   %7 = invoke i8* (...)* bitcast (i32 (%struct._Unwind_Exception*)* @_Unwind_RaiseException to i8* (...)*)(i64* %6)
>           to label %8 unwind label %.finally_pad  ; <i8*> [#uses=0]
> 
> ; <label>:8                                       ; preds = %.try_body
>   br label %.finally_handler
> 
> .finally_pad:                                     ; preds = %.try_body
>   %9 = call i8* @llvm.eh.exception()              ; <i8*> [#uses=2]
>   store i8* %9, i8** %.ex_value
>   %10 = call i64 (i8*, i8*, ...)* @llvm.eh.selector.i64(i8* %9, i8* bitcast (i32 (i32, i32, i64, %struct._Unwind_Exception*, %struct._Unwind_Context*)* @__l_personality to i8*)) ; <i64> [#uses=1]

I think you'll need a "i8* null" at the end of this @llvm.eh.selector.i64 call.

-bw

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