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Christian Schafmeister

2015-Apr-12 04:58 UTC

[LLVMdev] Looking for advice on how to debug a problem with C++ style exception handling code that my compiler generates.

Logan,

I need to make a correction of the post that preceded this one!

I was wrong when I said this:> When I load the bitcode file for this module and then dump it just before
it is JITted, the “uwtable” attribute has disappeared - is this prune-eh doing
its work even though it’s not listed above in the list of function pass
managers?
The “uwtable” attribute does not disappear!   I had forgotten to llvm-as the .ll
file that I was hand-editing. (I’ve hacked my compiler so that it JITs a module
from a bitcode file that I hand edit while I’m trying to sort out whether these
attributes can be properly set to avoid the problem that I’m seeing).

I’m trying different combinations of function attributes to see if that fixes
the problem.

Best,

.Chris.

On Apr 12, 2015, at 12:51 AM, Christian Schafmeister <chris.schaf at
verizon.net> wrote:
> Logan,
> 
> Thank you very much for the feedback and guidance.
> 
> The passes that I use for JIT compilation are as follows - I don’t see
prune-eh in there - could it still be happening?
> 
> (defun create-function-pass-manager-for-compile (module)
>   (let ((fpm (llvm-sys:make-function-pass-manager module)))
>     (llvm-sys:function-pass-manager-add fpm
(llvm-sys:create-basic-alias-analysis-pass))   ;; <<< passes start here
>     (llvm-sys:function-pass-manager-add fpm
(llvm-sys:create-instruction-combining-pass))
>     (llvm-sys:function-pass-manager-add fpm
(llvm-sys:create-promote-memory-to-register-pass))
>     (llvm-sys:function-pass-manager-add fpm
(llvm-sys:create-reassociate-pass))
>     (llvm-sys:function-pass-manager-add fpm (llvm-sys:create-gvnpass nil))
>     (llvm-sys:function-pass-manager-add fpm
(llvm-sys:create-cfgsimplification-pass -1))
>     (llvm-sys:do-initialization fpm)
>     fpm))
> 
> I set things up to add the “uwtable” function attribute to every function
that I generate - a current module looks like this: 
https://gist.github.com/drmeister/107a84d3d5023ebf13a8
> On line 617 is the function (now it has the "uwtable" attribute)
that is not propagating an exception thrown in cc_call on line 642.
> 
> A couple of questions:  the prototype for cc_call on line 559 has the
function attribute “nounwind” - I should probably remove that - correct?
> 
> When I load the bitcode file for this module and then dump it just before
it is JITted, the “uwtable” attribute has disappeared - is this prune-eh doing
its work even though it’s not listed above in the list of function pass
managers?
> 
> I feel like there may be multiple things going on, thwarting my attempts to
get these functions to propagate an exception.
> 
> Thanks,
> 
> .Chris.
> 
> 
> On Apr 11, 2015, at 11:03 PM, Logan Chien <tzuhsiang.chien at
gmail.com> wrote:
> 
>> Hi Christian,
>> 
>> Thanks for your explanation.  I know your situation now.  I would
suggest you to check the optimization pass used by the JIT compiler, especially
IPO/PruneEH.cpp.  It will try to add nounwind attribute to functions which will
result in the problem you have mentioned earlier.
>> 
>> Alternatively, as a workaround, try to add uwtable (function attribute)
to the functions that are generated by your compiler.  This may help as well.
>> 
>> Sincerely,
>> Logan
>> 
>> On Sun, Apr 12, 2015 at 8:49 AM, Christian Schafmeister <chris.schaf
at verizon.net> wrote:
>> Logan,
>> 
>> There may be some confusion here because I wasn’t completely clear
about what was calling what and where “invoke” appeared to be necessary when I
JIT the code and where I realize that “invoke” is absolutely necessary.    As
far as I understand the Itanium ABI I only need an “invoke” in function A when
function B is invoked - the rest of the calls to C() and D() should be able to
use “call".
>> 
>> 
>> Here’s an example in C++ (for illustration) and then the identical
example in Common Lisp.
>> 
>> In Common Lisp I can compile individual expressions in the REPL.  
>> Here is a more illustrative example.   If I compile all of these
functions ahead of time - everything works fine and D() and C() are called using
LLVM “call”.
>> But if I JIT these functions one at a time it will fail.  If I use llvm
“invoke” to JIT the function C() - then the thrown exception will make it to A()
and everything works.
>> 
>> // In C++
>> //
>> void D() {
>>     throw MyException();
>> };
>> 
>> void C() {
>>     D();    // This should be able to be called with “call” 
>> 		// - but if I JIT this function it won’t work - I need “invoke” and a
dummy landing pad
>> };
>> 
>> void B() {
>>     C();    // This can be called with "call"
>> };
>> 
>> 
>> void A() {
>>     try {
>>         B();     // <<--- This needs to be called with
"invoke"
>>     } catch ( MyException& e) {
>> 	/* Do something */
>>     };
>> };
>> 
>> 
>> In Common Lisp:
>> 
>> (defun d ()
>>  (throw 'Exception nil))
>> 
>> (defun c ()
>>   (d))    ; <-- This can be called with llvm “call” but if I JIT
this function it will fail!  I need to use “invoke”!
>> 
>> (defun b ()
>>   (c))    ; <-- This can be called with llvm "call"
>> 
>> (defun a ()
>>   (catch 'exception
>>     (b)))   ; <-- This needs to called with llvm “invoke"
>> 
>> 
>> 
>> On Apr 11, 2015, at 8:15 PM, Logan Chien <tzuhsiang.chien at
gmail.com> wrote:
>> 
>>> Hi Christian,
>>> 
>>> > I don’t see anything in the Itanium ABI that says I need to
call the function that throws an exception with “invoke” to get exception
handling to work!
>>> 
>>> AFAICT, it is the design of LLVM IR and its implementation.  To
catch the exceptions thrown by the callee functions, we should use the invoke
instruction along with the landingpad instruction.  If you are calling a
function with a call instruction, the LLVM backend will simply assumes frame
unwinding when the callee throws an exception.
>>> 
>>> 
>>> FYI, according to LLVM reference manual, an invoke-instruction has
following semantics:
>>> The ‘invoke‘ instruction causes control to transfer to a specified
function, with the possibility of control flow transfer to either the ‘normal‘
label or the ‘exception‘ label. If the callee function returns with the “ret”
instruction, control flow will return to the “normal” label. If the callee (or
any indirect callees) returns via the “resume” instruction or other exception
handling mechanism, control is interrupted and continued at the dynamically
nearest “exception” label.
>>> 
>>> OTOH, here's the description for call instruction: 
>>> The ‘call‘ instruction represents a simple function call.
>>> 
>>> 
>>> Hope this is helpful.
>>> 
>>> Best regards,
>>> Logan
>>> 
>>> On Sun, Apr 12, 2015 at 6:33 AM, Christian Schafmeister
<chris.schaf at verizon.net> wrote:
>>> 
>>> It appears that I've found a very curious effect where if I JIT
a function that throws an exception and I use "call" to call it the
throw fails despite there being a "catch" clause on the stack. But if
I use “invoke” it works fine!
>>> 
>>>  If I call the function (@cc_invoke) that throws a
“core::CatchThrow” exception like this:
>>> call void @cc_invoke({ {}*, i64 }* %result-ptr, {}* %3, i64 2, {}*
%4, {}* %5, {}* null, {}* null, {}* null)
>>> ;; Comment out the next two lines and   
>>> ;    to label %return0 unwind label %landing-pad1
>>> ;return0:
>>> ret void
>>>  
>>> landing-pad1:                                     ; No
predecessors!
>>>   %6 = landingpad { i8*, i32 } personality i32 (...)*
@__gxx_personality_v0
>>>           cleanup
>>>   resume { i8*, i32 } %6
>>> }
>>> 
>>> It fails with: libc++abi.dylib: terminating with uncaught exception
of type core::CatchThrow
>>> 
>>> If instead I convert the “call” into an “invoke” and hook in a
dummy landing-pad like this:
>>> 
>>> invoke void @cc_invoke({ {}*, i64 }* %result-ptr, {}* %3, i64 2,
{}* %4, {}* %5, {}* null, {}* null, {}* null)
>>>     to label %return0 unwind label %landing-pad1
>>> return0:
>>>   ret void
>>>  
>>> landing-pad1:                                     ; No
predecessors!
>>>   %6 = landingpad { i8*, i32 } personality i32 (...)*
@__gxx_personality_v0
>>>           cleanup
>>>   resume { i8*, i32 } %6
>>> }
>>> 
>>> The CatchThrow exception is caught and everything works fine!  I
don’t need to call the caller or any outer function with “invoke” except for in
the function that has the landing pad that recognizes core::CatchThrow.
>>> 
>>> I don’t see anything in the Itanium ABI that says I need to call
the function that throws an exception with “invoke” to get exception handling to
work!
>>> 
>>> Does anyone have any ideas what I might be doing wrong?
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> On Apr 9, 2015, at 6:59 PM, Lang Hames <lhames at gmail.com>
wrote:
>>> 
>>>> Hi Christian,
>>>> 
>>>> Andy's already covered the major points, but you could
consider filing a bug at http://llvm.org/bugs too, especially if you've got
a small test-case that demonstrates the issue. Exception handling hasn't
been a priority in the past, but as more people adopt LLVM's JIT APIs I
suspect it will get more attention, and bug reports will help us figure out what
needs doing.
>>>> 
>>>> Cheers,
>>>> Lang.
>>>> 
>>>> On Thu, Apr 9, 2015 at 11:43 AM, Kaylor, Andrew
<andrew.kaylor at intel.com> wrote:
>>>> Hi Christian,
>>>> 
>>>>  
>>>> 
>>>> I suspect that at least some of the details depend on what
platform you’re working on.  I believe that MCJIT attempts to register eh frame
information for either MachO or ELF objects (though for some ELF platforms
nothing actually happens).  What happens to it after that is a darker area, at
least for me.
>>>> 
>>>>  
>>>> 
>>>> Apparently there was a GDB command that did just what you want
-- “info catch” -- but I had never used it and it has been removed.  It’s too
bad because it sounds like a nice feature.  It was supposed to dump a list of
catch handlers for whatever frame you’re looking at.  I suspect, however, that
it would have just confirmed that your catch handler isn’t properly hooked up
without being helpful in figuring out why.
>>>> 
>>>>  
>>>> 
>>>> You could try debugging the RuntimeDyld code that registers eh
frames and see if that looks right.  RuntimeDyld::registerEHFrames() might be a
helpful starting point.
>>>> 
>>>>  
>>>> 
>>>> -Andy
>>>> 
>>>>  
>>>> 
>>>>  
>>>> 
>>>> From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at
cs.uiuc.edu] On Behalf Of Christian Schafmeister
>>>> Sent: Wednesday, April 08, 2015 10:09 PM
>>>> To: LLVM Developers Mailing List
>>>> Subject: [LLVMdev] Looking for advice on how to debug a problem
with C++ style exception handling code that my compiler generates.
>>>> 
>>>>  
>>>> 
>>>>  
>>>> 
>>>> Hi,
>>>> 
>>>>  
>>>> 
>>>> I’m looking for advice on how to debug a problem with my
exception handling code.
>>>> 
>>>> I’m asking a specific question here - but general advice on how
to debug something like this would be greatly appreciated.
>>>> 
>>>>  
>>>> 
>>>> Is there any way to get a list of landing pad clauses that are
active at a particular point in a program?
>>>> I'd like to get something like a backtrace but listing all
active landing pad clauses. The typeids of the C++ types
>>>> I'm trying to debug a problem where an exception that
I'm throwing is not being caught.
>>>> 
>>>> I'm generating JITed code with LLVM and landing pads and
I've got shared libraries - lots of things going on that could potentially
be going wrong.
>>>> 
>>>>  
>>>> 
>>>> A list of the pointer values like @_ZTIN4core9DynamicGoE is
what I’m looking for.  Then I could compare that to the typeids that I know
should be in that list.
>>>> 
>>>>  
>>>> 
>>>> "(TRY-0).landing-pad":                            ;
preds = %"(TRY-0).normal-dest14", %"(TRY-0).tagbody-B-1",
%"(TRY-0).normal-dest10", %"(TRY-0).normal-dest9",
%"(TRY-0).normal-dest8", %"(TRY-0).normal-dest",
%"(TRY-0).tagbody-#:G1621-0"
>>>> 
>>>>   %14 = landingpad { i8*, i32 } personality i32 (...)*
@__gxx_personality_v0
>>>> 
>>>>           catch i8* @_ZTIN4core9DynamicGoE
>>>> 
>>>>           catch i8* @_ZTIN4core10ReturnFromE, !dbg !26
>>>> 
>>>>   %15 = extractvalue { i8*, i32 } %14, 0, !dbg !26
>>>> 
>>>>   %16 = extractvalue { i8*, i32 } %14, 1, !dbg !26
>>>> 
>>>>   %17 = call i32 @llvm.eh.typeid.for(i8*
@_ZTIN4core9DynamicGoE), !dbg !26
>>>> 
>>>>   %18 = icmp eq i32 %16, %17, !dbg !26
>>>> 
>>>>   br i1 %18, label %"(TRY-0).handler-block14470",
label %"(TRY-0).dispatch-header19", !dbg !26
>>>> 
>>>>  
>>>> 
>>>> I’m getting this error when I throw a core::Unwind exception
and I’m certain that there is a landing pad with that clause.
>>>> 
>>>>  
>>>> 
>>>> libc++abi.dylib: terminating with uncaught exception of type
core::Unwind
>>>> 
>>>> ../../src/gctools/memoryManagement.cc:75 Trapped SIGABRT -
starting debugger
>>>> 
>>>> ABORT was called!!!!!!!!!!!!
>>>> 
>>>>  
>>>> 
>>>>  
>>>> 
>>>> I’ve written a Common Lisp compiler that uses LLVM as the
backend and it interoperates with C++ code and I use C++ exception handling for
non-local exits.
>>>> 
>>>> 
>>>> _______________________________________________
>>>> LLVM Developers mailing list
>>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>> 
>>>> 
>>> 
>>> 
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>> 
>>> 
>> 
>> 
> 
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Christian Schafmeister

2015-Apr-12 05:09 UTC

head link

[LLVMdev] Looking for advice on how to debug a problem with C++ style exception handling code that my compiler generates.

I’ve tried every reasonable combination of disabling nounwind and enabling
uwtable - it doesn’t fix the problem.

Here is a copy of the most recent Module with the uwtable attribute attached to
cc_call and the function that doesn’t propagate the exception
“cl->UNNAMED-LAMBDA”

https://gist.github.com/drmeister/b97dec956c6ee9ffeb75



On Apr 12, 2015, at 12:58 AM, Christian Schafmeister <chris.schaf at
verizon.net> wrote:
> Logan,
> 
> I need to make a correction of the post that preceded this one!
> 
> I was wrong when I said this:
>> When I load the bitcode file for this module and then dump it just
before it is JITted, the “uwtable” attribute has disappeared - is this prune-eh
doing its work even though it’s not listed above in the list of function pass
managers?
> 
> The “uwtable” attribute does not disappear!   I had forgotten to llvm-as
the .ll file that I was hand-editing. (I’ve hacked my compiler so that it JITs a
module from a bitcode file that I hand edit while I’m trying to sort out whether
these attributes can be properly set to avoid the problem that I’m seeing).
> 
> I’m trying different combinations of function attributes to see if that
fixes the problem.
> 
> Best,
> 
> .Chris.
> 
> On Apr 12, 2015, at 12:51 AM, Christian Schafmeister <chris.schaf at
verizon.net> wrote:
> 
>> Logan,
>> 
>> Thank you very much for the feedback and guidance.
>> 
>> The passes that I use for JIT compilation are as follows - I don’t see
prune-eh in there - could it still be happening?
>> 
>> (defun create-function-pass-manager-for-compile (module)
>>   (let ((fpm (llvm-sys:make-function-pass-manager module)))
>>     (llvm-sys:function-pass-manager-add fpm
(llvm-sys:create-basic-alias-analysis-pass))   ;; <<< passes start here
>>     (llvm-sys:function-pass-manager-add fpm
(llvm-sys:create-instruction-combining-pass))
>>     (llvm-sys:function-pass-manager-add fpm
(llvm-sys:create-promote-memory-to-register-pass))
>>     (llvm-sys:function-pass-manager-add fpm
(llvm-sys:create-reassociate-pass))
>>     (llvm-sys:function-pass-manager-add fpm (llvm-sys:create-gvnpass
nil))
>>     (llvm-sys:function-pass-manager-add fpm
(llvm-sys:create-cfgsimplification-pass -1))
>>     (llvm-sys:do-initialization fpm)
>>     fpm))
>> 
>> I set things up to add the “uwtable” function attribute to every
function that I generate - a current module looks like this: 
https://gist.github.com/drmeister/107a84d3d5023ebf13a8
>> On line 617 is the function (now it has the "uwtable"
attribute) that is not propagating an exception thrown in cc_call on line 642.
>> 
>> A couple of questions:  the prototype for cc_call on line 559 has the
function attribute “nounwind” - I should probably remove that - correct?
>> 
>> When I load the bitcode file for this module and then dump it just
before it is JITted, the “uwtable” attribute has disappeared - is this prune-eh
doing its work even though it’s not listed above in the list of function pass
managers?
>> 
>> I feel like there may be multiple things going on, thwarting my
attempts to get these functions to propagate an exception.
>> 
>> Thanks,
>> 
>> .Chris.
>> 
>> 
>> On Apr 11, 2015, at 11:03 PM, Logan Chien <tzuhsiang.chien at
gmail.com> wrote:
>> 
>>> Hi Christian,
>>> 
>>> Thanks for your explanation.  I know your situation now.  I would
suggest you to check the optimization pass used by the JIT compiler, especially
IPO/PruneEH.cpp.  It will try to add nounwind attribute to functions which will
result in the problem you have mentioned earlier.
>>> 
>>> Alternatively, as a workaround, try to add uwtable (function
attribute) to the functions that are generated by your compiler.  This may help
as well.
>>> 
>>> Sincerely,
>>> Logan
>>> 
>>> On Sun, Apr 12, 2015 at 8:49 AM, Christian Schafmeister
<chris.schaf at verizon.net> wrote:
>>> Logan,
>>> 
>>> There may be some confusion here because I wasn’t completely clear
about what was calling what and where “invoke” appeared to be necessary when I
JIT the code and where I realize that “invoke” is absolutely necessary.    As
far as I understand the Itanium ABI I only need an “invoke” in function A when
function B is invoked - the rest of the calls to C() and D() should be able to
use “call".
>>> 
>>> 
>>> Here’s an example in C++ (for illustration) and then the identical
example in Common Lisp.
>>> 
>>> In Common Lisp I can compile individual expressions in the REPL.  
>>> Here is a more illustrative example.   If I compile all of these
functions ahead of time - everything works fine and D() and C() are called using
LLVM “call”.
>>> But if I JIT these functions one at a time it will fail.  If I use
llvm “invoke” to JIT the function C() - then the thrown exception will make it
to A() and everything works.
>>> 
>>> // In C++
>>> //
>>> void D() {
>>>     throw MyException();
>>> };
>>> 
>>> void C() {
>>>     D();    // This should be able to be called with “call” 
>>> 		// - but if I JIT this function it won’t work - I need “invoke”
and a dummy landing pad
>>> };
>>> 
>>> void B() {
>>>     C();    // This can be called with "call"
>>> };
>>> 
>>> 
>>> void A() {
>>>     try {
>>>         B();     // <<--- This needs to be called with
"invoke"
>>>     } catch ( MyException& e) {
>>> 	/* Do something */
>>>     };
>>> };
>>> 
>>> 
>>> In Common Lisp:
>>> 
>>> (defun d ()
>>>  (throw 'Exception nil))
>>> 
>>> (defun c ()
>>>   (d))    ; <-- This can be called with llvm “call” but if I JIT
this function it will fail!  I need to use “invoke”!
>>> 
>>> (defun b ()
>>>   (c))    ; <-- This can be called with llvm "call"
>>> 
>>> (defun a ()
>>>   (catch 'exception
>>>     (b)))   ; <-- This needs to called with llvm “invoke"
>>> 
>>> 
>>> 
>>> On Apr 11, 2015, at 8:15 PM, Logan Chien <tzuhsiang.chien at
gmail.com> wrote:
>>> 
>>>> Hi Christian,
>>>> 
>>>> > I don’t see anything in the Itanium ABI that says I need
to call the function that throws an exception with “invoke” to get exception
handling to work!
>>>> 
>>>> AFAICT, it is the design of LLVM IR and its implementation.  To
catch the exceptions thrown by the callee functions, we should use the invoke
instruction along with the landingpad instruction.  If you are calling a
function with a call instruction, the LLVM backend will simply assumes frame
unwinding when the callee throws an exception.
>>>> 
>>>> 
>>>> FYI, according to LLVM reference manual, an invoke-instruction
has following semantics:
>>>> The ‘invoke‘ instruction causes control to transfer to a
specified function, with the possibility of control flow transfer to either the
‘normal‘ label or the ‘exception‘ label. If the callee function returns with the
“ret” instruction, control flow will return to the “normal” label. If the callee
(or any indirect callees) returns via the “resume” instruction or other
exception handling mechanism, control is interrupted and continued at the
dynamically nearest “exception” label.
>>>> 
>>>> OTOH, here's the description for call instruction: 
>>>> The ‘call‘ instruction represents a simple function call.
>>>> 
>>>> 
>>>> Hope this is helpful.
>>>> 
>>>> Best regards,
>>>> Logan
>>>> 
>>>> On Sun, Apr 12, 2015 at 6:33 AM, Christian Schafmeister
<chris.schaf at verizon.net> wrote:
>>>> 
>>>> It appears that I've found a very curious effect where if I
JIT a function that throws an exception and I use "call" to call it
the throw fails despite there being a "catch" clause on the stack. But
if I use “invoke” it works fine!
>>>> 
>>>>  If I call the function (@cc_invoke) that throws a
“core::CatchThrow” exception like this:
>>>> call void @cc_invoke({ {}*, i64 }* %result-ptr, {}* %3, i64 2,
{}* %4, {}* %5, {}* null, {}* null, {}* null)
>>>> ;; Comment out the next two lines and   
>>>> ;    to label %return0 unwind label %landing-pad1
>>>> ;return0:
>>>> ret void
>>>>  
>>>> landing-pad1:                                     ; No
predecessors!
>>>>   %6 = landingpad { i8*, i32 } personality i32 (...)*
@__gxx_personality_v0
>>>>           cleanup
>>>>   resume { i8*, i32 } %6
>>>> }
>>>> 
>>>> It fails with: libc++abi.dylib: terminating with uncaught
exception of type core::CatchThrow
>>>> 
>>>> If instead I convert the “call” into an “invoke” and hook in a
dummy landing-pad like this:
>>>> 
>>>> invoke void @cc_invoke({ {}*, i64 }* %result-ptr, {}* %3, i64
2, {}* %4, {}* %5, {}* null, {}* null, {}* null)
>>>>     to label %return0 unwind label %landing-pad1
>>>> return0:
>>>>   ret void
>>>>  
>>>> landing-pad1:                                     ; No
predecessors!
>>>>   %6 = landingpad { i8*, i32 } personality i32 (...)*
@__gxx_personality_v0
>>>>           cleanup
>>>>   resume { i8*, i32 } %6
>>>> }
>>>> 
>>>> The CatchThrow exception is caught and everything works fine! 
I don’t need to call the caller or any outer function with “invoke” except for
in the function that has the landing pad that recognizes core::CatchThrow.
>>>> 
>>>> I don’t see anything in the Itanium ABI that says I need to
call the function that throws an exception with “invoke” to get exception
handling to work!
>>>> 
>>>> Does anyone have any ideas what I might be doing wrong?
>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
>>>> On Apr 9, 2015, at 6:59 PM, Lang Hames <lhames at
gmail.com> wrote:
>>>> 
>>>>> Hi Christian,
>>>>> 
>>>>> Andy's already covered the major points, but you could
consider filing a bug at http://llvm.org/bugs too, especially if you've got
a small test-case that demonstrates the issue. Exception handling hasn't
been a priority in the past, but as more people adopt LLVM's JIT APIs I
suspect it will get more attention, and bug reports will help us figure out what
needs doing.
>>>>> 
>>>>> Cheers,
>>>>> Lang.
>>>>> 
>>>>> On Thu, Apr 9, 2015 at 11:43 AM, Kaylor, Andrew
<andrew.kaylor at intel.com> wrote:
>>>>> Hi Christian,
>>>>> 
>>>>>  
>>>>> 
>>>>> I suspect that at least some of the details depend on what
platform you’re working on.  I believe that MCJIT attempts to register eh frame
information for either MachO or ELF objects (though for some ELF platforms
nothing actually happens).  What happens to it after that is a darker area, at
least for me.
>>>>> 
>>>>>  
>>>>> 
>>>>> Apparently there was a GDB command that did just what you
want -- “info catch” -- but I had never used it and it has been removed.  It’s
too bad because it sounds like a nice feature.  It was supposed to dump a list
of catch handlers for whatever frame you’re looking at.  I suspect, however,
that it would have just confirmed that your catch handler isn’t properly hooked
up without being helpful in figuring out why.
>>>>> 
>>>>>  
>>>>> 
>>>>> You could try debugging the RuntimeDyld code that registers
eh frames and see if that looks right.  RuntimeDyld::registerEHFrames() might be
a helpful starting point.
>>>>> 
>>>>>  
>>>>> 
>>>>> -Andy
>>>>> 
>>>>>  
>>>>> 
>>>>>  
>>>>> 
>>>>> From: llvmdev-bounces at cs.uiuc.edu
[mailto:llvmdev-bounces at cs.uiuc.edu] On Behalf Of Christian Schafmeister
>>>>> Sent: Wednesday, April 08, 2015 10:09 PM
>>>>> To: LLVM Developers Mailing List
>>>>> Subject: [LLVMdev] Looking for advice on how to debug a
problem with C++ style exception handling code that my compiler generates.
>>>>> 
>>>>>  
>>>>> 
>>>>>  
>>>>> 
>>>>> Hi,
>>>>> 
>>>>>  
>>>>> 
>>>>> I’m looking for advice on how to debug a problem with my
exception handling code.
>>>>> 
>>>>> I’m asking a specific question here - but general advice on
how to debug something like this would be greatly appreciated.
>>>>> 
>>>>>  
>>>>> 
>>>>> Is there any way to get a list of landing pad clauses that
are active at a particular point in a program?
>>>>> I'd like to get something like a backtrace but listing
all active landing pad clauses. The typeids of the C++ types
>>>>> I'm trying to debug a problem where an exception that
I'm throwing is not being caught.
>>>>> 
>>>>> I'm generating JITed code with LLVM and landing pads
and I've got shared libraries - lots of things going on that could
potentially be going wrong.
>>>>> 
>>>>>  
>>>>> 
>>>>> A list of the pointer values like @_ZTIN4core9DynamicGoE is
what I’m looking for.  Then I could compare that to the typeids that I know
should be in that list.
>>>>> 
>>>>>  
>>>>> 
>>>>> "(TRY-0).landing-pad":                           
; preds = %"(TRY-0).normal-dest14", %"(TRY-0).tagbody-B-1",
%"(TRY-0).normal-dest10", %"(TRY-0).normal-dest9",
%"(TRY-0).normal-dest8", %"(TRY-0).normal-dest",
%"(TRY-0).tagbody-#:G1621-0"
>>>>> 
>>>>>   %14 = landingpad { i8*, i32 } personality i32 (...)*
@__gxx_personality_v0
>>>>> 
>>>>>           catch i8* @_ZTIN4core9DynamicGoE
>>>>> 
>>>>>           catch i8* @_ZTIN4core10ReturnFromE, !dbg !26
>>>>> 
>>>>>   %15 = extractvalue { i8*, i32 } %14, 0, !dbg !26
>>>>> 
>>>>>   %16 = extractvalue { i8*, i32 } %14, 1, !dbg !26
>>>>> 
>>>>>   %17 = call i32 @llvm.eh.typeid.for(i8*
@_ZTIN4core9DynamicGoE), !dbg !26
>>>>> 
>>>>>   %18 = icmp eq i32 %16, %17, !dbg !26
>>>>> 
>>>>>   br i1 %18, label %"(TRY-0).handler-block14470",
label %"(TRY-0).dispatch-header19", !dbg !26
>>>>> 
>>>>>  
>>>>> 
>>>>> I’m getting this error when I throw a core::Unwind
exception and I’m certain that there is a landing pad with that clause.
>>>>> 
>>>>>  
>>>>> 
>>>>> libc++abi.dylib: terminating with uncaught exception of
type core::Unwind
>>>>> 
>>>>> ../../src/gctools/memoryManagement.cc:75 Trapped SIGABRT -
starting debugger
>>>>> 
>>>>> ABORT was called!!!!!!!!!!!!
>>>>> 
>>>>>  
>>>>> 
>>>>>  
>>>>> 
>>>>> I’ve written a Common Lisp compiler that uses LLVM as the
backend and it interoperates with C++ code and I use C++ exception handling for
non-local exits.
>>>>> 
>>>>> 
>>>>> _______________________________________________
>>>>> LLVM Developers mailing list
>>>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>>> 
>>>>> 
>>>> 
>>>> 
>>>> _______________________________________________
>>>> LLVM Developers mailing list
>>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>> 
>>>> 
>>> 
>>> 
>> 
> 
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Christian Schafmeister

2015-Apr-12 05:16 UTC

head link

[LLVMdev] Looking for advice on how to debug a problem with C++ style exception handling code that my compiler generates.

This is the only thing that I’ve found that works in terms of getting the
exception to propagate out of the JITted function - change the “call” to an
“invoke” and hook in the do-nothing landing-pad.

https://gist.github.com/drmeister/7a35046f666826206973

Compare line 646 of the file above to the one that I just posted.
> https://gist.github.com/drmeister/b97dec956c6ee9ffeb75

The first one propagates the exception and the second one fails.




On Apr 12, 2015, at 1:09 AM, Christian Schafmeister <chris.schaf at
verizon.net> wrote:
> I’ve tried every reasonable combination of disabling nounwind and enabling
uwtable - it doesn’t fix the problem.
> 
> Here is a copy of the most recent Module with the uwtable attribute
attached to cc_call and the function that doesn’t propagate the exception
“cl->UNNAMED-LAMBDA”
> 
> https://gist.github.com/drmeister/b97dec956c6ee9ffeb75
> 
> 
> 
> On Apr 12, 2015, at 12:58 AM, Christian Schafmeister <chris.schaf at
verizon.net> wrote:
> 
>> Logan,
>> 
>> I need to make a correction of the post that preceded this one!
>> 
>> I was wrong when I said this:
>>> When I load the bitcode file for this module and then dump it just
before it is JITted, the “uwtable” attribute has disappeared - is this prune-eh
doing its work even though it’s not listed above in the list of function pass
managers?
>> 
>> The “uwtable” attribute does not disappear!   I had forgotten to
llvm-as the .ll file that I was hand-editing. (I’ve hacked my compiler so that
it JITs a module from a bitcode file that I hand edit while I’m trying to sort
out whether these attributes can be properly set to avoid the problem that I’m
seeing).
>> 
>> I’m trying different combinations of function attributes to see if that
fixes the problem.
>> 
>> Best,
>> 
>> .Chris.
>> 
>> On Apr 12, 2015, at 12:51 AM, Christian Schafmeister <chris.schaf at
verizon.net> wrote:
>> 
>>> Logan,
>>> 
>>> Thank you very much for the feedback and guidance.
>>> 
>>> The passes that I use for JIT compilation are as follows - I don’t
see prune-eh in there - could it still be happening?
>>> 
>>> (defun create-function-pass-manager-for-compile (module)
>>>   (let ((fpm (llvm-sys:make-function-pass-manager module)))
>>>     (llvm-sys:function-pass-manager-add fpm
(llvm-sys:create-basic-alias-analysis-pass))   ;; <<< passes start here
>>>     (llvm-sys:function-pass-manager-add fpm
(llvm-sys:create-instruction-combining-pass))
>>>     (llvm-sys:function-pass-manager-add fpm
(llvm-sys:create-promote-memory-to-register-pass))
>>>     (llvm-sys:function-pass-manager-add fpm
(llvm-sys:create-reassociate-pass))
>>>     (llvm-sys:function-pass-manager-add fpm
(llvm-sys:create-gvnpass nil))
>>>     (llvm-sys:function-pass-manager-add fpm
(llvm-sys:create-cfgsimplification-pass -1))
>>>     (llvm-sys:do-initialization fpm)
>>>     fpm))
>>> 
>>> I set things up to add the “uwtable” function attribute to every
function that I generate - a current module looks like this: 
https://gist.github.com/drmeister/107a84d3d5023ebf13a8
>>> On line 617 is the function (now it has the "uwtable"
attribute) that is not propagating an exception thrown in cc_call on line 642.
>>> 
>>> A couple of questions:  the prototype for cc_call on line 559 has
the function attribute “nounwind” - I should probably remove that - correct?
>>> 
>>> When I load the bitcode file for this module and then dump it just
before it is JITted, the “uwtable” attribute has disappeared - is this prune-eh
doing its work even though it’s not listed above in the list of function pass
managers?
>>> 
>>> I feel like there may be multiple things going on, thwarting my
attempts to get these functions to propagate an exception.
>>> 
>>> Thanks,
>>> 
>>> .Chris.
>>> 
>>> 
>>> On Apr 11, 2015, at 11:03 PM, Logan Chien <tzuhsiang.chien at
gmail.com> wrote:
>>> 
>>>> Hi Christian,
>>>> 
>>>> Thanks for your explanation.  I know your situation now.  I
would suggest you to check the optimization pass used by the JIT compiler,
especially IPO/PruneEH.cpp.  It will try to add nounwind attribute to functions
which will result in the problem you have mentioned earlier.
>>>> 
>>>> Alternatively, as a workaround, try to add uwtable (function
attribute) to the functions that are generated by your compiler.  This may help
as well.
>>>> 
>>>> Sincerely,
>>>> Logan
>>>> 
>>>> On Sun, Apr 12, 2015 at 8:49 AM, Christian Schafmeister
<chris.schaf at verizon.net> wrote:
>>>> Logan,
>>>> 
>>>> There may be some confusion here because I wasn’t completely
clear about what was calling what and where “invoke” appeared to be necessary
when I JIT the code and where I realize that “invoke” is absolutely necessary.  
As far as I understand the Itanium ABI I only need an “invoke” in function A
when function B is invoked - the rest of the calls to C() and D() should be able
to use “call".
>>>> 
>>>> 
>>>> Here’s an example in C++ (for illustration) and then the
identical example in Common Lisp.
>>>> 
>>>> In Common Lisp I can compile individual expressions in the
REPL.
>>>> Here is a more illustrative example.   If I compile all of
these functions ahead of time - everything works fine and D() and C() are called
using LLVM “call”.
>>>> But if I JIT these functions one at a time it will fail.  If I
use llvm “invoke” to JIT the function C() - then the thrown exception will make
it to A() and everything works.
>>>> 
>>>> // In C++
>>>> //
>>>> void D() {
>>>>     throw MyException();
>>>> };
>>>> 
>>>> void C() {
>>>>     D();    // This should be able to be called with “call” 
>>>> 		// - but if I JIT this function it won’t work - I need
“invoke” and a dummy landing pad
>>>> };
>>>> 
>>>> void B() {
>>>>     C();    // This can be called with "call"
>>>> };
>>>> 
>>>> 
>>>> void A() {
>>>>     try {
>>>>         B();     // <<--- This needs to be called with
"invoke"
>>>>     } catch ( MyException& e) {
>>>> 	/* Do something */
>>>>     };
>>>> };
>>>> 
>>>> 
>>>> In Common Lisp:
>>>> 
>>>> (defun d ()
>>>>  (throw 'Exception nil))
>>>> 
>>>> (defun c ()
>>>>   (d))    ; <-- This can be called with llvm “call” but if I
JIT this function it will fail!  I need to use “invoke”!
>>>> 
>>>> (defun b ()
>>>>   (c))    ; <-- This can be called with llvm
"call"
>>>> 
>>>> (defun a ()
>>>>   (catch 'exception
>>>>     (b)))   ; <-- This needs to called with llvm
“invoke"
>>>> 
>>>> 
>>>> 
>>>> On Apr 11, 2015, at 8:15 PM, Logan Chien <tzuhsiang.chien at
gmail.com> wrote:
>>>> 
>>>>> Hi Christian,
>>>>> 
>>>>> > I don’t see anything in the Itanium ABI that says I
need to call the function that throws an exception with “invoke” to get
exception handling to work!
>>>>> 
>>>>> AFAICT, it is the design of LLVM IR and its implementation.
To catch the exceptions thrown by the callee functions, we should use the invoke
instruction along with the landingpad instruction.  If you are calling a
function with a call instruction, the LLVM backend will simply assumes frame
unwinding when the callee throws an exception.
>>>>> 
>>>>> 
>>>>> FYI, according to LLVM reference manual, an
invoke-instruction has following semantics:
>>>>> The ‘invoke‘ instruction causes control to transfer to a
specified function, with the possibility of control flow transfer to either the
‘normal‘ label or the ‘exception‘ label. If the callee function returns with the
“ret” instruction, control flow will return to the “normal” label. If the callee
(or any indirect callees) returns via the “resume” instruction or other
exception handling mechanism, control is interrupted and continued at the
dynamically nearest “exception” label.
>>>>> 
>>>>> OTOH, here's the description for call instruction: 
>>>>> The ‘call‘ instruction represents a simple function call.
>>>>> 
>>>>> 
>>>>> Hope this is helpful.
>>>>> 
>>>>> Best regards,
>>>>> Logan
>>>>> 
>>>>> On Sun, Apr 12, 2015 at 6:33 AM, Christian Schafmeister
<chris.schaf at verizon.net> wrote:
>>>>> 
>>>>> It appears that I've found a very curious effect where
if I JIT a function that throws an exception and I use "call" to call
it the throw fails despite there being a "catch" clause on the stack.
But if I use “invoke” it works fine!
>>>>> 
>>>>>  If I call the function (@cc_invoke) that throws a
“core::CatchThrow” exception like this:
>>>>> call void @cc_invoke({ {}*, i64 }* %result-ptr, {}* %3, i64
2, {}* %4, {}* %5, {}* null, {}* null, {}* null)
>>>>> ;; Comment out the next two lines and   
>>>>> ;    to label %return0 unwind label %landing-pad1
>>>>> ;return0:
>>>>> ret void
>>>>>  
>>>>> landing-pad1:                                     ; No
predecessors!
>>>>>   %6 = landingpad { i8*, i32 } personality i32 (...)*
@__gxx_personality_v0
>>>>>           cleanup
>>>>>   resume { i8*, i32 } %6
>>>>> }
>>>>> 
>>>>> It fails with: libc++abi.dylib: terminating with uncaught
exception of type core::CatchThrow
>>>>> 
>>>>> If instead I convert the “call” into an “invoke” and hook
in a dummy landing-pad like this:
>>>>> 
>>>>> invoke void @cc_invoke({ {}*, i64 }* %result-ptr, {}* %3,
i64 2, {}* %4, {}* %5, {}* null, {}* null, {}* null)
>>>>>     to label %return0 unwind label %landing-pad1
>>>>> return0:
>>>>>   ret void
>>>>>  
>>>>> landing-pad1:                                     ; No
predecessors!
>>>>>   %6 = landingpad { i8*, i32 } personality i32 (...)*
@__gxx_personality_v0
>>>>>           cleanup
>>>>>   resume { i8*, i32 } %6
>>>>> }
>>>>> 
>>>>> The CatchThrow exception is caught and everything works
fine!  I don’t need to call the caller or any outer function with “invoke”
except for in the function that has the landing pad that recognizes
core::CatchThrow.
>>>>> 
>>>>> I don’t see anything in the Itanium ABI that says I need to
call the function that throws an exception with “invoke” to get exception
handling to work!
>>>>> 
>>>>> Does anyone have any ideas what I might be doing wrong?
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>> On Apr 9, 2015, at 6:59 PM, Lang Hames <lhames at
gmail.com> wrote:
>>>>> 
>>>>>> Hi Christian,
>>>>>> 
>>>>>> Andy's already covered the major points, but you
could consider filing a bug at http://llvm.org/bugs too, especially if
you've got a small test-case that demonstrates the issue. Exception handling
hasn't been a priority in the past, but as more people adopt LLVM's JIT
APIs I suspect it will get more attention, and bug reports will help us figure
out what needs doing.
>>>>>> 
>>>>>> Cheers,
>>>>>> Lang.
>>>>>> 
>>>>>> On Thu, Apr 9, 2015 at 11:43 AM, Kaylor, Andrew
<andrew.kaylor at intel.com> wrote:
>>>>>> Hi Christian,
>>>>>> 
>>>>>>  
>>>>>> 
>>>>>> I suspect that at least some of the details depend on
what platform you’re working on.  I believe that MCJIT attempts to register eh
frame information for either MachO or ELF objects (though for some ELF platforms
nothing actually happens).  What happens to it after that is a darker area, at
least for me.
>>>>>> 
>>>>>>  
>>>>>> 
>>>>>> Apparently there was a GDB command that did just what
you want -- “info catch” -- but I had never used it and it has been removed. 
It’s too bad because it sounds like a nice feature.  It was supposed to dump a
list of catch handlers for whatever frame you’re looking at.  I suspect,
however, that it would have just confirmed that your catch handler isn’t
properly hooked up without being helpful in figuring out why.
>>>>>> 
>>>>>>  
>>>>>> 
>>>>>> You could try debugging the RuntimeDyld code that
registers eh frames and see if that looks right. 
RuntimeDyld::registerEHFrames() might be a helpful starting point.
>>>>>> 
>>>>>>  
>>>>>> 
>>>>>> -Andy
>>>>>> 
>>>>>>  
>>>>>> 
>>>>>>  
>>>>>> 
>>>>>> From: llvmdev-bounces at cs.uiuc.edu
[mailto:llvmdev-bounces at cs.uiuc.edu] On Behalf Of Christian Schafmeister
>>>>>> Sent: Wednesday, April 08, 2015 10:09 PM
>>>>>> To: LLVM Developers Mailing List
>>>>>> Subject: [LLVMdev] Looking for advice on how to debug a
problem with C++ style exception handling code that my compiler generates.
>>>>>> 
>>>>>>  
>>>>>> 
>>>>>>  
>>>>>> 
>>>>>> Hi,
>>>>>> 
>>>>>>  
>>>>>> 
>>>>>> I’m looking for advice on how to debug a problem with
my exception handling code.
>>>>>> 
>>>>>> I’m asking a specific question here - but general
advice on how to debug something like this would be greatly appreciated.
>>>>>> 
>>>>>>  
>>>>>> 
>>>>>> Is there any way to get a list of landing pad clauses
that are active at a particular point in a program?
>>>>>> I'd like to get something like a backtrace but
listing all active landing pad clauses. The typeids of the C++ types
>>>>>> I'm trying to debug a problem where an exception
that I'm throwing is not being caught.
>>>>>> 
>>>>>> I'm generating JITed code with LLVM and landing
pads and I've got shared libraries - lots of things going on that could
potentially be going wrong.
>>>>>> 
>>>>>>  
>>>>>> 
>>>>>> A list of the pointer values like
@_ZTIN4core9DynamicGoE is what I’m looking for.  Then I could compare that to
the typeids that I know should be in that list.
>>>>>> 
>>>>>>  
>>>>>> 
>>>>>> "(TRY-0).landing-pad":                       
; preds = %"(TRY-0).normal-dest14", %"(TRY-0).tagbody-B-1",
%"(TRY-0).normal-dest10", %"(TRY-0).normal-dest9",
%"(TRY-0).normal-dest8", %"(TRY-0).normal-dest",
%"(TRY-0).tagbody-#:G1621-0"
>>>>>> 
>>>>>>   %14 = landingpad { i8*, i32 } personality i32 (...)*
@__gxx_personality_v0
>>>>>> 
>>>>>>           catch i8* @_ZTIN4core9DynamicGoE
>>>>>> 
>>>>>>           catch i8* @_ZTIN4core10ReturnFromE, !dbg !26
>>>>>> 
>>>>>>   %15 = extractvalue { i8*, i32 } %14, 0, !dbg !26
>>>>>> 
>>>>>>   %16 = extractvalue { i8*, i32 } %14, 1, !dbg !26
>>>>>> 
>>>>>>   %17 = call i32 @llvm.eh.typeid.for(i8*
@_ZTIN4core9DynamicGoE), !dbg !26
>>>>>> 
>>>>>>   %18 = icmp eq i32 %16, %17, !dbg !26
>>>>>> 
>>>>>>   br i1 %18, label
%"(TRY-0).handler-block14470", label
%"(TRY-0).dispatch-header19", !dbg !26
>>>>>> 
>>>>>>  
>>>>>> 
>>>>>> I’m getting this error when I throw a core::Unwind
exception and I’m certain that there is a landing pad with that clause.
>>>>>> 
>>>>>>  
>>>>>> 
>>>>>> libc++abi.dylib: terminating with uncaught exception of
type core::Unwind
>>>>>> 
>>>>>> ../../src/gctools/memoryManagement.cc:75 Trapped
SIGABRT - starting debugger
>>>>>> 
>>>>>> ABORT was called!!!!!!!!!!!!
>>>>>> 
>>>>>>  
>>>>>> 
>>>>>>  
>>>>>> 
>>>>>> I’ve written a Common Lisp compiler that uses LLVM as
the backend and it interoperates with C++ code and I use C++ exception handling
for non-local exits.
>>>>>> 
>>>>>> 
>>>>>> _______________________________________________
>>>>>> LLVM Developers mailing list
>>>>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>>>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>>>> 
>>>>>> 
>>>>> 
>>>>> 
>>>>> _______________________________________________
>>>>> LLVM Developers mailing list
>>>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>>> 
>>>>> 
>>>> 
>>>> 
>>> 
>> 
> 
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