_Unwind_Backtrace() can't get past functions with EH.


Bugzilla Link	PR21053
Status	NEW
Importance	P normal
Reported by	Microsoft Office (asg.msft@gmail.com)
Reported on	2014-09-24 05:21:11 -0700
Last modified on	2014-09-24 06:04:02 -0700
Version	3.4
Hardware	PC Windows NT
CC	dgregor@apple.com, llvm-bugs@lists.llvm.org
Fixed by commit(s)
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Blocked by
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Clang 3.4
Picked up from: From Android r9d NDK.

Description:
First issue:
When the functions don't have try-catch in them the back trace (code given
below which uses _Unwind_Backtrace() and _Unwind_GetIP()) works fine and the IP
gets updated and prints all the functions walking down the stack.

Whereas if any of the functions have a try-catch block, _Unwind_GetIP() can't
get past that function. So it keeps looping around that IP indefinitely.

Second issue: The return code for _Unwind_Backtrace() is _URC_FAILURE.

I'm not sure whether the main trunk clang has the same issue. But Android's
NDK's clang definitely reproduces this. I filed a bug for Android as well.

Compilation command:
clang++.exe -target armv7-none-linux-androideabi -O0 -g -funwind-tables -
fexceptions -fno-omit-frame-pointer  -std=c++11 -c foo.cpp -o foo.o

Sample code: foo.cpp:

#include <unwind.h>

_Unwind_Reason_Code trace_func(struct _Unwind_Context *context, void* arg)
{
   void *ip = (void *)_Unwind_GetIP(context);
   if(nullptr == ip)
       // ip is never nullptr. Further if the context is from a function
       // that has try-catch block, it can't move beyond that frame.
    return _URC_END_OF_STACK;
   else
   return _URC_NO_REASON;
}

void func3()
{
    _Unwind_Backtrace(trace_func, nullptr);
}

void func2() {
    try { func3(); }
    catch(...){}
}
void func1() { func2(); }

int main()
{
    func1();
    return 0;
}

EXPECTED RESULTS:
For the above program I expect the stack back trace to be (of course once I
resolve the symbols with dladdr):
_Unwind_Backtrace
func3()
func2()
func1()
main()
...

ACTUAL RESULTS:
_Unwind_Backtrace
func3()
func2()
func2()
func2()
ad infinitum

When I remove the try-catch though, it works fine and reports the results as in
EXPECTED results above. Please let me know if you need more details.

Thanks.

Quuxplusone / LLVMBugzillaTest

_Unwind_Backtrace() can't get past functions with EH. #21052