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base repository: emscripten-core/emscripten
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  • 1 commit
  • 1 file changed
  • 1 contributor

Commits on Oct 8, 2016

  1. Fix Exception Handling Leak and Crash 

    This patch fixes two issues in the exception handling backend
(transforms actual results reported below to expected results
reported below).

Environment:
  Branch: master
  Emcc -v: emcc (Emscripten gcc/clang-like replacement + linker
           emulating GNU ld) 1.36.0
           clang version 3.9.0
           (https://github.com/kripken/emscripten-fastcomp-clang/
           271ce598c3d1fe74efadc254f5be1b57edea9f41)
           (https://github.com/kripken/emscripten-fastcomp/
           61acfb230665464544f2e8db292f8999fc3c628c)
           (emscripten 1.36.0 : 1.36.0)
           Target: x86_64-apple-darwin16.0.0
           Thread model: posix
           InstalledDir: /Users/ray/src/gm/emsdk_portable/clang/
           fastcomp/build_master_64/bin
           INFO:root:(Emscripten: Running sanity checks)

Issue 1: Re-thrown exceptions leak (and their destructors are
         not invoked)

Repro:

 #include <iostream>

struct NeedsCleanUp
{
    NeedsCleanUp()
    {
        std::cout << "Creating cleanup item" << std::endl;
    }

    ~NeedsCleanUp()
    {
        std::cout << "Destroying cleanup item" << std::endl;
    }
};

int main(int argc, char* argv[])
{
    try
    {
        try
        {
            throw NeedsCleanUp {};
        }
        catch (...)
        {
            throw;  // rethrow causes leak
        }
    }
    catch (...)
    {
    }

    return 0;
}

Build and run:
em++ -g -std=c++11 --emrun -s EXCEPTION_DEBUG=0 -o exc1.html exc1.cpp
emrun --browser chrome exc1.html

ACTUAL RESULT:

pre-main prep time: 23 ms
Creating cleanup item

ACTUAL RESULT WITH EXCEPTION DEBUG:

pre-main prep time: 25 ms
Creating cleanup item
Compiled code throwing an exception, 5267520,8,357
can_catch on 5267520
cxa_begin_catch 5267520,stack,5267520
addref 5267520
Compiled code RE-throwing an exception, popped 5267520,5267520,stack,
can_catch on 5267520
cxa_begin_catch 5267520,stack,5267520
addref 5267520
cxa_end_catch popped 5267520,5267520,stack,
decref 5267520

EXPECTED RESULT:

pre-main prep time: 23 ms
Creating cleanup item
Destroying cleanup item

EXPECTED RESULT WITH EXCEPTION DEBUG:

pre-main prep time: 24 ms
Creating cleanup item
Compiled code throwing an exception, 5267520,8,357
can_catch on 5267520
cxa_begin_catch 5267520,stack,5267520
addref 5267520
Compiled code RE-throwing an exception, popped 5267520,5267520,stack,
  5267520
can_catch on 5267520
cxa_end_catch popped 5267520,5267520,stack,
decref 5267520
cxa_begin_catch 5267520,stack,5267520
addref 5267520
cxa_end_catch popped 5267520,0,stack,
decref 5267520
Destroying cleanup item
decref freeing exception 5267520,0,stack,

=======================================================================

Issue 2: Resuming exception unwinding causes crash when resumed
         exceptions have multiple references

Repro:

 #include <iostream>

struct NeedsCleanUp
{
    const int item;

    NeedsCleanUp(int i)
        : item { i }
    {
        std::cout << "Creating cleanup item " << item << std::endl;
    }

    NeedsCleanUp(const NeedsCleanUp& src)
        : item { 100 + src.item }
    {
        std::cout << "Copying cleanup item " << src.item << " to "
                  << item << std::endl;
    }

    ~NeedsCleanUp()
    {
        std::cout << "Destroying cleanup item " << item << std::endl;
    }
};

int main(int argc, char* argv[])
{
    NeedsCleanUp ex { 1 };
    std::exception_ptr exp1 { std::make_exception_ptr(ex) };
    std::exception_ptr exp2 { exp1 };

    try
    {
        [&exp1] {
            NeedsCleanUp cl { 2 };  // causes "resuming exception"
                                    // ref count reset
            std::rethrow_exception(exp1);
        } ();
    }
    catch (...)
    {
    }

    return 0;
}

Build and run:
em++ -g -std=c++11 --emrun -s EXCEPTION_DEBUG=0 -o exc2.html exc2.cpp
emrun --browser chrome exc2.html

ACTUAL RESULT:

pre-main prep time: 23 ms
Creating cleanup item 1
Copying cleanup item 1 to 101
Copying cleanup item 101 to 201
Destroying cleanup item 101
Creating cleanup item 2
Destroying cleanup item 2
Destroying cleanup item 201
exception thrown: TypeError: Cannot read property 'refcount' of
  undefined,TypeError: Cannot read property 'refcount' of undefined
    at Object.decRef (http://localhost:6931/exc2.js:1564:20)
    at ___cxa_decrement_exception_refcount
       (http://localhost:6931/exc2.js:1578:18)
    at __ZNSt13exception_ptrD2Ev (http://localhost:6931/exc2.js:23642:2)
    at _main (http://localhost:6931/exc2.js:5993:3)
    at Object.asm._main (http://localhost:6931/exc2.js:65981:19)
    at Object.callMain (http://localhost:6931/exc2.js:66150:30)
    at doRun (http://localhost:6931/exc2.js:66208:60)
    at http://localhost:6931/exc2.js:66219:7

ACTUAL RESULT WITH EXCEPTION DEBUG:

pre-main prep time: 22 ms
Creating cleanup item 1
Copying cleanup item 1 to 101
Copying cleanup item 101 to 201
Compiled code throwing an exception, 5267520,8,360
can_catch on 5267520
cxa_begin_catch 5267520,stack,5267520
addref 5267520
addref 5267520
cxa_end_catch popped 5267520,5267520,stack,
decref 5267520
Destroying cleanup item 101
addref 5267520
Creating cleanup item 2
addref 5267520
Compiled code RE-throwing an exception, popped 5267520,0,stack,
can_catch on 5267520
decref 5267520
Destroying cleanup item 2
Resuming exception 5267520,5267520
can_catch on 5267520
cxa_begin_catch 5267520,stack,5267520
addref 5267520
decref 5267520
Destroying cleanup item 201
decref freeing exception 5267520,5267520,stack,5267520
no de-adjustment for unknown exception ptr 5267520
decref 5267520
exception thrown: TypeError: Cannot read property 'refcount' of
  undefined,TypeError: Cannot read property 'refcount' of undefined
    at Object.decRef (http://localhost:6931/exc2.js:1568:20)
    at ___cxa_decrement_exception_refcount
       (http://localhost:6931/exc2.js:1583:18)
    at __ZNSt13exception_ptrD2Ev (http://localhost:6931/exc2.js:23654:2)
    at _main (http://localhost:6931/exc2.js:6005:3)
    at Object.asm._main (http://localhost:6931/exc2.js:65993:19)
    at Object.callMain (http://localhost:6931/exc2.js:66162:30)
    at doRun (http://localhost:6931/exc2.js:66220:60)
    at http://localhost:6931/exc2.js:66231:7

EXPECTED RESULT:

pre-main prep time: 22 ms
Creating cleanup item 1
Copying cleanup item 1 to 101
Copying cleanup item 101 to 201
Destroying cleanup item 101
Creating cleanup item 2
Destroying cleanup item 2
Destroying cleanup item 201
Destroying cleanup item 1

EXPECTED RESULT WITH EXCEPTION DEBUG:

pre-main prep time: 27 ms
Creating cleanup item 1
Copying cleanup item 1 to 101
Copying cleanup item 101 to 201
Compiled code throwing an exception, 5267520,8,360
can_catch on 5267520
cxa_begin_catch 5267520,stack,5267520
addref 5267520
addref 5267520
cxa_end_catch popped 5267520,5267520,stack,
decref 5267520
Destroying cleanup item 101
addref 5267520
Creating cleanup item 2
addref 5267520
Compiled code RE-throwing an exception, popped 5267520,0,stack,5267520
can_catch on 5267520
decref 5267520
Destroying cleanup item 2
Resuming exception 5267520,5267520
can_catch on 5267520
cxa_begin_catch 5267520,stack,5267520,5267520
addref 5267520
cxa_end_catch popped 5267520,5267520,stack,5267520
decref 5267520
decref 5267520
decref 5267520
Destroying cleanup item 201
decref freeing exception 5267520,0,stack,5267520
Destroying cleanup item 1
    @rbit
    rbit committed Oct 8, 2016
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