text: [
  ]
  ASF GitHub Bot commented on DRILL-5050:
  ---------------------------------------
  Github user parthchandra commented on a diff in the pull request:
  --- Diff: contrib/native/client/readme.boost ---
  @@ -0,0 +1.
  + */
  +
  +Building Boost for Dill on MacOs
  +--------------------------------
  +
  +These instreuctions are using Boost version 1.60.0 which is recommended
  --- End diff --
  fixed
  > C++ client library has symbol resolution issues when loaded by a process that already
  uses boost::asio
  > ------------------------------------------------------------------------------------------------------
  >
  > Key: DRILL-5050
  > URL:
  > Project: Apache Drill
  > Issue Type: Bug
  > Components: Client - C++
  > Affects Versions: 1.6.0
  > Environment: MacOs
  > Reporter: Parth Chandra
  > Assignee: Parth Chandra
  > Fix For: 2.0.0
  >
  >
  > h4. Summary
  > On MacOS, the Drill ODBC driver hangs when loaded by any process that might also be using
  {{boost::asio}}. This is observed in trying to connect to Drill via the ODBC driver using
  Tableau.
  > h4. Analysis
  > The problem is seen in the Drill client library on MacOS. In the method
  > {code}
  > DrillClientImpl::recvHandshake
  > .
  > .
  > m_io_service.reset();
  > if (DrillClientConfig::getHandshakeTimeout() > 0){
  > m_deadlineTimer.expires_from_now(boost::posix_time::seconds(DrillClientConfig::getHandshakeTimeout()));
  > m_deadlineTimer.async_wait(boost::bind(
  > &DrillClientImpl::handleHShakeReadTimeout,
  > this,
  > boost::asio::placeholders::error
  > ));
  > DRILL_MT_LOG(DRILL_LOG(LOG_TRACE) << "Started new handshake wait timer
  with "
  > << DrillClientConfig::getHandshakeTimeout() << " seconds."
  << std::endl;)
  > }
  > async_read(
  > this->m_socket,
  > boost::asio::buffer(m_rbuf, LEN_PREFIX_BUFLEN),
  > boost::bind(
  > &DrillClientImpl::handleHandshake,
  > this,
  > m_rbuf,
  > boost::asio::placeholders::error,
  > boost::asio::placeholders::bytes_transferred)
  > );
  > DRILL_MT_LOG(DRILL_LOG(LOG_DEBUG) << "DrillClientImpl::recvHandshake: async
  read waiting for server handshake response.\n";)
  > m_io_service.run();
  > .
  > .
  > {code}
  > The call to {{io_service::run}} returns without invoking any of the handlers that have
  been registered. The {{io_service}} object has two tasks in its queue, the timer task, and
  the socket read task. However, in the run method, the state of the {{io_service}} object appears
  to change and the number of outstanding tasks becomes zero. The run method therefore returns
  immediately. Subsequently, any query request sent to the server hangs as data is never pulled
  off the socket.
  > This is bizarre behaviour and typically points to build problems.
  > More investigation revealed a more interesting thing. {{boost::asio}} is a header only
  library. In other words, there is no actual library {{libboost_asio}}. All the code is included
  into the binary that includes the headers of {{boost::asio}}. It so happens that the Tableau
  process has a library (libtabquery) that uses {{boost::asio}} so the code for {{boost::asio}}
  is already loaded into process memory. When the drill client library (via the ODBC driver)
  is loaded by the loader, the drill client library loads its own copy of the {{boost:asio}}
  code. At runtime, the drill client code jumps to an address that resolves to an address inside
  the libtabquery copy of {{boost::asio}}. And that code returns incorrectly.
  > Really? How is that even allowed? Two copies of {{boost::asio}} in the same process?
  Even if that is allowed, since the code is included at compile time, calls to the {{boost::asio}}
  library should be resolved using internal linkage. And if the call to {{boost::asio}} is not
  resolved statically, the dynamic loader would encounter two symbols with the same name and
  would give us an error. And even if the linker picks one of the symbols, as long as the code
  is the same (for example if both libraries use the same version of boost) can that cause a
  problem? Even more importantly, how do we fix that?
  > h4. Some assembly required
  > The disassembled libdrillClient shows this code inside recvHandshake
  > {code}
  > 000000000003dd8f movq -0xb0(%rbp), %rdi
  > 000000000003dd96 addq $0xc0, %rdi
  > 000000000003dd9d callq 0x1bff42 ## symbol stub for: __ZN5boost4asio10io_service3runEv
  > 000000000003dda2 movq -0xb0(%rbp), %rdi
  > 000000000003dda9 cmpq $0x0, 0x190(%rdi)
  > 000000000003ddb4 movq %rax, -0x158(%rbp)
  > {code}
  > and later in the code
  > {code}
  > 0000000000057216 retq
  > 0000000000057217 nopw (%rax,%rax)
  > __ZN5boost4asio10io_service3runEv: ## definition of io_service::run
  > 0000000000057220 pushq %rbp
  > 0000000000057221 movq %rsp, %rbp
  > 0000000000057224 subq $0x30, %rsp
  > 0000000000057228 leaq -0x18(%rbp), %rax
  > 000000000005722c movq %rdi, -0x8(%rbp)
  > 0000000000057230 movq -0x8(%rbp), %rdi
  > 0000000000057234 movq %rdi, -0x28(%rbp)
  > {code}
  > Note that in recvHandshake the call instruction jumps to an address that is an offset
  (0x1bff42). This offset happens to be beyond the end of the library. It certainly isn't the
  offset at which the io_service::run method is defined (0x57220).
  > The linker is definitely not resolving the address statically, but we had already guessed
  that. It is, in fact, jumping to a stub method and at runtime this address is being resolved
  to the address of the {{io_service::run}} method in libtabquery.
  > Just to check, in the debugger, we can see the following two implementations of {{io_service::run}}
  in the process
  > {code}
  > libtabquery.dylib`boost::asio::io_service::run():
  > 0x10d597a10: pushq %rbp
  > 0x10d597a11: movq %rsp, %rbp
  > 0x10d597a14: pushq %rbx
  > 0x10d597a15: subq $0x18, %rsp
  > 0x10d597a19: movq %rdi, %rbx
  > 0x10d597a1c: movl $0x0, -0x18(%rbp)
  > 0x10d597a23: callq 0x10d5b73a4 ; symbol stub for: boost::system::system_category()
  > 0x10d597a28: movq %rax, -0x10(%rbp)
  > 0x10d597a2c: movq 0x8(%rbx), %rdi
  > 0x10d597a30: leaq -0x18(%rbp), %rsi
  > 0x10d597a34: callq 0x10d5b71e2 ; symbol stub for: boost::asio::detail::task_io_service::run(boost::system::error_code&)
  > 0x10d597a39: cmpl $0x0, -0x18(%rbp)
  > 0x10d597a3d: jne 0x10d597a46 ; boost::asio::io_service::run() +
  54
  > 0x10d597a3f: addq $0x18, %rsp
  > 0x10d597a43: popq %rbx
  > 0x10d597a44: popq %rbp
  > 0x10d597a45: retq
  > 0x10d597a46: leaq -0x18(%rbp), %rdi
  > 0x10d597a4a: callq 0x10d5b71a6 ; symbol stub for: boost::asio::detail::do_throw_error(boost::system::error_code
  const&)
  > 0x10d597a4f: nop
  > libdrillClient.dylib`boost::asio::io_service::run() at io_service.ipp:57:
  > 0x11f158300: pushq %rbp
  > 0x11f158301: movq %rsp, %rbp
  > 0x11f158304: subq $0x30, %rsp
  > 0x11f158308: leaq -0x18(%rbp), %rax
  > 0x11f15830c: movq %rdi, -0x8(%rbp)
  > 0x11f158310: movq -0x8(%rbp), %rdi
  > 0x11f158314: movq %rdi, -0x28(%rbp)
  > 0x11f158318: movq %rax, %rdi
  > 0x11f15831b: callq 0x11f2c210c ; symbol stub for: boost::system::error_code::error_code()
  > 0x11f158320: leaq -0x18(%rbp), %rsi
  > 0x11f158324: movq -0x28(%rbp), %rax
  > 0x11f158328: movq 0x8(%rax), %rdi
  > 0x11f15832c: callq 0x11f2c3516 ; symbol stub for: boost::asio::detail::task_io_service::run(boost::system::error_code&)
  > 0x11f158331: leaq -0x18(%rbp), %rdi
  > 0x11f158335: movq %rax, -0x20(%rbp)
  > 0x11f158339: callq 0x11f2c1bf6 ; symbol stub for: boost::asio::detail::throw_error(boost::system::error_code
  const&)
  > 0x11f15833e: movq -0x20(%rbp), %rax
  > 0x11f158342: addq $0x30, %rsp
  > 0x11f158346: popq %rbp
  > 0x11f158347: retq
  > {code}
  > As suspected, the code for the two versions of {{io_service::run}} is different, so if
  the code is executing the wrong version, then the behaviour will be, expectedly, unexpected.
  > h4. What does not work
  > Linking statically with boost has no effect. The code is inlined in the first place and
  is effectively part of the dynamic library already.
  > Changing the load order of the libraries (by specifying LD_LIBRARY_PATH/DYLD_LIBRARY_PATH
  does not help). This is because the application library is already loaded into the process.
  > The linker -prebind flag does not help. The prebind flag is intended to tell the linker
  to resolve all addresses at link time. Why this did not work is not clear.
  >
  > Both libtabquery.dylib and libdrillClient.dylib contain symbols (functions) from the
  {{boost::asio package}}. At runtime, the MacOs loader assigns the drillClient library to call
  the functions defined in libtabquery. This causes the code to behave unpredictably and eventually
  the ODBC driver 'hangs' waiting for data from the server.
  >
  > Because the symbol linkage is being determined at runtime, changing the linker settings
  in the Drill client build has no effect. This is true even if you build with static linkage
  (a remarkable feature of MacOS!). Also, the boost builds between libtabquery and libdrillClient
  are different even if we use the same boost version; the compiled code is different. This
  is a critical part of the problem because if the compiled code were the same there would be
  no problem if the code was called using the libtabquery version instead of the libdrillClient
  version.
  >
  > h4. Solution
  > The only way to resolve this is to use a 'shaded' version of boost in the drill client
  library. Luckily for us C++ namespaces, boost's bcp tool, and CMake together provide a way
  to rename the boost namespace to any name we like and use it in the drill client code. This
  effectively renames every symbol from boost to a different name using a new namespace name
  and the symbol name conflict does not arise.
  > Using this build of boost, and using static linking (just to make sure) in the Drill
  client library, one is able to connect to and run queries against Drill from Tableau.
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