[jira] [Assigned] (KUDU-2068) Kudu/Centos 7/devtoolset miscompilation

["Adar Dembo (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/KUDU-2068?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Adar Dembo reassigned KUDU-2068:
--------------------------------

    Assignee: Adar Dembo

> Kudu/Centos 7/devtoolset miscompilation
> ---------------------------------------
>
>                 Key: KUDU-2068
>                 URL: https://issues.apache.org/jira/browse/KUDU-2068
>             Project: Kudu
>          Issue Type: Bug
>          Components: build
>    Affects Versions: 1.4.0
>            Reporter: Dan Burkert
>            Assignee: Adar Dembo
>
> There are a number of issues related to building Kudu on Centos/RHEL 7 with devtoolset, and on Centos/RHEL 7 machines with devtoolset installed (but not enabled).
> A couple of bits of background info:
> 1) RHEL 7 ships with system GCC/libstdcxx version 4.8.
> 2) devtoolset-3 ships with GCC/libstdcxx version 4.9.
> 3) devtoolset-6 ships with GCC/libstdcxx version 6.2.
> 4) GCC incompatibly changed the {{unordered_set}} and {{unordered_map}} ABIs between libstdcxx version 4.8 and 4.9.  In 4.8, {{sizeof(unordered_set<int>)}} is 48 bytes, whereas in 4.9 and above it is 56 bytes (and similarly for {{unordered_map}}).
> 5) Clang will automatically search for devtoolset installations, and if found, use those headers as opposed to the system headers.
> 6) Clang 4.0 (the current version bundled by Kudu) will find devtoolset versions [up to devtoolset-4|https://github.com/llvm-mirror/clang/blob/release_40/lib/Driver/ToolChains.cpp#L1445-L1449]. The next version of Clang (Clang 5) will find devtoolset version [up to devtoolset-6|https://github.com/llvm-mirror/clang/blob/9a973f3ee99d42a283cafc26407f081daaa8ac21/lib/Driver/ToolChains/Gnu.cpp#L1717-L1720].
> 7) G++ compilers provided by a devtoolset will use the libstdcxx headers provided by that devtoolset.
> 8) Among other things, Kudu uses its bundled clang to pre-compile C++ source files into clang bitcode. One of the classes included in this pre-compilation is kudu::Schema, which includes an {{unordered_set}} field.
> As a result, with certain configurations, the precompiled codegen will cause crashes at runtime:
> Kudu compiled with system gcc on a Centos 7 machine with devtoolset-3 installed: Kudu will be compiled against the system headers, where {{unordered_set}} is 48 bytes. The precompiled code will be compiled by clang against the devtoolset-3 headers, where {{unordered_set}} is 56 bytes.  This results in runtime crashes when calling in to codegenerated functions (codegen-test segfaults reliably).
> Kudu compiled with devtoolset-6 gcc on Centos7: Kudu will be compiled against the devtoolset-6 headers, where {{unordered_set}} is 54 bytes. The precompiled code will be compiled by clang against the system headers, where {{unordered_set}} is 48 bytes (clang 4.0 will not find the devtoolset-6 installation). This results in runtime crashes when calling in to code generated functions (codegen-test segfaults reliably).
> Passing the {{\-gcc-toolchain}} flag to clang with a value appropriate for the currently enabled g++ when precompiling sources will fix this issue, but I haven't found a clean way to figure out how to determine the 'correct' value as part of a script.  For system gcc the value should be {{/usr}}, and for devtoolset-6 the value should be {{/opt/rh/devtoolset-6/root/usr}}.  This corresponds to the {{--prefix}} flag value under the configure flags that {{gcc -v}} spits out, so maybe we can parse it from that.
> Another option is to replace {{unordered_set}}/{{unordered_map}} fields in any objects passed through codegen boundaries, but obviously this is brittle (and there may be other types out there whose ABI is similarly unstable).
> Finally, I'll note that this issue is a good reason why we should maintain the no-c++11 types in public-APIs rule that we currently follow with the client.  Also related: [devtoolset ABI guarantees|https://access.redhat.com/documentation/en-US/Red_Hat_Developer_Toolset/6/html/User_Guide/sect-GCC-CPP.html#sect-GCC-CPP-Compatibility].



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