[llvm] r339027 - Fix raw_fd_ostream::write_impl hang due to an infinite loop with large output

[Owen Reynolds via llvm-commits]

Hi David,

As this only affects large write attempts and a test failure would result
in a hang, I was unsure how best to test this. Any suggestions would be
appreciated.

Thanks,

Owen

On Tue, Aug 7, 2018 at 4:55 AM, David Blaikie <dblaikie at gmail.com> wrote:

> Any chance of a test case?
>
> On Mon, Aug 6, 2018 at 9:22 AM Owen Reynolds via llvm-commits <
> llvm-commits at lists.llvm.org> wrote:
>
>> Author: gbreynoo
>> Date: Mon Aug  6 09:21:41 2018
>> New Revision: 339027
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=339027&view=rev
>> Log:
>> Fix raw_fd_ostream::write_impl hang due to an infinite loop with large
>> output
>>
>> On windows when raw_fd_ostream::write_impl calls write, a 32 bit input is
>> required for character count. As a variable with size_t is used for this
>> argument, on x64 integral demotion occurs. In the case of large files an
>> infinite loop follows.
>> See: https://bugs.llvm.org/show_bug.cgi?id=37926
>> This fix allows the output of files larger than the previous int32 limit.
>>
>> Differential Revision: https://reviews.llvm.org/D48948
>>
>> Modified:
>>     llvm/trunk/lib/Support/raw_ostream.cpp
>>
>> Modified: llvm/trunk/lib/Support/raw_ostream.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/
>> Support/raw_ostream.cpp?rev=339027&r1=339026&r2=339027&view=diff
>> ============================================================
>> ==================
>> --- llvm/trunk/lib/Support/raw_ostream.cpp (original)
>> +++ llvm/trunk/lib/Support/raw_ostream.cpp Mon Aug  6 09:21:41 2018
>> @@ -613,10 +613,10 @@ void raw_fd_ostream::write_impl(const ch
>>    assert(FD >= 0 && "File already closed.");
>>    pos += Size;
>>
>> -  // The maximum write size is limited to SSIZE_MAX because a write
>> -  // greater than SSIZE_MAX is implementation-defined in POSIX.
>> -  // Since SSIZE_MAX is not portable, we use SIZE_MAX >> 1 instead.
>> -  size_t MaxWriteSize = SIZE_MAX >> 1;
>> +  // The maximum write size is limited to INT32_MAX. A write
>> +  // greater than SSIZE_MAX is implementation-defined in POSIX,
>> +  // and Windows _write requires 32 bit input.
>> +  size_t MaxWriteSize = INT32_MAX;
>>
>>  #if defined(__linux__)
>>    // It is observed that Linux returns EINVAL for a very large write
>> (>2G).
>>
>>
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>
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