[PATCH] D48948: Fix raw_fd_ostream::write_impl hang due to an infinite loop with large output

[Owen Reynolds via Phabricator via llvm-commits]

gbreynoo added inline comments.


================
Comment at: lib/Support/raw_ostream.cpp:617-618
+#ifdef _WIN64
+  // Windows write() requires signed 32 bit input so SIZE_MAX can not be used 
+  size_t MaxWriteSize = _I32_MAX;
+#else
----------------
zturner wrote:
> Doesn't it actually require 32-bit unsigned input?
> 
> https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/write
> 
> ```
> int _write(
>    int fd,
>    const void *buffer,
>    unsigned int count
> );
> ```
I'll clarify this in the comment above. 
Although the input type for _write is unsigned, the return type is signed ("-1" is returned in cases of an error). This is checked for in line 642. As the standard return of _write is to return how many bytes are written, in the case this value is larger than the signed max, the return value is a negative value. If the maximum unsigned value is written this will be -1 and indicate an error.

As the comment below states, windows _write is following POSIX as the behaviour for a write greater than SSIZE_MAX is implementation defined. I think it's best to keep to the portable behaviour below and not write anything windows specific to allow for a larger than SSIZE_MAX write. 


Repository:
  rL LLVM

https://reviews.llvm.org/D48948