[PATCH] D12689: [libc++][static linking] std streams are not initialized prior to their use in static object constructors

[Evgeny Astigeevich via cfe-commits]

eastig created this revision.
eastig added a subscriber: cfe-commits.

When an executable (e.g. for bare metal environment) is statically linked  with libc++ the following code might not work as expected:

```
#include <iostream>
 
class Foo {
public:
  Foo(int n) {
    std::cout << "Hello World - " << n << std::endl;
  }
};
 
Foo f(5);
 
int main() {
  return 0;
}
```
The program hangs or crashes because 'std::cout' is not initialized before 'Foo f(5)'.

The standard says:

> 27.3 Standard iostream objects
> Header <iostream> synopsis
> (2) ... The objects are constructed, and the associations are established at some time prior to or during first 
> time an object of class basic_ios<charT,traits>::Init is constructed, and in any case before the body of main
> begins execution [264]. The objects are not destroyed during program execution [265].
> 

And footnote 265 says:

> Constructors and destructors for static objects can access these objects to read input from stdin or write output
> to stdout or stderr.

The similar issue was raised more than year ago. A patch was proposed but not committed. See discussion of it here:

[[ http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20130304/075363.html | initial patch ]]
[[ http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20130325/077130.html | review, suggestion for #ifdef ]]

The proposed patch caused initialization/deinitialization of the std streams as many times as the static Init objects were created.
The current patch fixes this issue. A number of uses is counted by means of __shared_count. It is used instead of a 'int' variable because it is thread-safe. The standard allows multi-threaded initialization of static objects from different compilation modules.

 

http://reviews.llvm.org/D12689

Files:
  include/ios
  src/iostream.cpp

-------------- next part --------------
A non-text attachment was scrubbed...
Name: D12689.34198.patch
Type: text/x-patch
Size: 3390 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20150908/eaff58ce/attachment.bin>