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

[Justin Bogner via cfe-dev]

Please ping patches on cfe-commits, not -dev.

> On Sep 10, 2015, at 05:36, Evgeny Astigeevich via cfe-commits <cfe-commits at lists.llvm.org> wrote:
> 
> Ping.
> Could anyone review the patch?
> 
> Kind regards,
> Evgeny Astigeevich
> 
> -----Original Message-----
> From: Evgeny Astigeevich [mailto:evgeny.astigeevich at arm.com]
> Sent: 08 September 2015 11:00
> To: Evgeny Astigeevich
> Cc: cfe-commits at lists.llvm.org
> Subject: [PATCH] D12689: [libc++][static linking] std streams are not initialized prior to their use in static object constructors
> 
> 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
> 
> 
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