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Re: Inquiry about GCC Summer Of Code project idea.

From: Ian Lance Taylor
Subject: Re: Inquiry about GCC Summer Of Code project idea.
Date: Tue, 30 Apr 2013 06:58:05 -0700

On Tue, Apr 30, 2013 at 6:53 AM, Thomas Schwinge
<thomas@codesourcery.com> wrote:
> On <http://darnassus.sceen.net/~hurd-web/open_issues/gccgo/> I have just
> updated/posted a getcontext/makecontext/setcontext/swapcontext usage
> analysis.  This might constitute a "road block": the Hurd currently does
> not allow for changing the stack of a process/thread.  Implemented a
> while before TLS/__thread variables came along, we have a legacy
> threadvar mechanism implemented in glibc, which places thread-local
> variables (errno, for example) at the bottom of a thread's stack.  Then,
> when switching the stack of a thread, glibc can't locate these anymore,
> and "bad things" happen.  This threadvar mechanism is scheduled to go
> away (we do implement TLS by now), but when working on that I hit "some
> issues" and have not yet found the time to continue.
> <http://darnassus.sceen.net/~hurd-web/open_issues/glibc/t/tls-threadvar/>
> and
> <http://news.gmane.org/find-root.php?message_id=%3c878vdyqht3%2Efsf%40kepler%2Eschwinge%2Ehomeip%2Enet%3e>
> have the details.
> Now, it seems the GCC Go port is implemented in a way that makes
> extensive use of switching stacks.  So until this threadvar issue is
> resolved, there is probably no way to really proceed with the GCC Go port
> for GNU Hurd -- unless maybe this stack switching could be hacked around
> (Ian?), say, by limiting oneself to not using Goroutines and similar
> "specials", and having a custom/minimal Go runtime startup.

Go does require switching stacks.  A port of Go that doesn't support
goroutines would be useless--nothing in the standard library would
work.  It might be possible to use pthread_getspecific and friends
instead of TLS.


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