[lkml]   [2007]   [Oct]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: Is gcc thread-unsafe?

On Fri, 26 Oct 2007, Andrew Haley wrote:
> Bart Van Assche writes:
> > Andrew, do you know whether gcc currently contains any optimization
> > that interchanges the order of accesses to non-volatile variables
> > and function calls ?
> It sure does.

Note that doing so is perfectly fine.

But only for local variables that haven't had their addresses taken.

The fact is, those kinds of variables really *are* special. They are
provably not accessible from any other context, and re-ordering them (or
doing anything AT ALL to them - the most basic and very important
optimization is caching them in registers, of course) is always purely an
internal compiler issue.

But if gcc re-orders functions calls with *other* memory accesses, gcc is
totally broken. I doubt it does that. It would break on all but the most
trivial programs, and it would be a clear violation of even standard C.

HOWEVER: the bug that started this thread isn't even "reordering
accesses", it's *adding* accesses that weren't there (and please don't mix
this up with "volatile", since volatile is a totally unrelated issue and
has nothing what-so-ever to do with anything).

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2007-10-26 19:29    [W:0.081 / U:8.844 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site