This is the mail archive of the mailing list for the GCC project.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: Linux doesn't follow x86/x86-64 ABI wrt direction flag

On Wed, Mar 05, 2008 at 11:58:34AM -0800, Joe Buck wrote:
> Aurelien Jarno wrote:
> > >Since version 4.3, gcc changed its behaviour concerning the x86/x86-64 
> > >ABI and the direction flag, that is it now assumes that the direction 
> > >flag is cleared at the entry of a function and it doesn't clear once 
> > >more if needed.
> > >...
> > >I guess this has to be fixed on the kernel side, but also gcc-4.3 could
> > >revert back to the old behaviour, that is clearing the direction flag
> > >when entering a routine that touches it until most people are running a
> > >fixed kernel.
> On Wed, Mar 05, 2008 at 08:00:42AM -0800, H. Peter Anvin wrote:
> > Linux should definitely follow the ABI.  This is a bug, and a pretty 
> > serious such.
> Unfortunately, there are a lot of kernels out there already with this
> problem, and the symptoms are likely to be subtle.  So even if it is true
> that it is the kernel that is "in the wrong", I think we still are going
> to need to give users a workaround from the gcc side as well.
> So I think gcc at least needs an *option* to revert to the old behavior,
> and there's a good argument to make it the default for now, at least for
> x86/x86-64 on Linux.

And for other kernels. I tested OpenBSD 4.1, FreeBSD 6.3, NetBSD 4.0,
they have the same behaviour as Linux, that is they don't clear DF
before calling the signal handler.

I also tested Hurd, and it causes a kernel crash.

  .''`.  Aurelien Jarno	            | GPG: 1024D/F1BCDB73
 : :' :  Debian developer           | Electrical Engineer
 `. `'         |
   `- |

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]