On 02/03/2010 09:13 AM, David Miller wrote: > From: Arnd Bergmann <arnd@xxxxxxxx> > Date: Wed, 3 Feb 2010 18:06:27 +0100 > >>> But if the consensus is that we should fix this properly I can >>> replace the patch with one introducing a compat_sys_personality >>> which only gets used for compat tasks. >> >> Right now, sparc64 and powerpc64 use sys32_personality for both native >> and compat tasks, x86 never uses it and all others use it only for >> compat tasks. That seems more sensible if we keep this function at >> all. > > If it only gets used for compat tasks, you can only switch in > one direction. I think it needs to be handled for both compat > and non-compat tasks, in order to allow for that. That seems odd... with the wrapper you can ever only switch in one direction, and if you use it for non-compat tasks you wouldn't be ever to switch back, period. > That's why powerpc64 and sparc64 do things the way they do, > I am pretty sure. As far as I can tell, the ppc64 and sparc64 implementations would seem to be trapdoors from which no return is possible. That's a pretty defensible position in some ways -- it mimics the 32-bit machine even down to the personality() syscall -- but it definitely has disadvantages. The x86 method of simply not bothering doesn't seem to have caused problems -- our compat (and noncompat) tasks happily return PER_LINUX32 if that is the mode and we don't seem to have had complaints with it. If userspace ever had an issue with it -- and they might have, at one point in history libc used to call personality() during startup, which it doesn't seem to anymore -- they presumably have worked through it. As such, I'm more than a little reluctant to change the current behavior. -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
