Re: [PATCH] x86_64 signal handling for 64-bit apps w/ mixed 32-bit code - trivial fix

[Andi Kleen <ak@suse.de>]

Bryan Ford <baford@mit.edu> writes:

> The proposed patch doesn't affect any performance-critical paths (e.g., 
> syscall or interrupt entry/exit), and merely involves a couple more moves 
> to/from user space on signal frame setup and sigreturn.  It also doesn't 
> affect the size or shape of the sigcontext at all, since there already was an
> (unused) slot for CS, and I've assigned the convenient __pad0 field as a slot 
> for SS.  The existing, unused slots for FS and GS remain unused for now, and 
> I don't see any urgent need to change that.  The only way this might break an 
> existing app is if the app tries to cons up its own signal frame (not 
> generated by the kernel) and pass it to sigreturn, but this is presumably a 
> no-no anyway.

I see the point of saving/restore cs, but why ss and not es/ds ? 

-Andi