On 02/06/2012 12:32 AM, Indan Zupancic wrote: > > It seems that just using eflags is a lot simpler than the alternatives, > let's just go for it. > > > I propose using bits somewhere in the middle of the upper half. If new > flags are ever added by Intel or AMD, they will use the lower bits. If > anyone else ever adds flags, they most likely add them to the top (VIA). > So the middle seems the safest spot as far as long-term maintenance goes. > > The below version does that, but instead of setting one of the two bits, > it always sets bit 50 for newer kernels and sets bit 51 if it's a compat > system call. I find this version more readable and after compilation it's > also a couple of bytes smaller compared to Linus' original version. > > Should we make sure that the top 32 bits are zero, in case any weird > hardware does set our bits? > [Adding H.J. Lu, since he has run into some of these requirements before] NAK in the extreme. We have not heard back from the architecture people on this, and I will NAK this unless that happens. Furthermore, you're picking bits that do not work for 32 bits, EVEN THOUGH WE HAVE A SIMILAR PROBLEM ON 32 BITS; I outlined it for you and you chose to ignore it. Finally, I think we actually are going to need a fair number of bits in the end. All of this points to using a new regset designed for extension in the first place. As far as I can tell, we need at least the following information: - If the CPU is currently in 32- or 64-bit mode. - If we are currently inside a system call, and if so if it was entered via: - SYSCALL64 - INT 80 - SYSCALL32 - SYSENTER The reason we need this information is because for the various 32-bit entry points we do some very ugly swizzling of registers, which matters to a ptrace client which wants to modify system call arguments. - If the process was started as a 64-bit process, i386 process or x32 process. This adds up to a minimum of six bits already (and at least two bits on i386), and that's just a start. -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
