On Fri, Jan 13, 2012 at 11:31 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote: > On 01/12, Will Drewry wrote: >> >> On Thu, Jan 12, 2012 at 11:23 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote: >> > On 01/12, Will Drewry wrote: >> >> >> >> On Thu, Jan 12, 2012 at 10:22 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote: >> >> >> + */ >> >> >> + regs = seccomp_get_regs(regs_tmp, ®s_size); >> >> > >> >> > Stupid question. I am sure you know what are you doing ;) and I know >> >> > nothing about !x86 arches. >> >> > >> >> > But could you explain why it is designed to use user_regs_struct ? >> >> > Why we can't simply use task_pt_regs() and avoid the (costly) regsets? >> >> >> >> So on x86 32, it would work since user_regs_struct == task_pt_regs >> >> (iirc), but on x86-64 >> >> and others, that's not true. >> > >> > Yes sure, I meant that userpace should use pt_regs too. >> > >> >> If it would be appropriate to expose pt_regs to userspace, then I'd >> >> happily do so :) >> > >> > Ah, so that was the reason. But it is already exported? At least I see >> > the "#ifndef __KERNEL__" definition in arch/x86/include/asm/ptrace.h. >> > >> > Once again, I am not arguing, just trying to understand. And I do not >> > know if this definition is part of abi. >> >> I don't either :/ My original idea was to operate on task_pt_regs(current), >> but I noticed that PTRACE_GETREGS/SETREGS only uses the >> user_regs_struct. So I went that route. > > Well, I don't know where user_regs_struct come from initially. But > probably it is needed to allow to access the "artificial" things like > fs_base. Or perhaps this struct mimics the layout in the coredump. Not sure - added Roland whose name was on many of the files :) I just noticed that ptrace ABI allows pt_regs access using the register macros (PTRACE_PEEKUSR) and user_regs_struct access (PTRACE_GETREGS). But I think the latter is guaranteed to have a certain layout while the macros for PEEKUSR can do post-processing fixup. (Which could be done in the bpf evaluator load_pointer() helper if needed.) >> I'd love for pt_regs to be fair game to cut down on the copying! > > Me too. I see no point in using user_regs_struct. I'll rev the change to use pt_regs and drop all the helper code. If no one says otherwise, that certainly seems ideal from a performance perspective, and I see pt_regs exported to userland along with ptrace abi register offset macros. Thanks! will -- 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
