perf/x86_64: Improve user regs sampling

			struct pt_regs *regs,

			struct pt_regs *regs_user_copy)

{

	regs_user->regs = task_pt_regs(current);

	regs_user->abi = perf_reg_abi(current);

	struct pt_regs *user_regs = task_pt_regs(current);

	/*

	 * If we're in an NMI that interrupted task_pt_regs setup, then

	 * we can't sample user regs at all.  This check isn't really

	 * sufficient, though, as we could be in an NMI inside an interrupt

	 * that happened during task_pt_regs setup.

	 */

	if (regs->sp > (unsigned long)&user_regs->r11 &&

	    regs->sp <= (unsigned long)(user_regs + 1)) {

		regs_user->abi = PERF_SAMPLE_REGS_ABI_NONE;

		regs_user->regs = NULL;

		return;

	}

	/*

	 * RIP, flags, and the argument registers are usually saved.

	 * orig_ax is probably okay, too.

	 */

	regs_user_copy->ip = user_regs->ip;

	regs_user_copy->cx = user_regs->cx;

	regs_user_copy->dx = user_regs->dx;

	regs_user_copy->si = user_regs->si;

	regs_user_copy->di = user_regs->di;

	regs_user_copy->r8 = user_regs->r8;

	regs_user_copy->r9 = user_regs->r9;

	regs_user_copy->r10 = user_regs->r10;

	regs_user_copy->r11 = user_regs->r11;

	regs_user_copy->orig_ax = user_regs->orig_ax;

	regs_user_copy->flags = user_regs->flags;

	/*

	 * Don't even try to report the "rest" regs.

	 */

	regs_user_copy->bx = -1;

	regs_user_copy->bp = -1;

	regs_user_copy->r12 = -1;

	regs_user_copy->r13 = -1;

	regs_user_copy->r14 = -1;

	regs_user_copy->r15 = -1;

	/*

	 * For this to be at all useful, we need a reasonable guess for

	 * sp and the ABI.  Be careful: we're in NMI context, and we're

	 * considering current to be the current task, so we should

	 * be careful not to look at any other percpu variables that might

	 * change during context switches.

	 */

	if (IS_ENABLED(CONFIG_IA32_EMULATION) &&

	    task_thread_info(current)->status & TS_COMPAT) {

		/* Easy case: we're in a compat syscall. */

		regs_user->abi = PERF_SAMPLE_REGS_ABI_32;

		regs_user_copy->sp = user_regs->sp;

		regs_user_copy->cs = user_regs->cs;

		regs_user_copy->ss = user_regs->ss;

	} else if (user_regs->orig_ax != -1) {

		/*

		 * We're probably in a 64-bit syscall.

		 * Warning: this code is severely racy.  At least it's better

		 * than just blindly copying user_regs.

		 */

		regs_user->abi = PERF_SAMPLE_REGS_ABI_64;

		regs_user_copy->sp = this_cpu_read(old_rsp);

		regs_user_copy->cs = __USER_CS;

		regs_user_copy->ss = __USER_DS;

		regs_user_copy->cx = -1;  /* usually contains garbage */

	} else {

		/* We're probably in an interrupt or exception. */

		regs_user->abi = user_64bit_mode(user_regs) ?

			PERF_SAMPLE_REGS_ABI_64 : PERF_SAMPLE_REGS_ABI_32;

		regs_user_copy->sp = user_regs->sp;

		regs_user_copy->cs = user_regs->cs;

		regs_user_copy->ss = user_regs->ss;

	}

	regs_user->regs = regs_user_copy;

}

#endif /* CONFIG_X86_32 */