arch/powerpc/kernel/signal.c - linux - Git at Google

 /*
  * Common signal handling code for both 32 and 64 bits
  *
  *    Copyright (c) 2007 Benjamin Herrenschmidt, IBM Corporation
  *    Extracted from signal_32.c and signal_64.c
  *
  * This file is subject to the terms and conditions of the GNU General
  * Public License.  See the file README.legal in the main directory of
  * this archive for more details.
  */

 #include <linux/tracehook.h>
 #include <linux/signal.h>
 #include <linux/uprobes.h>
 #include <linux/key.h>
 #include <linux/context_tracking.h>
 #include <linux/livepatch.h>
 #include <linux/syscalls.h>
 #include <asm/hw_breakpoint.h>
 #include <linux/uaccess.h>
 #include <asm/switch_to.h>
 #include <asm/unistd.h>
 #include <asm/debug.h>
 #include <asm/tm.h>

 #include "signal.h"

 #ifdef CONFIG_VSX
 unsigned long copy_fpr_to_user(void __user *to,
 			       struct task_struct *task)
 {
 	u64 buf[ELF_NFPREG];
 	int i;

 	/* save FPR copy to local buffer then write to the thread_struct */
 	for (i = 0; i < (ELF_NFPREG - 1) ; i++)
 		buf[i] = task->thread.TS_FPR(i);
 	buf[i] = task->thread.fp_state.fpscr;
 	return __copy_to_user(to, buf, ELF_NFPREG * sizeof(double));
 }

 unsigned long copy_fpr_from_user(struct task_struct *task,
 				 void __user *from)
 {
 	u64 buf[ELF_NFPREG];
 	int i;

 	if (__copy_from_user(buf, from, ELF_NFPREG * sizeof(double)))
 		return 1;
 	for (i = 0; i < (ELF_NFPREG - 1) ; i++)
 		task->thread.TS_FPR(i) = buf[i];
 	task->thread.fp_state.fpscr = buf[i];

 	return 0;
 }

 unsigned long copy_vsx_to_user(void __user *to,
 			       struct task_struct *task)
 {
 	u64 buf[ELF_NVSRHALFREG];
 	int i;

 	/* save FPR copy to local buffer then write to the thread_struct */
 	for (i = 0; i < ELF_NVSRHALFREG; i++)
 		buf[i] = task->thread.fp_state.fpr[i][TS_VSRLOWOFFSET];
 	return __copy_to_user(to, buf, ELF_NVSRHALFREG * sizeof(double));
 }

 unsigned long copy_vsx_from_user(struct task_struct *task,
 				 void __user *from)
 {
 	u64 buf[ELF_NVSRHALFREG];
 	int i;

 	if (__copy_from_user(buf, from, ELF_NVSRHALFREG * sizeof(double)))
 		return 1;
 	for (i = 0; i < ELF_NVSRHALFREG ; i++)
 		task->thread.fp_state.fpr[i][TS_VSRLOWOFFSET] = buf[i];
 	return 0;
 }

 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
 unsigned long copy_ckfpr_to_user(void __user *to,
 				  struct task_struct *task)
 {
 	u64 buf[ELF_NFPREG];
 	int i;

 	/* save FPR copy to local buffer then write to the thread_struct */
 	for (i = 0; i < (ELF_NFPREG - 1) ; i++)
 		buf[i] = task->thread.TS_CKFPR(i);
 	buf[i] = task->thread.ckfp_state.fpscr;
 	return __copy_to_user(to, buf, ELF_NFPREG * sizeof(double));
 }

 unsigned long copy_ckfpr_from_user(struct task_struct *task,
 					  void __user *from)
 {
 	u64 buf[ELF_NFPREG];
 	int i;

 	if (__copy_from_user(buf, from, ELF_NFPREG * sizeof(double)))
 		return 1;
 	for (i = 0; i < (ELF_NFPREG - 1) ; i++)
 		task->thread.TS_CKFPR(i) = buf[i];
 	task->thread.ckfp_state.fpscr = buf[i];

 	return 0;
 }

 unsigned long copy_ckvsx_to_user(void __user *to,
 				  struct task_struct *task)
 {
 	u64 buf[ELF_NVSRHALFREG];
 	int i;

 	/* save FPR copy to local buffer then write to the thread_struct */
 	for (i = 0; i < ELF_NVSRHALFREG; i++)
 		buf[i] = task->thread.ckfp_state.fpr[i][TS_VSRLOWOFFSET];
 	return __copy_to_user(to, buf, ELF_NVSRHALFREG * sizeof(double));
 }

 unsigned long copy_ckvsx_from_user(struct task_struct *task,
 					  void __user *from)
 {
 	u64 buf[ELF_NVSRHALFREG];
 	int i;

 	if (__copy_from_user(buf, from, ELF_NVSRHALFREG * sizeof(double)))
 		return 1;
 	for (i = 0; i < ELF_NVSRHALFREG ; i++)
 		task->thread.ckfp_state.fpr[i][TS_VSRLOWOFFSET] = buf[i];
 	return 0;
 }
 #endif /* CONFIG_PPC_TRANSACTIONAL_MEM */
 #else
 inline unsigned long copy_fpr_to_user(void __user *to,
 				      struct task_struct *task)
 {
 	return __copy_to_user(to, task->thread.fp_state.fpr,
 			      ELF_NFPREG * sizeof(double));
 }

 inline unsigned long copy_fpr_from_user(struct task_struct *task,
 					void __user *from)
 {
 	return __copy_from_user(task->thread.fp_state.fpr, from,
 			      ELF_NFPREG * sizeof(double));
 }

 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
 inline unsigned long copy_ckfpr_to_user(void __user *to,
 					 struct task_struct *task)
 {
 	return __copy_to_user(to, task->thread.ckfp_state.fpr,
 			      ELF_NFPREG * sizeof(double));
 }

 inline unsigned long copy_ckfpr_from_user(struct task_struct *task,
 						 void __user *from)
 {
 	return __copy_from_user(task->thread.ckfp_state.fpr, from,
 				ELF_NFPREG * sizeof(double));
 }
 #endif /* CONFIG_PPC_TRANSACTIONAL_MEM */
 #endif

 /* Log an error when sending an unhandled signal to a process. Controlled
  * through debug.exception-trace sysctl.
  */

 int show_unhandled_signals = 1;

 /*
  * Allocate space for the signal frame
  */
 void __user *get_sigframe(struct ksignal *ksig, unsigned long sp,
 			   size_t frame_size, int is_32)
 {
         unsigned long oldsp, newsp;

         /* Default to using normal stack */
         oldsp = get_clean_sp(sp, is_32);
 	oldsp = sigsp(oldsp, ksig);
 	newsp = (oldsp - frame_size) & ~0xFUL;

 	/* Check access */
 	if (!access_ok((void __user *)newsp, oldsp - newsp))
 		return NULL;

         return (void __user *)newsp;
 }

 static void check_syscall_restart(struct pt_regs *regs, struct k_sigaction *ka,
 				  int has_handler)
 {
 	unsigned long ret = regs->gpr[3];
 	int restart = 1;

 	/* syscall ? */
 	if (!trap_is_syscall(regs))
 		return;

 	if (trap_norestart(regs))
 		return;

 	/* error signalled ? */
 	if (trap_is_scv(regs)) {
 		/* 32-bit compat mode sign extend? */
 		if (!IS_ERR_VALUE(ret))
 			return;
 		ret = -ret;
 	} else if (!(regs->ccr & 0x10000000)) {
 		return;
 	}

 	switch (ret) {
 	case ERESTART_RESTARTBLOCK:
 	case ERESTARTNOHAND:
 		/* ERESTARTNOHAND means that the syscall should only be
 		 * restarted if there was no handler for the signal, and since
 		 * we only get here if there is a handler, we dont restart.
 		 */
 		restart = !has_handler;
 		break;
 	case ERESTARTSYS:
 		/* ERESTARTSYS means to restart the syscall if there is no
 		 * handler or the handler was registered with SA_RESTART
 		 */
 		restart = !has_handler || (ka->sa.sa_flags & SA_RESTART) != 0;
 		break;
 	case ERESTARTNOINTR:
 		/* ERESTARTNOINTR means that the syscall should be
 		 * called again after the signal handler returns.
 		 */
 		break;
 	default:
 		return;
 	}
 	if (restart) {
 		if (ret == ERESTART_RESTARTBLOCK)
 			regs->gpr[0] = __NR_restart_syscall;
 		else
 			regs->gpr[3] = regs->orig_gpr3;
 		regs->nip -= 4;
 		regs->result = 0;
 	} else {
 		if (trap_is_scv(regs)) {
 			regs->result = -EINTR;
 			regs->gpr[3] = -EINTR;
 		} else {
 			regs->result = -EINTR;
 			regs->gpr[3] = EINTR;
 			regs->ccr |= 0x10000000;
 		}
 	}
 }

 static void do_signal(struct task_struct *tsk)
 {
 	sigset_t *oldset = sigmask_to_save();
 	struct ksignal ksig = { .sig = 0 };
 	int ret;

 	BUG_ON(tsk != current);

 	get_signal(&ksig);

 	/* Is there any syscall restart business here ? */
 	check_syscall_restart(tsk->thread.regs, &ksig.ka, ksig.sig > 0);

 	if (ksig.sig <= 0) {
 		/* No signal to deliver -- put the saved sigmask back */
 		restore_saved_sigmask();
 		set_trap_norestart(tsk->thread.regs);
 		return;               /* no signals delivered */
 	}

         /*
 	 * Reenable the DABR before delivering the signal to
 	 * user space. The DABR will have been cleared if it
 	 * triggered inside the kernel.
 	 */
 	if (!IS_ENABLED(CONFIG_PPC_ADV_DEBUG_REGS)) {
 		int i;

 		for (i = 0; i < nr_wp_slots(); i++) {
 			if (tsk->thread.hw_brk[i].address && tsk->thread.hw_brk[i].type)
 				__set_breakpoint(i, &tsk->thread.hw_brk[i]);
 		}
 	}

 	/* Re-enable the breakpoints for the signal stack */
 	thread_change_pc(tsk, tsk->thread.regs);

 	rseq_signal_deliver(&ksig, tsk->thread.regs);

 	if (is_32bit_task()) {
         	if (ksig.ka.sa.sa_flags & SA_SIGINFO)
 			ret = handle_rt_signal32(&ksig, oldset, tsk);
 		else
 			ret = handle_signal32(&ksig, oldset, tsk);
 	} else {
 		ret = handle_rt_signal64(&ksig, oldset, tsk);
 	}

 	set_trap_norestart(tsk->thread.regs);
 	signal_setup_done(ret, &ksig, test_thread_flag(TIF_SINGLESTEP));
 }

 void do_notify_resume(struct pt_regs *regs, unsigned long thread_info_flags)
 {
 	user_exit();

 	/* Check valid addr_limit, TIF check is done there */
 	addr_limit_user_check();

 	if (thread_info_flags & _TIF_UPROBE)
 		uprobe_notify_resume(regs);

 	if (thread_info_flags & _TIF_PATCH_PENDING)
 		klp_update_patch_state(current);

 	if (thread_info_flags & _TIF_SIGPENDING) {
 		BUG_ON(regs != current->thread.regs);
 		do_signal(current);
 	}

 	if (thread_info_flags & _TIF_NOTIFY_RESUME) {
 		clear_thread_flag(TIF_NOTIFY_RESUME);
 		tracehook_notify_resume(regs);
 		rseq_handle_notify_resume(NULL, regs);
 	}

 	user_enter();
 }

 unsigned long get_tm_stackpointer(struct task_struct *tsk)
 {
 	/* When in an active transaction that takes a signal, we need to be
 	 * careful with the stack.  It's possible that the stack has moved back
 	 * up after the tbegin.  The obvious case here is when the tbegin is
 	 * called inside a function that returns before a tend.  In this case,
 	 * the stack is part of the checkpointed transactional memory state.
 	 * If we write over this non transactionally or in suspend, we are in
 	 * trouble because if we get a tm abort, the program counter and stack
 	 * pointer will be back at the tbegin but our in memory stack won't be
 	 * valid anymore.
 	 *
 	 * To avoid this, when taking a signal in an active transaction, we
 	 * need to use the stack pointer from the checkpointed state, rather
 	 * than the speculated state.  This ensures that the signal context
 	 * (written tm suspended) will be written below the stack required for
 	 * the rollback.  The transaction is aborted because of the treclaim,
 	 * so any memory written between the tbegin and the signal will be
 	 * rolled back anyway.
 	 *
 	 * For signals taken in non-TM or suspended mode, we use the
 	 * normal/non-checkpointed stack pointer.
 	 */

 	unsigned long ret = tsk->thread.regs->gpr[1];

 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
 	BUG_ON(tsk != current);

 	if (MSR_TM_ACTIVE(tsk->thread.regs->msr)) {
 		preempt_disable();
 		tm_reclaim_current(TM_CAUSE_SIGNAL);
 		if (MSR_TM_TRANSACTIONAL(tsk->thread.regs->msr))
 			ret = tsk->thread.ckpt_regs.gpr[1];

 		/*
 		 * If we treclaim, we must clear the current thread's TM bits
 		 * before re-enabling preemption. Otherwise we might be
 		 * preempted and have the live MSR[TS] changed behind our back
 		 * (tm_recheckpoint_new_task() would recheckpoint). Besides, we
 		 * enter the signal handler in non-transactional state.
 		 */
 		tsk->thread.regs->msr &= ~MSR_TS_MASK;
 		preempt_enable();
 	}
 #endif
 	return ret;
 }
	/*
	* Common signal handling code for both 32 and 64 bits
	*
	* Copyright (c) 2007 Benjamin Herrenschmidt, IBM Corporation
	* Extracted from signal_32.c and signal_64.c
	*
	* This file is subject to the terms and conditions of the GNU General
	* Public License. See the file README.legal in the main directory of
	* this archive for more details.
	*/

	#include <linux/tracehook.h>
	#include <linux/signal.h>
	#include <linux/uprobes.h>
	#include <linux/key.h>
	#include <linux/context_tracking.h>
	#include <linux/livepatch.h>
	#include <linux/syscalls.h>
	#include <asm/hw_breakpoint.h>
	#include <linux/uaccess.h>
	#include <asm/switch_to.h>
	#include <asm/unistd.h>
	#include <asm/debug.h>
	#include <asm/tm.h>

	#include "signal.h"

	#ifdef CONFIG_VSX
	unsigned long copy_fpr_to_user(void __user *to,
	struct task_struct *task)
	{
	u64 buf[ELF_NFPREG];
	int i;

	/* save FPR copy to local buffer then write to the thread_struct */
	for (i = 0; i < (ELF_NFPREG - 1) ; i++)
	buf[i] = task->thread.TS_FPR(i);
	buf[i] = task->thread.fp_state.fpscr;
	return __copy_to_user(to, buf, ELF_NFPREG * sizeof(double));
	}

	unsigned long copy_fpr_from_user(struct task_struct *task,
	void __user *from)
	{
	u64 buf[ELF_NFPREG];
	int i;

	if (__copy_from_user(buf, from, ELF_NFPREG * sizeof(double)))
	return 1;
	for (i = 0; i < (ELF_NFPREG - 1) ; i++)
	task->thread.TS_FPR(i) = buf[i];
	task->thread.fp_state.fpscr = buf[i];

	return 0;
	}

	unsigned long copy_vsx_to_user(void __user *to,
	struct task_struct *task)
	{
	u64 buf[ELF_NVSRHALFREG];
	int i;

	/* save FPR copy to local buffer then write to the thread_struct */
	for (i = 0; i < ELF_NVSRHALFREG; i++)
	buf[i] = task->thread.fp_state.fpr[i][TS_VSRLOWOFFSET];
	return __copy_to_user(to, buf, ELF_NVSRHALFREG * sizeof(double));
	}

	unsigned long copy_vsx_from_user(struct task_struct *task,
	void __user *from)
	{
	u64 buf[ELF_NVSRHALFREG];
	int i;

	if (__copy_from_user(buf, from, ELF_NVSRHALFREG * sizeof(double)))
	return 1;
	for (i = 0; i < ELF_NVSRHALFREG ; i++)
	task->thread.fp_state.fpr[i][TS_VSRLOWOFFSET] = buf[i];
	return 0;
	}

	#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
	unsigned long copy_ckfpr_to_user(void __user *to,
	struct task_struct *task)
	{
	u64 buf[ELF_NFPREG];
	int i;

	/* save FPR copy to local buffer then write to the thread_struct */
	for (i = 0; i < (ELF_NFPREG - 1) ; i++)
	buf[i] = task->thread.TS_CKFPR(i);
	buf[i] = task->thread.ckfp_state.fpscr;
	return __copy_to_user(to, buf, ELF_NFPREG * sizeof(double));
	}

	unsigned long copy_ckfpr_from_user(struct task_struct *task,
	void __user *from)
	{
	u64 buf[ELF_NFPREG];
	int i;

	if (__copy_from_user(buf, from, ELF_NFPREG * sizeof(double)))
	return 1;
	for (i = 0; i < (ELF_NFPREG - 1) ; i++)
	task->thread.TS_CKFPR(i) = buf[i];
	task->thread.ckfp_state.fpscr = buf[i];

	return 0;
	}

	unsigned long copy_ckvsx_to_user(void __user *to,
	struct task_struct *task)
	{
	u64 buf[ELF_NVSRHALFREG];
	int i;

	/* save FPR copy to local buffer then write to the thread_struct */
	for (i = 0; i < ELF_NVSRHALFREG; i++)
	buf[i] = task->thread.ckfp_state.fpr[i][TS_VSRLOWOFFSET];
	return __copy_to_user(to, buf, ELF_NVSRHALFREG * sizeof(double));
	}

	unsigned long copy_ckvsx_from_user(struct task_struct *task,
	void __user *from)
	{
	u64 buf[ELF_NVSRHALFREG];
	int i;

	if (__copy_from_user(buf, from, ELF_NVSRHALFREG * sizeof(double)))
	return 1;
	for (i = 0; i < ELF_NVSRHALFREG ; i++)
	task->thread.ckfp_state.fpr[i][TS_VSRLOWOFFSET] = buf[i];
	return 0;
	}
	#endif /* CONFIG_PPC_TRANSACTIONAL_MEM */
	#else
	inline unsigned long copy_fpr_to_user(void __user *to,
	struct task_struct *task)
	{
	return __copy_to_user(to, task->thread.fp_state.fpr,
	ELF_NFPREG * sizeof(double));
	}

	inline unsigned long copy_fpr_from_user(struct task_struct *task,
	void __user *from)
	{
	return __copy_from_user(task->thread.fp_state.fpr, from,
	ELF_NFPREG * sizeof(double));
	}

	#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
	inline unsigned long copy_ckfpr_to_user(void __user *to,
	struct task_struct *task)
	{
	return __copy_to_user(to, task->thread.ckfp_state.fpr,
	ELF_NFPREG * sizeof(double));
	}

	inline unsigned long copy_ckfpr_from_user(struct task_struct *task,
	void __user *from)
	{
	return __copy_from_user(task->thread.ckfp_state.fpr, from,
	ELF_NFPREG * sizeof(double));
	}
	#endif /* CONFIG_PPC_TRANSACTIONAL_MEM */
	#endif

	/* Log an error when sending an unhandled signal to a process. Controlled
	* through debug.exception-trace sysctl.
	*/

	int show_unhandled_signals = 1;

	/*
	* Allocate space for the signal frame
	*/
	void __user get_sigframe(struct ksignal ksig, unsigned long sp,
	size_t frame_size, int is_32)
	{
	unsigned long oldsp, newsp;

	/* Default to using normal stack */
	oldsp = get_clean_sp(sp, is_32);
	oldsp = sigsp(oldsp, ksig);
	newsp = (oldsp - frame_size) & ~0xFUL;

	/* Check access */
	if (!access_ok((void __user *)newsp, oldsp - newsp))
	return NULL;

	return (void __user *)newsp;
	}

	static void check_syscall_restart(struct pt_regs regs, struct k_sigaction ka,
	int has_handler)
	{
	unsigned long ret = regs->gpr[3];
	int restart = 1;

	/* syscall ? */
	if (!trap_is_syscall(regs))
	return;

	if (trap_norestart(regs))
	return;

	/* error signalled ? */
	if (trap_is_scv(regs)) {
	/* 32-bit compat mode sign extend? */
	if (!IS_ERR_VALUE(ret))
	return;
	ret = -ret;
	} else if (!(regs->ccr & 0x10000000)) {
	return;
	}

	switch (ret) {
	case ERESTART_RESTARTBLOCK:
	case ERESTARTNOHAND:
	/* ERESTARTNOHAND means that the syscall should only be
	* restarted if there was no handler for the signal, and since
	* we only get here if there is a handler, we dont restart.
	*/
	restart = !has_handler;
	break;
	case ERESTARTSYS:
	/* ERESTARTSYS means to restart the syscall if there is no
	* handler or the handler was registered with SA_RESTART
	*/
	restart = !has_handler \|\| (ka->sa.sa_flags & SA_RESTART) != 0;
	break;
	case ERESTARTNOINTR:
	/* ERESTARTNOINTR means that the syscall should be
	* called again after the signal handler returns.
	*/
	break;
	default:
	return;
	}
	if (restart) {
	if (ret == ERESTART_RESTARTBLOCK)
	regs->gpr[0] = __NR_restart_syscall;
	else
	regs->gpr[3] = regs->orig_gpr3;
	regs->nip -= 4;
	regs->result = 0;
	} else {
	if (trap_is_scv(regs)) {
	regs->result = -EINTR;
	regs->gpr[3] = -EINTR;
	} else {
	regs->result = -EINTR;
	regs->gpr[3] = EINTR;
	regs->ccr \|= 0x10000000;
	}
	}
	}

	static void do_signal(struct task_struct *tsk)
	{
	sigset_t *oldset = sigmask_to_save();
	struct ksignal ksig = { .sig = 0 };
	int ret;

	BUG_ON(tsk != current);

	get_signal(&ksig);

	/* Is there any syscall restart business here ? */
	check_syscall_restart(tsk->thread.regs, &ksig.ka, ksig.sig > 0);

	if (ksig.sig <= 0) {
	/* No signal to deliver -- put the saved sigmask back */
	restore_saved_sigmask();
	set_trap_norestart(tsk->thread.regs);
	return; /* no signals delivered */
	}

	/*
	* Reenable the DABR before delivering the signal to
	* user space. The DABR will have been cleared if it
	* triggered inside the kernel.
	*/
	if (!IS_ENABLED(CONFIG_PPC_ADV_DEBUG_REGS)) {
	int i;

	for (i = 0; i < nr_wp_slots(); i++) {
	if (tsk->thread.hw_brk[i].address && tsk->thread.hw_brk[i].type)
	__set_breakpoint(i, &tsk->thread.hw_brk[i]);
	}
	}

	/* Re-enable the breakpoints for the signal stack */
	thread_change_pc(tsk, tsk->thread.regs);

	rseq_signal_deliver(&ksig, tsk->thread.regs);

	if (is_32bit_task()) {
	if (ksig.ka.sa.sa_flags & SA_SIGINFO)
	ret = handle_rt_signal32(&ksig, oldset, tsk);
	else
	ret = handle_signal32(&ksig, oldset, tsk);
	} else {
	ret = handle_rt_signal64(&ksig, oldset, tsk);
	}

	set_trap_norestart(tsk->thread.regs);
	signal_setup_done(ret, &ksig, test_thread_flag(TIF_SINGLESTEP));
	}

	void do_notify_resume(struct pt_regs *regs, unsigned long thread_info_flags)
	{
	user_exit();

	/* Check valid addr_limit, TIF check is done there */
	addr_limit_user_check();

	if (thread_info_flags & _TIF_UPROBE)
	uprobe_notify_resume(regs);

	if (thread_info_flags & _TIF_PATCH_PENDING)
	klp_update_patch_state(current);

	if (thread_info_flags & _TIF_SIGPENDING) {
	BUG_ON(regs != current->thread.regs);
	do_signal(current);
	}

	if (thread_info_flags & _TIF_NOTIFY_RESUME) {
	clear_thread_flag(TIF_NOTIFY_RESUME);
	tracehook_notify_resume(regs);
	rseq_handle_notify_resume(NULL, regs);
	}

	user_enter();
	}

	unsigned long get_tm_stackpointer(struct task_struct *tsk)
	{
	/* When in an active transaction that takes a signal, we need to be
	* careful with the stack. It's possible that the stack has moved back
	* up after the tbegin. The obvious case here is when the tbegin is
	* called inside a function that returns before a tend. In this case,
	* the stack is part of the checkpointed transactional memory state.
	* If we write over this non transactionally or in suspend, we are in
	* trouble because if we get a tm abort, the program counter and stack
	* pointer will be back at the tbegin but our in memory stack won't be
	* valid anymore.
	*
	* To avoid this, when taking a signal in an active transaction, we
	* need to use the stack pointer from the checkpointed state, rather
	* than the speculated state. This ensures that the signal context
	* (written tm suspended) will be written below the stack required for
	* the rollback. The transaction is aborted because of the treclaim,
	* so any memory written between the tbegin and the signal will be
	* rolled back anyway.
	*
	* For signals taken in non-TM or suspended mode, we use the
	* normal/non-checkpointed stack pointer.
	*/

	unsigned long ret = tsk->thread.regs->gpr[1];

	#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
	BUG_ON(tsk != current);

	if (MSR_TM_ACTIVE(tsk->thread.regs->msr)) {
	preempt_disable();
	tm_reclaim_current(TM_CAUSE_SIGNAL);
	if (MSR_TM_TRANSACTIONAL(tsk->thread.regs->msr))
	ret = tsk->thread.ckpt_regs.gpr[1];

	/*
	* If we treclaim, we must clear the current thread's TM bits
	* before re-enabling preemption. Otherwise we might be
	* preempted and have the live MSR[TS] changed behind our back
	* (tm_recheckpoint_new_task() would recheckpoint). Besides, we
	* enter the signal handler in non-transactional state.
	*/
	tsk->thread.regs->msr &= ~MSR_TS_MASK;
	preempt_enable();
	}
	#endif
	return ret;
	}