csky: Reconstruct signal processing

Linux kernel has provided some apis for arch signal's implementation.
For example:
	restore_saved_sigmask()
	set_current_blocked()
	restore_altstack()

But in last version of csky signal.c didn't use them and some codes are
confusing, so reconstruct signal.c with reference to riscv's code.

Now csky signal.c implementation are very close to riscv and we can
get the following benefits:
 - Clear code structure
 - The signal code of riscv and csky can be reviewed together
 - Promoting the unification of arch's signal implementation

Also modified the related code in entry.S

Signed-off-by: Guo Ren <ren_guo@c-sky.com>
Cc: Arnd Bergmann <arnd@arndb.de>

3 files changed, 146 insertions, 260 deletions

diff --git a/arch/csky/kernel/atomic.S b/arch/csky/kernel/atomic.S
index d2357c8f85bd..5b84f11485ae 100644
--- a/arch/csky/kernel/atomic.S
+++ b/arch/csky/kernel/atomic.S
@@ -12,11 +12,10 @@
  * If *ptr != oldval && return 1,
  * else *ptr = newval return 0.
  */
-#ifdef CONFIG_CPU_HAS_LDSTEX
 ENTRY(csky_cmpxchg)
 	USPTOKSP
 	mfcr	a3, epc
-	INCTRAP	a3
+	addi	a3, TRAP0_SIZE
 
 	subi    sp, 8
 	stw     a3, (sp, 0)
@@ -24,6 +23,7 @@ ENTRY(csky_cmpxchg)
 	stw     a3, (sp, 4)
 
 	psrset	ee
+#ifdef CONFIG_CPU_HAS_LDSTEX
 1:
 	ldex	a3, (a2)
 	cmpne	a0, a3
@@ -33,27 +33,7 @@ ENTRY(csky_cmpxchg)
 	bez	a3, 1b
 2:
 	sync.is
-	mvc	a0
-	ldw	a3, (sp, 0)
-	mtcr	a3, epc
-	ldw     a3, (sp, 4)
-	mtcr	a3, epsr
-	addi	sp, 8
-	KSPTOUSP
-	rte
-END(csky_cmpxchg)
 #else
-ENTRY(csky_cmpxchg)
-	USPTOKSP
-	mfcr	a3, epc
-	INCTRAP	a3
-
-	subi    sp, 8
-	stw     a3, (sp, 0)
-	mfcr    a3, epsr
-	stw     a3, (sp, 4)
-
-	psrset	ee
 1:
 	ldw	a3, (a2)
 	cmpne	a0, a3
@@ -61,6 +41,7 @@ ENTRY(csky_cmpxchg)
 2:
 	stw	a1, (a2)
 3:
+#endif
 	mvc	a0
 	ldw	a3, (sp, 0)
 	mtcr	a3, epc
@@ -71,6 +52,7 @@ ENTRY(csky_cmpxchg)
 	rte
 END(csky_cmpxchg)
 
+#ifndef CONFIG_CPU_HAS_LDSTEX
 /*
  * Called from tlbmodified exception
  */
diff --git a/arch/csky/kernel/entry.S b/arch/csky/kernel/entry.S
index b3b3b0bbfcc7..c0f80736dac6 100644
--- a/arch/csky/kernel/entry.S
+++ b/arch/csky/kernel/entry.S
@@ -91,7 +91,7 @@ ENTRY(csky_\name)
 	mfcr    a3, ss2
 	mfcr    r6, ss3
 	mfcr    a2, ss4
-	SAVE_ALL EPC_KEEP
+	SAVE_ALL 0
 .endm
 .macro tlbop_end is_write
 	RD_MEH	a2
@@ -117,7 +117,7 @@ jbsr csky_cmpxchg_fixup
 tlbop_end 1
 
 ENTRY(csky_systemcall)
-	SAVE_ALL EPC_INCREASE
+	SAVE_ALL TRAP0_SIZE
 
 	psrset  ee, ie
 
@@ -190,11 +190,9 @@ ENTRY(ret_from_fork)
 	ldw	r8, (r9, TINFO_FLAGS)
 	ANDI_R3	r8, (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_TRACEPOINT | _TIF_SYSCALL_AUDIT)
 	cmpnei	r8, 0
-	bf	3f
+	bf	ret_from_exception
 	mov	a0, sp			/* sp = pt_regs pointer */
 	jbsr	syscall_trace_exit
-3:
-	jbsr	ret_from_exception
 
 ret_from_exception:
 	ld	syscallid, (sp, LSAVE_PSR)
@@ -209,34 +207,29 @@ ret_from_exception:
 	bmaski	r10, THREAD_SHIFT
 	andn	r9, r10
 
-resume_userspace:
 	ldw	r8, (r9, TINFO_FLAGS)
 	andi	r8, (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_NEED_RESCHED)
 	cmpnei	r8, 0
 	bt	exit_work
-1:  RESTORE_ALL
+1:
+	RESTORE_ALL
 
 exit_work:
+	lrw	syscallid, ret_from_exception
+	mov	lr, syscallid
+
 	btsti	r8, TIF_NEED_RESCHED
 	bt	work_resched
-	/* If thread_info->flag is empty, RESTORE_ALL */
-	cmpnei	r8, 0
-	bf	1b
-	mov	a0, r8
-	mov	a1, sp
-	jbsr	do_notify_resume	/* do signals */
-	br	resume_userspace
+
+	mov	a0, sp
+	mov	a1, r8
+	jmpi	do_notify_resume
 
 work_resched:
-	lrw	syscallid, ret_from_exception
-	mov	r15, syscallid		/* Return address in link */
 	jmpi	schedule
 
-ENTRY(sys_rt_sigreturn)
-	jmpi	do_rt_sigreturn
-
 ENTRY(csky_trap)
-	SAVE_ALL EPC_KEEP
+	SAVE_ALL 0
 	psrset	ee
 	mov	a0, sp                 /* Push Stack pointer arg */
 	jbsr	trap_c                 /* Call C-level trap handler */
@@ -252,7 +245,7 @@ ENTRY(csky_get_tls)
 
 	/* increase epc for continue */
 	mfcr	a0, epc
-	INCTRAP	a0
+	addi	a0, TRAP0_SIZE
 	mtcr	a0, epc
 
 	/* get current task thread_info with kernel 8K stack */
@@ -269,7 +262,7 @@ ENTRY(csky_get_tls)
 	rte
 
 ENTRY(csky_irq)
-	SAVE_ALL EPC_KEEP
+	SAVE_ALL 0
 	psrset	ee
 
 #ifdef CONFIG_PREEMPT
diff --git a/arch/csky/kernel/signal.c b/arch/csky/kernel/signal.c
index 5a18940f0b09..04a43cfd4e09 100644
--- a/arch/csky/kernel/signal.c
+++ b/arch/csky/kernel/signal.c
@@ -1,26 +1,10 @@
 // SPDX-License-Identifier: GPL-2.0
-// Copyright (C) 2018 Hangzhou C-SKY Microsystems co.,ltd.
 
-#include <linux/sched.h>
-#include <linux/mm.h>
-#include <linux/kernel.h>
 #include <linux/signal.h>
+#include <linux/uaccess.h>
 #include <linux/syscalls.h>
-#include <linux/errno.h>
-#include <linux/wait.h>
-#include <linux/ptrace.h>
-#include <linux/unistd.h>
-#include <linux/stddef.h>
-#include <linux/highuid.h>
-#include <linux/personality.h>
-#include <linux/tty.h>
-#include <linux/binfmts.h>
 #include <linux/tracehook.h>
-#include <linux/freezer.h>
-#include <linux/uaccess.h>
 
-#include <asm/setup.h>
-#include <asm/pgtable.h>
 #include <asm/traps.h>
 #include <asm/ucontext.h>
 #include <asm/vdso.h>
@@ -29,110 +13,117 @@
 
 #ifdef CONFIG_CPU_HAS_FPU
 #include <abi/fpu.h>
-
-static int restore_fpu_state(struct sigcontext *sc)
+static int restore_fpu_state(struct sigcontext __user *sc)
 {
 	int err = 0;
 	struct user_fp user_fp;
 
-	err = copy_from_user(&user_fp, &sc->sc_user_fp, sizeof(user_fp));
+	err = __copy_from_user(&user_fp, &sc->sc_user_fp, sizeof(user_fp));
 
 	restore_from_user_fp(&user_fp);
 
 	return err;
 }
 
-static int save_fpu_state(struct sigcontext *sc)
+static int save_fpu_state(struct sigcontext __user *sc)
 {
 	struct user_fp user_fp;
 
 	save_to_user_fp(&user_fp);
 
-	return copy_to_user(&sc->sc_user_fp, &user_fp, sizeof(user_fp));
+	return __copy_to_user(&sc->sc_user_fp, &user_fp, sizeof(user_fp));
 }
 #else
-static inline int restore_fpu_state(struct sigcontext *sc) { return 0; }
-static inline int save_fpu_state(struct sigcontext *sc) { return 0; }
+#define restore_fpu_state(sigcontext)	(0)
+#define save_fpu_state(sigcontext)	(0)
 #endif
 
 struct rt_sigframe {
-	int sig;
-	struct siginfo *pinfo;
-	void *puc;
 	struct siginfo info;
 	struct ucontext uc;
 };
 
-static int
-restore_sigframe(struct pt_regs *regs,
-		 struct sigcontext *sc, int *pr2)
+static long restore_sigcontext(struct pt_regs *regs,
+	struct sigcontext __user *sc)
 {
 	int err = 0;
 
-	/* Always make any pending restarted system calls return -EINTR */
-	current_thread_info()->task->restart_block.fn = do_no_restart_syscall;
-
-	err |= copy_from_user(regs, &sc->sc_pt_regs, sizeof(struct pt_regs));
+	/* sc_pt_regs is structured the same as the start of pt_regs */
+	err |= __copy_from_user(regs, &sc->sc_pt_regs, sizeof(struct pt_regs));
 
+	/* Restore the floating-point state. */
 	err |= restore_fpu_state(sc);
 
-	*pr2 = regs->a0;
 	return err;
 }
 
-asmlinkage int
-do_rt_sigreturn(void)
+SYSCALL_DEFINE0(rt_sigreturn)
 {
-	sigset_t set;
-	int a0;
 	struct pt_regs *regs = current_pt_regs();
-	struct rt_sigframe *frame = (struct rt_sigframe *)(regs->usp);
+	struct rt_sigframe __user *frame;
+	struct task_struct *task;
+	sigset_t set;
+
+	/* Always make any pending restarted system calls return -EINTR */
+	current->restart_block.fn = do_no_restart_syscall;
+
+	frame = (struct rt_sigframe __user *)regs->usp;
 
 	if (!access_ok(frame, sizeof(*frame)))
 		goto badframe;
+
 	if (__copy_from_user(&set, &frame->uc.uc_sigmask, sizeof(set)))
 		goto badframe;
 
-	sigdelsetmask(&set, (sigmask(SIGKILL) | sigmask(SIGSTOP)));
-	spin_lock_irq(&current->sighand->siglock);
-	current->blocked = set;
-	recalc_sigpending();
-	spin_unlock_irq(&current->sighand->siglock);
+	set_current_blocked(&set);
+
+	if (restore_sigcontext(regs, &frame->uc.uc_mcontext))
+		goto badframe;
 
-	if (restore_sigframe(regs, &frame->uc.uc_mcontext, &a0))
+	if (restore_altstack(&frame->uc.uc_stack))
 		goto badframe;
 
-	return a0;
+	return regs->a0;
 
 badframe:
-	force_sig(SIGSEGV, current);
+	task = current;
+	force_sig(SIGSEGV, task);
 	return 0;
 }
 
-static int setup_sigframe(struct sigcontext *sc, struct pt_regs *regs)
+static int setup_sigcontext(struct rt_sigframe __user *frame,
+	struct pt_regs *regs)
 {
+	struct sigcontext __user *sc = &frame->uc.uc_mcontext;
 	int err = 0;
 
-	err |= copy_to_user(&sc->sc_pt_regs, regs, sizeof(struct pt_regs));
+	err |= __copy_to_user(&sc->sc_pt_regs, regs, sizeof(struct pt_regs));
 	err |= save_fpu_state(sc);
 
 	return err;
 }
 
-static inline void *
-get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, size_t frame_size)
+static inline void __user *get_sigframe(struct ksignal *ksig,
+	struct pt_regs *regs, size_t framesize)
 {
-	unsigned long usp;
+	unsigned long sp;
+	/* Default to using normal stack */
+	sp = regs->usp;
 
-	/* Default to using normal stack.  */
-	usp = regs->usp;
+	/*
+	 * If we are on the alternate signal stack and would overflow it, don't.
+	 * Return an always-bogus address instead so we will die with SIGSEGV.
+	 */
+	if (on_sig_stack(sp) && !likely(on_sig_stack(sp - framesize)))
+		return (void __user __force *)(-1UL);
 
-	/* This is the X/Open sanctioned signal stack switching.  */
-	if ((ka->sa.sa_flags & SA_ONSTACK) && !sas_ss_flags(usp)) {
-		if (!on_sig_stack(usp))
-			usp = current->sas_ss_sp + current->sas_ss_size;
-	}
-	return (void *)((usp - frame_size) & -8UL);
+	/* This is the X/Open sanctioned signal stack switching. */
+	sp = sigsp(sp, ksig) - framesize;
+
+	/* Align the stack frame. */
+	sp &= -8UL;
+
+	return (void __user *)sp;
 }
 
 static int
@@ -140,208 +131,128 @@ setup_rt_frame(struct ksignal *ksig, sigset_t *set, struct pt_regs *regs)
 {
 	struct rt_sigframe *frame;
 	int err = 0;
-
 	struct csky_vdso *vdso = current->mm->context.vdso;
 
-	frame = get_sigframe(&ksig->ka, regs, sizeof(*frame));
-	if (!frame)
-		return 1;
+	frame = get_sigframe(ksig, regs, sizeof(*frame));
+	if (!access_ok(frame, sizeof(*frame)))
+		return -EFAULT;
 
-	err |= __put_user(ksig->sig, &frame->sig);
-	err |= __put_user(&frame->info, &frame->pinfo);
-	err |= __put_user(&frame->uc, &frame->puc);
 	err |= copy_siginfo_to_user(&frame->info, &ksig->info);
 
-	/* Create the ucontext.  */
+	/* Create the ucontext. */
 	err |= __put_user(0, &frame->uc.uc_flags);
-	err |= __put_user(0, &frame->uc.uc_link);
-	err |= __put_user((void *)current->sas_ss_sp,
-			&frame->uc.uc_stack.ss_sp);
-	err |= __put_user(sas_ss_flags(regs->usp),
-			&frame->uc.uc_stack.ss_flags);
-	err |= __put_user(current->sas_ss_size, &frame->uc.uc_stack.ss_size);
-	err |= setup_sigframe(&frame->uc.uc_mcontext, regs);
-	err |= copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));
-
+	err |= __put_user(NULL, &frame->uc.uc_link);
+	err |= __save_altstack(&frame->uc.uc_stack, regs->usp);
+	err |= setup_sigcontext(frame, regs);
+	err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));
 	if (err)
-		goto give_sigsegv;
+		return -EFAULT;
 
-	/* Set up registers for signal handler */
-	regs->usp = (unsigned long)frame;
-	regs->pc = (unsigned long)ksig->ka.sa.sa_handler;
-	regs->lr = (unsigned long)vdso->rt_signal_retcode;
+	/* Set up to return from userspace. */
+	regs->lr = (unsigned long)(vdso->rt_signal_retcode);
 
-adjust_stack:
-	regs->a0 = ksig->sig; /* first arg is signo */
-	regs->a1 = (unsigned long)(&(frame->info));
-	regs->a2 = (unsigned long)(&(frame->uc));
-	return err;
+	/*
+	 * Set up registers for signal handler.
+	 * Registers that we don't modify keep the value they had from
+	 * user-space at the time we took the signal.
+	 * We always pass siginfo and mcontext, regardless of SA_SIGINFO,
+	 * since some things rely on this (e.g. glibc's debug/segfault.c).
+	 */
+	regs->pc  = (unsigned long)ksig->ka.sa.sa_handler;
+	regs->usp = (unsigned long)frame;
+	regs->a0  = ksig->sig;				/* a0: signal number */
+	regs->a1  = (unsigned long)(&(frame->info));	/* a1: siginfo pointer */
+	regs->a2  = (unsigned long)(&(frame->uc));	/* a2: ucontext pointer */
 
-give_sigsegv:
-	if (ksig->sig == SIGSEGV)
-		ksig->ka.sa.sa_handler = SIG_DFL;
-	force_sig(SIGSEGV, current);
-	goto adjust_stack;
+	return 0;
 }
 
-/*
- * OK, we're invoking a handler
- */
-static int
-handle_signal(struct ksignal *ksig, struct pt_regs *regs)
+static void handle_signal(struct ksignal *ksig, struct pt_regs *regs)
 {
-	int ret;
 	sigset_t *oldset = sigmask_to_save();
+	int ret;
 
-	/*
-	 * set up the stack frame, regardless of SA_SIGINFO,
-	 * and pass info anyway.
-	 */
-	ret = setup_rt_frame(ksig, oldset, regs);
+	/* Are we from a system call? */
+	if (in_syscall(regs)) {
+		/* Avoid additional syscall restarting via ret_from_exception */
+		forget_syscall(regs);
+
+		/* If so, check system call restarting.. */
+		switch (regs->a0) {
+		case -ERESTART_RESTARTBLOCK:
+		case -ERESTARTNOHAND:
+			regs->a0 = -EINTR;
+			break;
 
-	if (ret != 0) {
-		force_sigsegv(ksig->sig, current);
-		return ret;
+		case -ERESTARTSYS:
+			if (!(ksig->ka.sa.sa_flags & SA_RESTART)) {
+				regs->a0 = -EINTR;
+				break;
+			}
+			/* fallthrough */
+		case -ERESTARTNOINTR:
+			regs->a0 = regs->orig_a0;
+			regs->pc -= TRAP0_SIZE;
+			break;
+		}
 	}
 
-	/* Block the signal if we were successful. */
-	spin_lock_irq(&current->sighand->siglock);
-	sigorsets(&current->blocked, &current->blocked, &ksig->ka.sa.sa_mask);
-	if (!(ksig->ka.sa.sa_flags & SA_NODEFER))
-		sigaddset(&current->blocked, ksig->sig);
-	recalc_sigpending();
-	spin_unlock_irq(&current->sighand->siglock);
+	/* Set up the stack frame */
+	ret = setup_rt_frame(ksig, oldset, regs);
 
-	return 0;
+	signal_setup_done(ret, ksig, 0);
 }
 
-/*
- * Note that 'init' is a special process: it doesn't get signals it doesn't
- * want to handle. Thus you cannot kill init even with a SIGKILL even by
- * mistake.
- *
- * Note that we go through the signals twice: once to check the signals
- * that the kernel can handle, and then we build all the user-level signal
- * handling stack-frames in one go after that.
- */
 static void do_signal(struct pt_regs *regs)
 {
-	unsigned int retval = 0, continue_addr = 0, restart_addr = 0;
 	struct ksignal ksig;
 
-	/*
-	 * We want the common case to go fast, which
-	 * is why we may in certain cases get here from
-	 * kernel mode. Just return without doing anything
-	 * if so.
-	 */
-	if (!user_mode(regs))
+	if (get_signal(&ksig)) {
+		/* Actually deliver the signal */
+		handle_signal(&ksig, regs);
 		return;
+	}
 
-	/*
-	 * If we were from a system call, check for system call restarting...
-	 */
+	/* Did we come from a system call? */
 	if (in_syscall(regs)) {
+		/* Avoid additional syscall restarting via ret_from_exception */
 		forget_syscall(regs);
 
-		continue_addr = regs->pc;
-#if defined(__CSKYABIV2__)
-		restart_addr = continue_addr - 4;
-#else
-		restart_addr = continue_addr - 2;
-#endif
-		retval = regs->a0;
-		/*
-		 * Prepare for system call restart.  We do this here so that a
-		 * debugger will see the already changed.
-		 */
-		switch (retval) {
+		/* Restart the system call - no handlers present */
+		switch (regs->a0) {
 		case -ERESTARTNOHAND:
 		case -ERESTARTSYS:
 		case -ERESTARTNOINTR:
 			regs->a0 = regs->orig_a0;
-			regs->pc = restart_addr;
+			regs->pc -= TRAP0_SIZE;
 			break;
 		case -ERESTART_RESTARTBLOCK:
-			regs->a0 = -EINTR;
+			regs->a0 = regs->orig_a0;
+			regs_syscallid(regs) = __NR_restart_syscall;
+			regs->pc -= TRAP0_SIZE;
 			break;
 		}
 	}
 
-	if (try_to_freeze())
-		goto no_signal;
-
 	/*
-	 * Get the signal to deliver.  When running under ptrace, at this
-	 * point the debugger may change all our registers ...
+	 * If there is no signal to deliver, we just put the saved
+	 * sigmask back.
 	 */
-	if (get_signal(&ksig)) {
-		/*
-		 * Depending on the signal settings we may need to revert the
-		 * decision to restart the system call.  But skip this if a
-		 * debugger has chosen to restart at a different PC.
-		 */
-		if (regs->pc == restart_addr) {
-			if (retval == -ERESTARTNOHAND ||
-			    (retval == -ERESTARTSYS &&
-			     !(ksig.ka.sa.sa_flags & SA_RESTART))) {
-				regs->a0 = -EINTR;
-				regs->pc = continue_addr;
-			}
-		}
-
-		/* Whee!  Actually deliver the signal.  */
-		if (handle_signal(&ksig, regs) == 0) {
-			/*
-			 * A signal was successfully delivered; the saved
-			 * sigmask will have been stored in the signal frame,
-			 * and will be restored by sigreturn, so we can simply
-			 * clear the TIF_RESTORE_SIGMASK flag.
-			 */
-			if (test_thread_flag(TIF_RESTORE_SIGMASK))
-				clear_thread_flag(TIF_RESTORE_SIGMASK);
-		}
-		return;
-	}
-
-no_signal:
-	if (in_syscall(regs)) {
-		forget_syscall(regs);
-
-		/*
-		 * Handle restarting a different system call.  As above,
-		 * if a debugger has chosen to restart at a different PC,
-		 * ignore the restart.
-		 */
-		if (retval == -ERESTART_RESTARTBLOCK
-				&& regs->pc == continue_addr) {
-#if defined(__CSKYABIV2__)
-			regs->regs[3] = __NR_restart_syscall;
-			regs->pc -= 4;
-#else
-			regs->regs[9] = __NR_restart_syscall;
-			regs->pc -= 2;
-#endif
-		}
-
-		/*
-		 * If there's no signal to deliver, we just put the saved
-		 * sigmask back.
-		 */
-		if (test_thread_flag(TIF_RESTORE_SIGMASK)) {
-			clear_thread_flag(TIF_RESTORE_SIGMASK);
-			sigprocmask(SIG_SETMASK, &current->saved_sigmask, NULL);
-		}
-	}
+	restore_saved_sigmask();
 }
 
-asmlinkage void
-do_notify_resume(unsigned int thread_flags, struct pt_regs *regs)
+/*
+ * notification of userspace execution resumption
+ * - triggered by the _TIF_WORK_MASK flags
+ */
+asmlinkage void do_notify_resume(struct pt_regs *regs,
+	unsigned long thread_info_flags)
 {
-	if (thread_flags & _TIF_SIGPENDING)
+	/* Handle pending signal delivery */
+	if (thread_info_flags & _TIF_SIGPENDING)
 		do_signal(regs);
 
-	if (thread_flags & _TIF_NOTIFY_RESUME) {
+	if (thread_info_flags & _TIF_NOTIFY_RESUME) {
 		clear_thread_flag(TIF_NOTIFY_RESUME);
 		tracehook_notify_resume(regs);
 	}