ARCv2: save ABI registers across signal handling

ARCv2 has some configuration dependent registers (r30, r58, r59) which
could be targetted by the compiler. To keep the ABI stable, these were
unconditionally part of the glibc ABI
(sysdeps/unix/sysv/linux/arc/sys/ucontext.h:mcontext_t) however we
missed populating them (by saving/restoring them across signal
handling).

This patch fixes the issue by
 - adding arcv2 ABI regs to kernel struct sigcontext
 - populating them during signal handling

Change to struct sigcontext might seem like a glibc ABI change (although
it primarily uses ucontext_t:mcontext_t) but the fact is
 - it has only been extended (existing fields are not touched)
 - the old sigcontext was ABI incomplete to begin with anyways

Fixes: https://github.com/foss-for-synopsys-dwc-arc-processors/linux/issues/53
Cc: <stable@vger.kernel.org>
Tested-by: kernel test robot <lkp@intel.com>
Reported-by: Vladimir Isaev <isaev@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

arch/arc/include/uapi/asm/sigcontext.h

@@ -18,6 +18,7 @@
  */
 struct sigcontext {
 	struct user_regs_struct regs;
+	struct user_regs_arcv2 v2abi;
 };
 
 #endif /* _ASM_ARC_SIGCONTEXT_H */

arch/arc/kernel/signal.c

@@ -61,6 +61,41 @@ struct rt_sigframe {
 	unsigned int sigret_magic;
 };
 
+static int save_arcv2_regs(struct sigcontext *mctx, struct pt_regs *regs)
+{
+	int err = 0;
+#ifndef CONFIG_ISA_ARCOMPACT
+	struct user_regs_arcv2 v2abi;
+
+	v2abi.r30 = regs->r30;
+#ifdef CONFIG_ARC_HAS_ACCL_REGS
+	v2abi.r58 = regs->r58;
+	v2abi.r59 = regs->r59;
+#else
+	v2abi.r58 = v2abi.r59 = 0;
+#endif
+	err = __copy_to_user(&mctx->v2abi, &v2abi, sizeof(v2abi));
+#endif
+	return err;
+}
+
+static int restore_arcv2_regs(struct sigcontext *mctx, struct pt_regs *regs)
+{
+	int err = 0;
+#ifndef CONFIG_ISA_ARCOMPACT
+	struct user_regs_arcv2 v2abi;
+
+	err = __copy_from_user(&v2abi, &mctx->v2abi, sizeof(v2abi));
+
+	regs->r30 = v2abi.r30;
+#ifdef CONFIG_ARC_HAS_ACCL_REGS
+	regs->r58 = v2abi.r58;
+	regs->r59 = v2abi.r59;
+#endif
+#endif
+	return err;
+}
+
 static int
 stash_usr_regs(struct rt_sigframe __user *sf, struct pt_regs *regs,
 	       sigset_t *set)
@@ -94,6 +129,10 @@ stash_usr_regs(struct rt_sigframe __user *sf, struct pt_regs *regs,
 
 	err = __copy_to_user(&(sf->uc.uc_mcontext.regs.scratch), &uregs.scratch,
 			     sizeof(sf->uc.uc_mcontext.regs.scratch));
+
+	if (is_isa_arcv2())
+		err |= save_arcv2_regs(&(sf->uc.uc_mcontext), regs);
+
 	err |= __copy_to_user(&sf->uc.uc_sigmask, set, sizeof(sigset_t));
 
 	return err ? -EFAULT : 0;
@@ -109,6 +148,10 @@ static int restore_usr_regs(struct pt_regs *regs, struct rt_sigframe __user *sf)
 	err |= __copy_from_user(&uregs.scratch,
 				&(sf->uc.uc_mcontext.regs.scratch),
 				sizeof(sf->uc.uc_mcontext.regs.scratch));
+
+	if (is_isa_arcv2())
+		err |= restore_arcv2_regs(&(sf->uc.uc_mcontext), regs);
+
 	if (err)
 		return -EFAULT;