[PATCH] ARCv2: save ABI registers across signal handling

[Vineet Gupta]

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 at vger.kernel.org>
Reported-by: Vladimir Isaev <isaev at synopsys.com>
Signed-off-by: Vineet Gupta <vgupta at synopsys.com>
---
 arch/arc/include/uapi/asm/sigcontext.h |  1 +
 arch/arc/kernel/signal.c               | 29 ++++++++++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/arch/arc/include/uapi/asm/sigcontext.h b/arch/arc/include/uapi/asm/sigcontext.h
index 95f8a4380e11..7a5449dfcb29 100644
--- a/arch/arc/include/uapi/asm/sigcontext.h
+++ b/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 */
diff --git a/arch/arc/kernel/signal.c b/arch/arc/kernel/signal.c
index b3ccb9e5ffe4..534b3d9bafc8 100644
--- a/arch/arc/kernel/signal.c
+++ b/arch/arc/kernel/signal.c
@@ -94,6 +94,21 @@ 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()) {
+		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(&(sf->uc.uc_mcontext.v2abi), &v2abi,
+				      sizeof(sf->uc.uc_mcontext.v2abi));
+	}
+
 	err |= __copy_to_user(&sf->uc.uc_sigmask, set, sizeof(sigset_t));
 
 	return err ? -EFAULT : 0;
@@ -109,6 +124,20 @@ 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()) {
+		struct user_regs_arcv2 v2abi;
+
+		err |= __copy_from_user(&v2abi,	&(sf->uc.uc_mcontext.v2abi),
+					sizeof(sf->uc.uc_mcontext.v2abi));
+
+		regs->r30 = v2abi.r30;
+#ifdef CONFIG_ARC_HAS_ACCL_REGS
+		regs->r58 = v2abi.r58;
+		regs->r59 = v2abi.r59;
+#endif
+	}
+
 	if (err)
 		return -EFAULT;
 
-- 
2.25.1