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Date:   Thu, 28 Feb 2019 13:27:46 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Cc:     linux-kernel@...r.kernel.org,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Andy Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: [PATCH v2] x86/syscalls: Mark expected switch fall-throughs

In preparation to enable -Wimplicit-fallthrough by default, mark
switch-case statements where fall-through is intentional, explicitly
in order to fix a bunch of -Wimplicit-fallthrough warnings.

In order to get the warnings mentioned above, the following
line was added to the top Makefile:

KBUILD_CFLAGS  += $(call cc-option,-Wimplicit-fallthrough=3,)

Reviewed-by: Kees Cook <keescook@...omium.org>
Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
---
Changes in v2:
 - Expand commit text as requested by Thomas Gleixner.
 - Add Kees' Reviewed-by.

 arch/x86/include/asm/syscall.h | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/arch/x86/include/asm/syscall.h b/arch/x86/include/asm/syscall.h
index d653139857af..04fc5c120558 100644
--- a/arch/x86/include/asm/syscall.h
+++ b/arch/x86/include/asm/syscall.h
@@ -125,23 +125,30 @@ static inline void syscall_get_arguments(struct task_struct *task,
 		case 0:
 			if (!n--) break;
 			*args++ = regs->bx;
+			/* fall through */
 		case 1:
 			if (!n--) break;
 			*args++ = regs->cx;
+			/* fall through */
 		case 2:
 			if (!n--) break;
 			*args++ = regs->dx;
+			/* fall through */
 		case 3:
 			if (!n--) break;
 			*args++ = regs->si;
+			/* fall through */
 		case 4:
 			if (!n--) break;
 			*args++ = regs->di;
+			/* fall through */
 		case 5:
 			if (!n--) break;
 			*args++ = regs->bp;
+			/* fall through */
 		case 6:
 			if (!n--) break;
+			/* fall through */
 		default:
 			BUG();
 			break;
@@ -152,23 +159,30 @@ static inline void syscall_get_arguments(struct task_struct *task,
 		case 0:
 			if (!n--) break;
 			*args++ = regs->di;
+			/* fall through */
 		case 1:
 			if (!n--) break;
 			*args++ = regs->si;
+			/* fall through */
 		case 2:
 			if (!n--) break;
 			*args++ = regs->dx;
+			/* fall through */
 		case 3:
 			if (!n--) break;
 			*args++ = regs->r10;
+			/* fall through */
 		case 4:
 			if (!n--) break;
 			*args++ = regs->r8;
+			/* fall through */
 		case 5:
 			if (!n--) break;
 			*args++ = regs->r9;
+			/* fall through */
 		case 6:
 			if (!n--) break;
+			/* fall through */
 		default:
 			BUG();
 			break;
@@ -186,23 +200,30 @@ static inline void syscall_set_arguments(struct task_struct *task,
 		case 0:
 			if (!n--) break;
 			regs->bx = *args++;
+			/* fall through */
 		case 1:
 			if (!n--) break;
 			regs->cx = *args++;
+			/* fall through */
 		case 2:
 			if (!n--) break;
 			regs->dx = *args++;
+			/* fall through */
 		case 3:
 			if (!n--) break;
 			regs->si = *args++;
+			/* fall through */
 		case 4:
 			if (!n--) break;
 			regs->di = *args++;
+			/* fall through */
 		case 5:
 			if (!n--) break;
 			regs->bp = *args++;
+			/* fall through */
 		case 6:
 			if (!n--) break;
+			/* fall through */
 		default:
 			BUG();
 			break;
@@ -213,23 +234,30 @@ static inline void syscall_set_arguments(struct task_struct *task,
 		case 0:
 			if (!n--) break;
 			regs->di = *args++;
+			/* fall through */
 		case 1:
 			if (!n--) break;
 			regs->si = *args++;
+			/* fall through */
 		case 2:
 			if (!n--) break;
 			regs->dx = *args++;
+			/* fall through */
 		case 3:
 			if (!n--) break;
 			regs->r10 = *args++;
+			/* fall through */
 		case 4:
 			if (!n--) break;
 			regs->r8 = *args++;
+			/* fall through */
 		case 5:
 			if (!n--) break;
 			regs->r9 = *args++;
+			/* fall through */
 		case 6:
 			if (!n--) break;
+			/* fall through */
 		default:
 			BUG();
 			break;
-- 
2.21.0

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