build: prepare for -Wimplicit-fallthrough=5

* gcc_compat.h (ATTRIBUTE_FALLTHROUGH): New macro.
* block.c (block_ioctl): Use it instead of "fall through" comment.
* btrfs.c (btrfs_ioctl): Likewise.
* loop.c (loop_ioctl): Likewise.
* mtd.c (mtd_ioctl): Likewise.
* rtc.c (rtc_ioctl): Likewise.
* v4l2.c (v4l2_ioctl): Likewise.
* dm.c (dm_decode_values): Likewise.
* process.c (SYS_FUNC(ptrace)): Likewise.
* quota.c (decode_cmd_data): Likewise.
* ucopy.c (umovestr): Likewise.
* unwind.c (unwind_print_stacktrace, unwind_capture_stacktrace)):
Likewise.
* term.c (term_ioctl): Add ATTRIBUTE_FALLTHROUGH.
* ioctl.c (ioctl_decode) [ALPHA || POWERPC]: Likewise.
* m4/st_warn_cflags.m4 (gl_WARN_ADD): Add -Wimplicit-fallthrough=5.
* tests/ioctl_v4l2.c (init_v4l2_format): Reorganize the switch statement
without implicit fallthrough.

16 files changed, 41 insertions, 24 deletions

diff --git a/block.c b/block.c
index b402f6835..f31ef1428 100644
--- a/block.c
+++ b/block.c
@@ -168,7 +168,7 @@ MPERS_PRINTER_DECL(int, block_ioctl, struct tcb *const tcp,
 	case BLKALIGNOFF:
 		if (entering(tcp))
 			return 0;
-		/* fall through */
+		ATTRIBUTE_FALLTHROUGH;
 	/* take a signed int */
 	case BLKROSET:
 	case BLKBSZSET:
diff --git a/btrfs.c b/btrfs.c
index ed3120ae3..3016ec843 100644
--- a/btrfs.c
+++ b/btrfs.c
@@ -538,7 +538,7 @@ MPERS_PRINTER_DECL(int, btrfs_ioctl,
 	case BTRFS_IOC_START_SYNC: /* R */
 		if (entering(tcp))
 			return 0;
-	/* fall through */
+	ATTRIBUTE_FALLTHROUGH;
 	/* takes a u64 */
 	case BTRFS_IOC_DEFAULT_SUBVOL: /* W */
 	case BTRFS_IOC_WAIT_SYNC: /* W */
@@ -1318,7 +1318,7 @@ MPERS_PRINTER_DECL(int, btrfs_ioctl,
 	case BTRFS_IOC_GET_FSLABEL: /* R */
 		if (entering(tcp))
 			return 0;
-		/* fall through */
+		ATTRIBUTE_FALLTHROUGH;
 	case BTRFS_IOC_SET_FSLABEL: { /* W */
 		char label[BTRFS_LABEL_SIZE];
 
diff --git a/dm.c b/dm.c
index 32b331011..17470fa1e 100644
--- a/dm.c
+++ b/dm.c
@@ -91,7 +91,7 @@ dm_decode_values(struct tcb *tcp, const unsigned int code,
 		case DM_DEV_SUSPEND:
 			if (ioc->flags & DM_SUSPEND_FLAG)
 				break;
-			/* Fall through */
+			ATTRIBUTE_FALLTHROUGH;
 		case DM_DEV_RENAME:
 		case DM_DEV_REMOVE:
 		case DM_DEV_WAIT:
diff --git a/gcc_compat.h b/gcc_compat.h
index 956aff176..b55092fd9 100644
--- a/gcc_compat.h
+++ b/gcc_compat.h
@@ -93,4 +93,10 @@
 # define ATTRIBUTE_ALLOC_SIZE(args)	/* empty */
 #endif
 
+#if GNUC_PREREQ(7, 0)
+# define ATTRIBUTE_FALLTHROUGH	__attribute__((__fallthrough__))
+#else
+# define ATTRIBUTE_FALLTHROUGH	((void) 0)
+#endif
+
 #endif /* !STRACE_GCC_COMPAT_H */
diff --git a/ioctl.c b/ioctl.c
index 9fd74924f..5a59f379e 100644
--- a/ioctl.c
+++ b/ioctl.c
@@ -263,6 +263,7 @@ ioctl_decode(struct tcb *tcp)
 		int ret = file_ioctl(tcp, code, arg);
 		if (ret != RVAL_DECODED)
 			return ret;
+		ATTRIBUTE_FALLTHROUGH;
 	}
 	case 't':
 	case 'T':
diff --git a/loop.c b/loop.c
index 33bd03857..291f5646c 100644
--- a/loop.c
+++ b/loop.c
@@ -156,7 +156,7 @@ MPERS_PRINTER_DECL(int, loop_ioctl,
 	case LOOP_GET_STATUS:
 		if (entering(tcp))
 			return 0;
-		/* fall through */
+		ATTRIBUTE_FALLTHROUGH;
 	case LOOP_SET_STATUS:
 		decode_loop_info(tcp, arg);
 		break;
@@ -164,7 +164,7 @@ MPERS_PRINTER_DECL(int, loop_ioctl,
 	case LOOP_GET_STATUS64:
 		if (entering(tcp))
 			return 0;
-		/* fall through */
+		ATTRIBUTE_FALLTHROUGH;
 	case LOOP_SET_STATUS64:
 		decode_loop_info64(tcp, arg);
 		break;
diff --git a/m4/st_warn_cflags.m4 b/m4/st_warn_cflags.m4
index 04d45442d..35f40b589 100644
--- a/m4/st_warn_cflags.m4
+++ b/m4/st_warn_cflags.m4
@@ -3,6 +3,7 @@ gl_WARN_ADD([-Wall])
 gl_WARN_ADD([-Wempty-body])
 gl_WARN_ADD([-Wformat-security])
 gl_WARN_ADD([-Wignored-qualifiers])
+gl_WARN_ADD([-Wimplicit-fallthrough=5])
 gl_WARN_ADD([-Winit-self])
 gl_WARN_ADD([-Wlogical-op])
 gl_WARN_ADD([-Wmissing-parameter-type])
diff --git a/mtd.c b/mtd.c
index 52957f9d3..cf4e30c3d 100644
--- a/mtd.c
+++ b/mtd.c
@@ -274,7 +274,7 @@ MPERS_PRINTER_DECL(int, mtd_ioctl, struct tcb *const tcp,
 	case OTPGETREGIONINFO:
 		if (entering(tcp))
 			return 0;
-		/* fall through */
+		ATTRIBUTE_FALLTHROUGH;
 	case OTPLOCK:
 		decode_otp_info(tcp, arg);
 		break;
diff --git a/process.c b/process.c
index 895fc4b8f..f5733417c 100644
--- a/process.c
+++ b/process.c
@@ -219,7 +219,7 @@ SYS_FUNC(ptrace)
 				/* print data on exiting syscall */
 				return 0;
 			}
-			/* fall through */
+			ATTRIBUTE_FALLTHROUGH;
 		default:
 			printaddr(data);
 			break;
diff --git a/quota.c b/quota.c
index ba1d7612a..a051bd883 100644
--- a/quota.c
+++ b/quota.c
@@ -177,7 +177,7 @@ decode_cmd_data(struct tcb *tcp, uint32_t id, uint32_t cmd, kernel_ulong_t data)
 			return 0;
 		}
 
-		/* Fall-through */
+		ATTRIBUTE_FALLTHROUGH;
 	case Q_SETQUOTA:
 	{
 		struct if_dqblk dq;
@@ -247,7 +247,7 @@ decode_cmd_data(struct tcb *tcp, uint32_t id, uint32_t cmd, kernel_ulong_t data)
 			return 0;
 		}
 
-		/* Fall-through */
+		ATTRIBUTE_FALLTHROUGH;
 	case Q_XSETQLIM:
 	{
 		struct xfs_dqblk dq;
@@ -310,7 +310,7 @@ decode_cmd_data(struct tcb *tcp, uint32_t id, uint32_t cmd, kernel_ulong_t data)
 			return 0;
 		}
 
-		/* Fall-through */
+		ATTRIBUTE_FALLTHROUGH;
 	case Q_SETINFO:
 	{
 		struct if_dqinfo dq;
diff --git a/rtc.c b/rtc.c
index 9c02cbd50..b5c65da9f 100644
--- a/rtc.c
+++ b/rtc.c
@@ -93,7 +93,7 @@ MPERS_PRINTER_DECL(int, rtc_ioctl, struct tcb *const tcp,
 	case RTC_RD_TIME:
 		if (entering(tcp))
 			return 0;
-		/* fall through */
+		ATTRIBUTE_FALLTHROUGH;
 	case RTC_ALM_SET:
 	case RTC_SET_TIME:
 		tprints(", ");
@@ -113,7 +113,7 @@ MPERS_PRINTER_DECL(int, rtc_ioctl, struct tcb *const tcp,
 	case RTC_WKALM_RD:
 		if (entering(tcp))
 			return 0;
-		/* fall through */
+		ATTRIBUTE_FALLTHROUGH;
 	case RTC_WKALM_SET:
 		tprints(", ");
 		decode_rtc_wkalrm(tcp, arg);
@@ -121,7 +121,7 @@ MPERS_PRINTER_DECL(int, rtc_ioctl, struct tcb *const tcp,
 	case RTC_PLL_GET:
 		if (entering(tcp))
 			return 0;
-		/* fall through */
+		ATTRIBUTE_FALLTHROUGH;
 	case RTC_PLL_SET:
 		tprints(", ");
 		decode_rtc_pll_info(tcp, arg);
diff --git a/term.c b/term.c
index 9368e5fd5..0f13f5f11 100644
--- a/term.c
+++ b/term.c
@@ -160,6 +160,7 @@ term_ioctl(struct tcb *const tcp, const unsigned int code,
 	case TIOCGLCKTRMIOS:
 		if (entering(tcp))
 			return 0;
+		ATTRIBUTE_FALLTHROUGH;
 	case TCSETS:
 #ifdef TCSETS2
 	case TCSETS2:
@@ -180,6 +181,7 @@ term_ioctl(struct tcb *const tcp, const unsigned int code,
 	case TCGETA:
 		if (entering(tcp))
 			return 0;
+		ATTRIBUTE_FALLTHROUGH;
 	case TCSETA:
 	case TCSETAW:
 	case TCSETAF:
@@ -190,6 +192,7 @@ term_ioctl(struct tcb *const tcp, const unsigned int code,
 	case TIOCGWINSZ:
 		if (entering(tcp))
 			return 0;
+		ATTRIBUTE_FALLTHROUGH;
 	case TIOCSWINSZ:
 		decode_winsize(tcp, arg);
 		break;
@@ -199,6 +202,7 @@ term_ioctl(struct tcb *const tcp, const unsigned int code,
 	case TIOCGSIZE:
 		if (entering(tcp))
 			return 0;
+		ATTRIBUTE_FALLTHROUGH;
 	case TIOCSSIZE:
 		decode_ttysize(tcp, arg);
 		break;
@@ -223,6 +227,7 @@ term_ioctl(struct tcb *const tcp, const unsigned int code,
 	case TIOCMGET:
 		if (entering(tcp))
 			return 0;
+		ATTRIBUTE_FALLTHROUGH;
 	case TIOCMBIS:
 	case TIOCMBIC:
 	case TIOCMSET:
@@ -245,6 +250,7 @@ term_ioctl(struct tcb *const tcp, const unsigned int code,
 #endif
 		if (entering(tcp))
 			return 0;
+		ATTRIBUTE_FALLTHROUGH;
 	case TIOCSPGRP:
 	case TIOCSETD:
 	case FIONBIO:
diff --git a/tests/ioctl_v4l2.c b/tests/ioctl_v4l2.c
index 8cf22777c..4b7a1262a 100644
--- a/tests/ioctl_v4l2.c
+++ b/tests/ioctl_v4l2.c
@@ -157,14 +157,17 @@ init_v4l2_format(struct v4l2_format *const f,
 #if HAVE_DECL_V4L2_BUF_TYPE_SDR_OUTPUT
 	case V4L2_BUF_TYPE_SDR_OUTPUT:
 		f->fmt.sdr.pixelformat = sf_magic;
+# ifdef HAVE_STRUCT_V4L2_SDR_FORMAT_BUFFERSIZE
+		f->fmt.sdr.buffersize = 0x25afabfb;
+# endif
+		break;
 #endif
 #if HAVE_DECL_V4L2_BUF_TYPE_SDR_CAPTURE
 	case V4L2_BUF_TYPE_SDR_CAPTURE:
-		if (buf_type == V4L2_BUF_TYPE_SDR_CAPTURE)
-			f->fmt.sdr.pixelformat = magic;
-#ifdef HAVE_STRUCT_V4L2_SDR_FORMAT_BUFFERSIZE
+		f->fmt.sdr.pixelformat = magic;
+# ifdef HAVE_STRUCT_V4L2_SDR_FORMAT_BUFFERSIZE
 		f->fmt.sdr.buffersize = 0x25afabfb;
-#endif
+# endif
 		break;
 #endif
 	}
diff --git a/ucopy.c b/ucopy.c
index 2d9ffb38c..a31f5243c 100644
--- a/ucopy.c
+++ b/ucopy.c
@@ -306,7 +306,7 @@ umovestr(struct tcb *const tcp, kernel_ulong_t addr, unsigned int len,
 				if (!nread)
 					return umovestr_peekdata(pid, addr,
 								 len, laddr);
-				/* fall through */
+				ATTRIBUTE_FALLTHROUGH;
 			case EFAULT: case EIO:
 				/* address space is inaccessible */
 				if (nread)
diff --git a/unwind.c b/unwind.c
index cbb5206bc..a272fba8f 100644
--- a/unwind.c
+++ b/unwind.c
@@ -398,7 +398,7 @@ unwind_print_stacktrace(struct tcb *tcp)
 	} else switch (mmap_cache_rebuild_if_invalid(tcp, __func__)) {
 		case MMAP_CACHE_REBUILD_RENEWED:
 			unw_flush_cache(libunwind_as, 0, 0);
-			/* Fall through */
+			ATTRIBUTE_FALLTHROUGH;
 		case MMAP_CACHE_REBUILD_READY:
 			debug_func_msg("walk: tcp=%p, queue=%p", tcp, tcp->queue->head);
 			stacktrace_walk(tcp, print_call_cb, print_error_cb, NULL);
@@ -427,7 +427,7 @@ unwind_capture_stacktrace(struct tcb *tcp)
 	switch (mmap_cache_rebuild_if_invalid(tcp, __func__)) {
 	case MMAP_CACHE_REBUILD_RENEWED:
 		unw_flush_cache(libunwind_as, 0, 0);
-		/* Fall through */
+		ATTRIBUTE_FALLTHROUGH;
 	case MMAP_CACHE_REBUILD_READY:
 		stacktrace_walk(tcp, queue_put_call, queue_put_error,
 				tcp->queue);
diff --git a/v4l2.c b/v4l2.c
index 41f62c7f8..7081c81cc 100644
--- a/v4l2.c
+++ b/v4l2.c
@@ -1022,7 +1022,7 @@ MPERS_PRINTER_DECL(int, v4l2_ioctl, struct tcb *const tcp,
 	case VIDIOC_G_FBUF: /* R */
 		if (entering(tcp))
 			return 0;
-		/* fall through */
+		ATTRIBUTE_FALLTHROUGH;
 	case VIDIOC_S_FBUF: /* W */
 		return print_v4l2_framebuffer(tcp, arg);
 
@@ -1037,7 +1037,7 @@ MPERS_PRINTER_DECL(int, v4l2_ioctl, struct tcb *const tcp,
 	case VIDIOC_G_STD: /* R */
 		if (entering(tcp))
 			return 0;
-		/* fall through */
+		ATTRIBUTE_FALLTHROUGH;
 	case VIDIOC_S_STD: /* W */
 		tprints(", ");
 		printnum_int64(tcp, arg, "%#" PRIx64);
@@ -1063,7 +1063,7 @@ MPERS_PRINTER_DECL(int, v4l2_ioctl, struct tcb *const tcp,
 	case VIDIOC_G_INPUT: /* R */
 		if (entering(tcp))
 			return 0;
-		/* fall through */
+		ATTRIBUTE_FALLTHROUGH;
 	case VIDIOC_S_INPUT: /* RW */
 		tprints(", ");
 		printnum_int(tcp, arg, "%u");