[PATCH v6 5/8] dynamic_debug: drop use of bitfields in struct _ddebug

[Rasmus Villemoes <linux@rasmusvillemoes.dk>]

Properly initializing a struct containing bitfields in assembly is
hard. Instead, merge lineno and flags to a single unsigned int, which we
mask manually. This should not cause any worse code than what gcc would
need to generate for accessing the bitfields anyway.

Actually, on 64 bit, there is a four byte hole after these fields, so we
could just give flags and lineno each their own u32. But I don't think
that's worth the ifdeffery.

Acked-by: Jason Baron <jbaron@akamai.com>
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
 include/linux/dynamic_debug.h | 12 ++++------
 lib/dynamic_debug.c           | 44 +++++++++++++++++++++++------------
 2 files changed, 34 insertions(+), 22 deletions(-)

diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index 6c809440f319..7d6d0153096e 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -20,7 +20,6 @@ struct _ddebug {
 	const char *function;
 	const char *filename;
 	const char *format;
-	unsigned int lineno:18;
 	/*
 	 * The flags field controls the behaviour at the callsite.
 	 * The bits here are changed dynamically when the user
@@ -37,7 +36,7 @@ struct _ddebug {
 #else
 #define _DPRINTK_FLAGS_DEFAULT 0
 #endif
-	unsigned int flags:8;
+	unsigned int flags_lineno; /* flags in lower 8 bits, lineno in upper 24 */
 #ifdef CONFIG_JUMP_LABEL
 	union {
 		struct static_key_true dd_key_true;
@@ -46,7 +45,7 @@ struct _ddebug {
 #endif
 } __attribute__((aligned(8)));
 
-
+#define _DPRINTK_FLAGS_LINENO_INIT (((unsigned)__LINE__ << 8) | _DPRINTK_FLAGS_DEFAULT)
 
 #if defined(CONFIG_DYNAMIC_DEBUG)
 int ddebug_add_module(struct _ddebug *tab, unsigned int n,
@@ -85,8 +84,7 @@ void __dynamic_ibdev_dbg(struct _ddebug *descriptor,
 		.function = __func__,				\
 		.filename = __FILE__,				\
 		.format = (fmt),				\
-		.lineno = __LINE__,				\
-		.flags = _DPRINTK_FLAGS_DEFAULT,		\
+		.flags_lineno = _DPRINTK_FLAGS_LINENO_INIT,	\
 		_DPRINTK_KEY_INIT				\
 	}
 
@@ -111,10 +109,10 @@ void __dynamic_ibdev_dbg(struct _ddebug *descriptor,
 
 #ifdef DEBUG
 #define DYNAMIC_DEBUG_BRANCH(descriptor) \
-	likely(descriptor.flags & _DPRINTK_FLAGS_PRINT)
+	likely(descriptor.flags_lineno & _DPRINTK_FLAGS_PRINT)
 #else
 #define DYNAMIC_DEBUG_BRANCH(descriptor) \
-	unlikely(descriptor.flags & _DPRINTK_FLAGS_PRINT)
+	unlikely(descriptor.flags_lineno & _DPRINTK_FLAGS_PRINT)
 #endif
 
 #endif
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index 3599c4c0361a..3a1a80041cd6 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -55,6 +55,18 @@ static inline const char *dd_format(const struct _ddebug *dd)
 {
 	return dd->format;
 }
+static inline unsigned dd_lineno(const struct _ddebug *dd)
+{
+	return dd->flags_lineno >> 8;
+}
+static inline unsigned dd_flags(const struct _ddebug *dd)
+{
+	return dd->flags_lineno & 0xff;
+}
+static inline void dd_set_flags(struct _ddebug *dd, unsigned newflags)
+{
+	dd->flags_lineno = (dd_lineno(dd) << 8) | newflags;
+}
 
 extern struct _ddebug __start___verbose[];
 extern struct _ddebug __stop___verbose[];
@@ -113,7 +125,7 @@ static char *ddebug_describe_flags(struct _ddebug *dp, char *buf,
 
 	BUG_ON(maxlen < 6);
 	for (i = 0; i < ARRAY_SIZE(opt_array); ++i)
-		if (dp->flags & opt_array[i].flag)
+		if (dd_flags(dp) & opt_array[i].flag)
 			*p++ = opt_array[i].opt_char;
 	if (p == buf)
 		*p++ = '_';
@@ -159,7 +171,7 @@ static int ddebug_change(const struct ddebug_query *query,
 {
 	int i;
 	struct ddebug_table *dt;
-	unsigned int newflags;
+	unsigned int newflags, oldflags;
 	unsigned int nfound = 0;
 	char flagbuf[10];
 
@@ -196,27 +208,28 @@ static int ddebug_change(const struct ddebug_query *query,
 
 			/* match against the line number range */
 			if (query->first_lineno &&
-			    dp->lineno < query->first_lineno)
+			    dd_lineno(dp) < query->first_lineno)
 				continue;
 			if (query->last_lineno &&
-			    dp->lineno > query->last_lineno)
+			    dd_lineno(dp) > query->last_lineno)
 				continue;
 
 			nfound++;
 
-			newflags = (dp->flags & mask) | flags;
-			if (newflags == dp->flags)
+			oldflags = dd_flags(dp);
+			newflags = (oldflags & mask) | flags;
+			if (newflags == oldflags)
 				continue;
 #ifdef CONFIG_JUMP_LABEL
-			if (dp->flags & _DPRINTK_FLAGS_PRINT) {
+			if (oldflags & _DPRINTK_FLAGS_PRINT) {
 				if (!(flags & _DPRINTK_FLAGS_PRINT))
 					static_branch_disable(&dp->key.dd_key_true);
 			} else if (flags & _DPRINTK_FLAGS_PRINT)
 				static_branch_enable(&dp->key.dd_key_true);
 #endif
-			dp->flags = newflags;
+			dd_set_flags(dp, newflags);
 			vpr_info("changed %s:%d [%s]%s =%s\n",
-				 trim_prefix(dd_filename(dp)), dp->lineno,
+				 trim_prefix(dd_filename(dp)), dd_lineno(dp),
 				 dt->mod_name, dd_function(dp),
 				 ddebug_describe_flags(dp, flagbuf,
 						       sizeof(flagbuf)));
@@ -539,10 +552,11 @@ static char *dynamic_emit_prefix(const struct _ddebug *desc, char *buf)
 {
 	int pos_after_tid;
 	int pos = 0;
+	unsigned flags = dd_flags(desc);
 
 	*buf = '\0';
 
-	if (desc->flags & _DPRINTK_FLAGS_INCL_TID) {
+	if (flags & _DPRINTK_FLAGS_INCL_TID) {
 		if (in_interrupt())
 			pos += snprintf(buf + pos, remaining(pos), "<intr> ");
 		else
@@ -550,15 +564,15 @@ static char *dynamic_emit_prefix(const struct _ddebug *desc, char *buf)
 					task_pid_vnr(current));
 	}
 	pos_after_tid = pos;
-	if (desc->flags & _DPRINTK_FLAGS_INCL_MODNAME)
+	if (flags & _DPRINTK_FLAGS_INCL_MODNAME)
 		pos += snprintf(buf + pos, remaining(pos), "%s:",
 				dd_modname(desc));
-	if (desc->flags & _DPRINTK_FLAGS_INCL_FUNCNAME)
+	if (flags & _DPRINTK_FLAGS_INCL_FUNCNAME)
 		pos += snprintf(buf + pos, remaining(pos), "%s:",
 				dd_function(desc));
-	if (desc->flags & _DPRINTK_FLAGS_INCL_LINENO)
+	if (flags & _DPRINTK_FLAGS_INCL_LINENO)
 		pos += snprintf(buf + pos, remaining(pos), "%d:",
-				desc->lineno);
+				dd_lineno(desc));
 	if (pos - pos_after_tid)
 		pos += snprintf(buf + pos, remaining(pos), " ");
 	if (pos >= PREFIX_SIZE)
@@ -844,7 +858,7 @@ static int ddebug_proc_show(struct seq_file *m, void *p)
 	}
 
 	seq_printf(m, "%s:%u [%s]%s =%s \"",
-		   trim_prefix(dd_filename(dp)), dp->lineno,
+		   trim_prefix(dd_filename(dp)), dd_lineno(dp),
 		   iter->table->mod_name, dd_function(dp),
 		   ddebug_describe_flags(dp, flagsbuf, sizeof(flagsbuf)));
 	seq_escape(m, dd_format(dp), "\t\r\n\"");
-- 
2.20.1