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Subject[PATCH 20/22] dynamic_debug: introduce CONFIG_DYNAMIC_DEBUG_RELATIVE_POINTERS
Date
Based on the same idea for struct bug_entry, an architecture can opt-in
to use relative pointers in struct _ddebug. It only makes sense for 64
bit architectures, where one saves 16 bytes per entry (out of 40 or 56,
depending on CONFIG_JUMP_LABEL). The architecture is responsible for
providing a suitable DEFINE_DYNAMIC_DEBUG_METADATA macro in
<asm/dynamic_debug.h>.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
include/linux/dynamic_debug.h | 14 ++++++++++++++
lib/Kconfig.debug | 3 +++
lib/dynamic_debug.c | 20 ++++++++++++++++++++
3 files changed, 37 insertions(+)

diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index e1be30e8422b..cc4222a20aa1 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -16,10 +16,17 @@ struct _ddebug {
* These fields are used to drive the user interface
* for selecting and displaying debug callsites.
*/
+#ifdef CONFIG_DYNAMIC_DEBUG_RELATIVE_POINTERS
+ signed int modname_disp;
+ signed int function_disp;
+ signed int filename_disp;
+ signed int format_disp;
+#else
const char *modname;
const char *function;
const char *filename;
const char *format;
+#endif
/*
* The flags field controls the behaviour at the callsite.
* The bits here are changed dynamically when the user
@@ -70,6 +77,12 @@ void __dynamic_netdev_dbg(struct _ddebug *descriptor,
const struct net_device *dev,
const char *fmt, ...);

+#ifdef CONFIG_DYNAMIC_DEBUG_RELATIVE_POINTERS
+#include <asm/dynamic_debug.h>
+#ifndef DEFINE_DYNAMIC_DEBUG_METADATA
+# error "asm/dynamic_debug.h must provide definition of DEFINE_DYNAMIC_DEBUG_METADATA"
+#endif
+#else
#define DEFINE_DYNAMIC_DEBUG_METADATA(name, fmt) \
static struct _ddebug __aligned(8) \
__attribute__((section("__verbose"))) name = { \
@@ -80,6 +93,7 @@ void __dynamic_netdev_dbg(struct _ddebug *descriptor,
.flags_lineno = _DPRINTK_FLAGS_LINENO_INIT, \
_DPRINTK_KEY_INIT \
}
+#endif

#ifdef HAVE_JUMP_LABEL

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 4966c4fbe7f7..a4113f746826 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -146,6 +146,9 @@ config DYNAMIC_DEBUG
See Documentation/admin-guide/dynamic-debug-howto.rst for additional
information.

+config DYNAMIC_DEBUG_RELATIVE_POINTERS
+ bool
+
endmenu # "printk and dmesg options"

menu "Compile-time checks and compiler options"
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index 9d4c840ff0de..61e61b36e479 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -37,6 +37,24 @@
#include <linux/device.h>
#include <linux/netdevice.h>

+#ifdef CONFIG_DYNAMIC_DEBUG_RELATIVE_POINTERS
+static inline const char *dd_modname(const struct _ddebug *dd)
+{
+ return (const char *)dd + dd->modname_disp;
+}
+static inline const char *dd_function(const struct _ddebug *dd)
+{
+ return (const char *)dd + dd->function_disp;
+}
+static inline const char *dd_filename(const struct _ddebug *dd)
+{
+ return (const char *)dd + dd->filename_disp;
+}
+static inline const char *dd_format(const struct _ddebug *dd)
+{
+ return (const char *)dd + dd->format_disp;
+}
+#else
static inline const char *dd_modname(const struct _ddebug *dd)
{
return dd->modname;
@@ -53,6 +71,8 @@ static inline const char *dd_format(const struct _ddebug *dd)
{
return dd->format;
}
+#endif
+
static inline unsigned dd_lineno(const struct _ddebug *dd)
{
return dd->flags_lineno >> 8;
--
2.16.4
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