Commit 9049fc74 authored by Jason Baron's avatar Jason Baron Committed by Linus Torvalds
Browse files

dynamic_debug: add jump label support 

Although dynamic debug is often only used for debug builds, sometimes
its enabled for production builds as well.  Minimize its impact by using
jump labels.  This reduces the text section by 7000+ bytes in the kernel
image below.  It does increase data, but this should only be referenced
when changing the direction of the branches, and hence usually not in
cache.

     text     data     bss       dec     hex  filename
  8194852  4879776  925696  14000324  d5a0c4  vmlinux.pre
  8187337  4960224  925696  14073257  d6bda9  vmlinux.post

Link: http://lkml.kernel.org/r/d165b465e8c89bc582d973758d40be44c33f018b.1467837322.git.jbaron@akamai.com


Signed-off-by: default avatarJason Baron <jbaron@akamai.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Joe Perches <joe@perches.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 1f69bf9c

include/linux/dynamic_debug.h

+54 −6
Original line number Diff line number Diff line 
#ifndef _DYNAMIC_DEBUG_H

#define _DYNAMIC_DEBUG_H



#if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)

#include <linux/jump_label.h>

#endif



/*

 * An instance of this structure is created in a special

 * ELF section at every dynamic debug callsite.  At runtime,
@@ -33,6 +37,12 @@ struct _ddebug { 
#define _DPRINTK_FLAGS_DEFAULT 0

#endif

	unsigned int flags:8;

#ifdef HAVE_JUMP_LABEL

	union {

		struct static_key_true dd_key_true;

		struct static_key_false dd_key_false;

	} key;

#endif

} __attribute__((aligned(8)));
@@ -60,7 +70,7 @@ void __dynamic_netdev_dbg(struct _ddebug *descriptor, 
			  const struct net_device *dev,

			  const char *fmt, ...);



#define DEFINE_DYNAMIC_DEBUG_METADATA(name, fmt)		\

#define DEFINE_DYNAMIC_DEBUG_METADATA_KEY(name, fmt, key, init)	\

	static struct _ddebug  __aligned(8)			\

	__attribute__((section("__verbose"))) name = {		\

		.modname = KBUILD_MODNAME,			\
@@ -69,12 +79,50 @@ void __dynamic_netdev_dbg(struct _ddebug *descriptor, 
		.format = (fmt),				\

		.lineno = __LINE__,				\

		.flags = _DPRINTK_FLAGS_DEFAULT,		\

		dd_key_init(key, init)				\

	}



#ifdef HAVE_JUMP_LABEL



#define dd_key_init(key, init) key = (init)



#ifdef DEBUG

#define DEFINE_DYNAMIC_DEBUG_METADATA(name, fmt) \

	DEFINE_DYNAMIC_DEBUG_METADATA_KEY(name, fmt, .key.dd_key_true, \

					  (STATIC_KEY_TRUE_INIT))



#define DYNAMIC_DEBUG_BRANCH(descriptor) \

	static_branch_likely(&descriptor.key.dd_key_true)

#else

#define DEFINE_DYNAMIC_DEBUG_METADATA(name, fmt) \

	DEFINE_DYNAMIC_DEBUG_METADATA_KEY(name, fmt, .key.dd_key_false, \

					  (STATIC_KEY_FALSE_INIT))



#define DYNAMIC_DEBUG_BRANCH(descriptor) \

	static_branch_unlikely(&descriptor.key.dd_key_false)

#endif



#else



#define dd_key_init(key, init)



#define DEFINE_DYNAMIC_DEBUG_METADATA(name, fmt) \

	DEFINE_DYNAMIC_DEBUG_METADATA_KEY(name, fmt, 0, 0)



#ifdef DEBUG

#define DYNAMIC_DEBUG_BRANCH(descriptor) \

	likely(descriptor.flags & _DPRINTK_FLAGS_PRINT)

#else

#define DYNAMIC_DEBUG_BRANCH(descriptor) \

	unlikely(descriptor.flags & _DPRINTK_FLAGS_PRINT)

#endif



#endif



#define dynamic_pr_debug(fmt, ...)				\

do {								\

	DEFINE_DYNAMIC_DEBUG_METADATA(descriptor, fmt);		\

	if (unlikely(descriptor.flags & _DPRINTK_FLAGS_PRINT))	\

	if (DYNAMIC_DEBUG_BRANCH(descriptor))			\

		__dynamic_pr_debug(&descriptor, pr_fmt(fmt),	\

				   ##__VA_ARGS__);		\

} while (0)
@@ -82,7 +130,7 @@ do { \ 
#define dynamic_dev_dbg(dev, fmt, ...)				\

do {								\

	DEFINE_DYNAMIC_DEBUG_METADATA(descriptor, fmt);		\

	if (unlikely(descriptor.flags & _DPRINTK_FLAGS_PRINT))	\

	if (DYNAMIC_DEBUG_BRANCH(descriptor))			\

		__dynamic_dev_dbg(&descriptor, dev, fmt,	\

				  ##__VA_ARGS__);		\

} while (0)
@@ -90,7 +138,7 @@ do { \ 
#define dynamic_netdev_dbg(dev, fmt, ...)			\

do {								\

	DEFINE_DYNAMIC_DEBUG_METADATA(descriptor, fmt);		\

	if (unlikely(descriptor.flags & _DPRINTK_FLAGS_PRINT))	\

	if (DYNAMIC_DEBUG_BRANCH(descriptor))			\

		__dynamic_netdev_dbg(&descriptor, dev, fmt,	\

				     ##__VA_ARGS__);		\

} while (0)
@@ -100,7 +148,7 @@ do { \ 
do {								\

	DEFINE_DYNAMIC_DEBUG_METADATA(descriptor,		\

		__builtin_constant_p(prefix_str) ? prefix_str : "hexdump");\

	if (unlikely(descriptor.flags & _DPRINTK_FLAGS_PRINT))	\

	if (DYNAMIC_DEBUG_BRANCH(descriptor))			\

		print_hex_dump(KERN_DEBUG, prefix_str,		\

			       prefix_type, rowsize, groupsize,	\

			       buf, len, ascii);		\

lib/dynamic_debug.c

+7 −0
Original line number Diff line number Diff line
@@ -188,6 +188,13 @@ static int ddebug_change(const struct ddebug_query *query, 
			newflags = (dp->flags & mask) | flags;

			if (newflags == dp->flags)

				continue;

#ifdef HAVE_JUMP_LABEL

			if (dp->flags & _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;

			vpr_info("changed %s:%d [%s]%s =%s\n",

				 trim_prefix(dp->filename), dp->lineno,

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