Date:	Tue, 21 Sep 2010 14:29:45 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Jason Baron <jbaron@...hat.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu,
	mathieu.desnoyers@...ymtl.ca, hpa@...or.com, tglx@...utronix.de,
	rostedt@...dmis.org, andi@...stfloor.org, roland@...hat.com,
	rth@...hat.com, mhiramat@...hat.com, fweisbec@...il.com,
	avi@...hat.com, davem@...emloft.net, vgoyal@...hat.com,
	sam@...nborg.org, tony@...eyournoodle.com
Subject: Re: [PATCH 03/10] jump label v11: base patch

On Fri, Sep 17, 2010 at 11:09:00AM -0400, Jason Baron wrote:
> base patch to implement 'jump labeling'. Based on a new 'asm goto' inline
> assembly gcc mechanism, we can now branch to labels from an 'asm goto'
> statment. This allows us to create a 'no-op' fastpath, which can subsequently
> be patched with a jump to the slowpath code. This is useful for code which
> might be rarely used, but which we'd like to be able to call, if needed.
> Tracepoints are the current usecase that these are being implemented for.
> 
> Signed-off-by: Jason Baron <jbaron@...hat.com>
> ---
>  Makefile                           |    5 +
>  arch/Kconfig                       |    3 +
>  arch/x86/include/asm/alternative.h |    3 +-
>  arch/x86/kernel/alternative.c      |    2 +-
>  include/asm-generic/vmlinux.lds.h  |   10 +
>  include/linux/jump_label.h         |   58 ++++++
>  include/linux/module.h             |    5 +-
>  kernel/Makefile                    |    2 +-
>  kernel/jump_label.c                |  338 ++++++++++++++++++++++++++++++++++++
>  kernel/kprobes.c                   |    1 +
>  kernel/module.c                    |    6 +
>  scripts/gcc-goto.sh                |    5 +
>  12 files changed, 434 insertions(+), 4 deletions(-)
>  create mode 100644 include/linux/jump_label.h
>  create mode 100644 kernel/jump_label.c
>  create mode 100644 scripts/gcc-goto.sh
> 
> diff --git a/Makefile b/Makefile
> index 92ab33f..a906378 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -591,6 +591,11 @@ KBUILD_CFLAGS	+= $(call cc-option,-fno-strict-overflow)
>  # conserve stack if available
>  KBUILD_CFLAGS   += $(call cc-option,-fconserve-stack)
>  
> +# check for 'asm goto'
> +ifeq ($(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-goto.sh $(CC)), y)
> +	KBUILD_CFLAGS += -DCC_HAVE_ASM_GOTO
> +endif
> +
>  # Add user supplied CPPFLAGS, AFLAGS and CFLAGS as the last assignments
>  # But warn user when we do so
>  warn-assign = \
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 4877a8c..1462d84 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -158,4 +158,7 @@ config HAVE_PERF_EVENTS_NMI
>  	  subsystem.  Also has support for calculating CPU cycle events
>  	  to determine how many clock cycles in a given period.
>  
> +config HAVE_ARCH_JUMP_LABEL
> +	bool
> +
>  source "kernel/gcov/Kconfig"
> diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
> index 634bf78..76561d2 100644
> --- a/arch/x86/include/asm/alternative.h
> +++ b/arch/x86/include/asm/alternative.h
> @@ -4,6 +4,7 @@
>  #include <linux/types.h>
>  #include <linux/stddef.h>
>  #include <linux/stringify.h>
> +#include <linux/jump_label.h>
>  #include <asm/asm.h>
>  
>  /*
> @@ -182,7 +183,7 @@ extern void *text_poke_early(void *addr, const void *opcode, size_t len);
>  extern void *text_poke(void *addr, const void *opcode, size_t len);
>  extern void *text_poke_smp(void *addr, const void *opcode, size_t len);
>  
> -#if defined(CONFIG_DYNAMIC_FTRACE)
> +#if defined(CONFIG_DYNAMIC_FTRACE) || defined(HAVE_JUMP_LABEL)
>  #define IDEAL_NOP_SIZE_5 5
>  extern unsigned char ideal_nop5[IDEAL_NOP_SIZE_5];
>  extern void arch_init_ideal_nop5(void);
> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> index 083bd01..cb0e6d3 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -641,7 +641,7 @@ void *__kprobes text_poke_smp(void *addr, const void *opcode, size_t len)
>  	return addr;
>  }
>  
> -#if defined(CONFIG_DYNAMIC_FTRACE)
> +#if defined(CONFIG_DYNAMIC_FTRACE) || defined(HAVE_JUMP_LABEL)
>  
>  unsigned char ideal_nop5[IDEAL_NOP_SIZE_5];
>  
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index 8a92a17..ef2af99 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -220,6 +220,8 @@
>  									\
>  	BUG_TABLE							\
>  									\
> +	JUMP_TABLE							\
> +									\
>  	/* PCI quirks */						\
>  	.pci_fixup        : AT(ADDR(.pci_fixup) - LOAD_OFFSET) {	\
>  		VMLINUX_SYMBOL(__start_pci_fixups_early) = .;		\
> @@ -563,6 +565,14 @@
>  #define BUG_TABLE
>  #endif
>  
> +#define JUMP_TABLE							\
> +	. = ALIGN(8);							\
> +	__jump_table : AT(ADDR(__jump_table) - LOAD_OFFSET) {		\
> +		VMLINUX_SYMBOL(__start___jump_table) = .;		\
> +		*(__jump_table)						\
> +		VMLINUX_SYMBOL(__stop___jump_table) = .;		\
> +	}
> +
>  #ifdef CONFIG_PM_TRACE
>  #define TRACEDATA							\
>  	. = ALIGN(4);							\
> diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
> new file mode 100644
> index 0000000..de58656
> --- /dev/null
> +++ b/include/linux/jump_label.h
> @@ -0,0 +1,58 @@
> +#ifndef _LINUX_JUMP_LABEL_H
> +#define _LINUX_JUMP_LABEL_H
> +
> +#if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_HAVE_ARCH_JUMP_LABEL)
> +# include <asm/jump_label.h>
> +# define HAVE_JUMP_LABEL
> +#endif
> +
> +enum jump_label_type {
> +	JUMP_LABEL_ENABLE,
> +	JUMP_LABEL_DISABLE
> +};
> +
> +struct module;
> +
> +#ifdef HAVE_JUMP_LABEL
> +
> +extern struct jump_entry __start___jump_table[];
> +extern struct jump_entry __stop___jump_table[];
> +
> +extern void arch_jump_label_transform(struct jump_entry *entry,
> +				 enum jump_label_type type);
> +extern void jump_label_update(unsigned long key, enum jump_label_type type);
> +extern void jump_label_apply_nops(struct module *mod);
> +extern void arch_jump_label_text_poke_early(jump_label_t addr);
> +
> +#define enable_jump_label(key) \
> +	jump_label_update((unsigned long)key, JUMP_LABEL_ENABLE);
> +
> +#define disable_jump_label(key) \
> +	jump_label_update((unsigned long)key, JUMP_LABEL_DISABLE);
> +
> +#else
> +
> +#define JUMP_LABEL(key, label)			\
> +do {						\
> +	if (unlikely(*key))			\
> +		goto label;			\
> +} while (0)
> +
> +#define enable_jump_label(cond_var)	\
> +do {					\
> +       *(cond_var) = 1;			\
> +} while (0)
> +
> +#define disable_jump_label(cond_var)	\
> +do {					\
> +       *(cond_var) = 0;			\
> +} while (0)
> +
> +static inline int jump_label_apply_nops(struct module *mod)
> +{
> +	return 0;
> +}
> +
> +#endif
> +
> +#endif
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 8a6b9fd..403ac26 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -350,7 +350,10 @@ struct module
>  	struct tracepoint *tracepoints;
>  	unsigned int num_tracepoints;
>  #endif
> -
> +#ifdef HAVE_JUMP_LABEL
> +	struct jump_entry *jump_entries;
> +	unsigned int num_jump_entries;
> +#endif
>  #ifdef CONFIG_TRACING
>  	const char **trace_bprintk_fmt_start;
>  	unsigned int num_trace_bprintk_fmt;
> diff --git a/kernel/Makefile b/kernel/Makefile
> index 92b7420..8a0feb7 100644
> --- a/kernel/Makefile
> +++ b/kernel/Makefile
> @@ -10,7 +10,7 @@ obj-y     = sched.o fork.o exec_domain.o panic.o printk.o \
>  	    kthread.o wait.o kfifo.o sys_ni.o posix-cpu-timers.o mutex.o \
>  	    hrtimer.o rwsem.o nsproxy.o srcu.o semaphore.o \
>  	    notifier.o ksysfs.o pm_qos_params.o sched_clock.o cred.o \
> -	    async.o range.o
> +	    async.o range.o jump_label.o
>  obj-y += groups.o
>  
>  ifdef CONFIG_FUNCTION_TRACER
> diff --git a/kernel/jump_label.c b/kernel/jump_label.c
> new file mode 100644
> index 0000000..07656ec
> --- /dev/null
> +++ b/kernel/jump_label.c
> @@ -0,0 +1,338 @@
> +/*
> + * jump label support
> + *
> + * Copyright (C) 2009 Jason Baron <jbaron@...hat.com>

Wrong year.
> + *
> + */
> +#include <linux/jump_label.h>
> +#include <linux/memory.h>
> +#include <linux/uaccess.h>
> +#include <linux/module.h>
> +#include <linux/list.h>
> +#include <linux/jhash.h>
> +#include <linux/slab.h>
> +#include <linux/sort.h>
> +#include <linux/err.h>
> +
> +#ifdef HAVE_JUMP_LABEL
> +
> +#define JUMP_LABEL_HASH_BITS 6
> +#define JUMP_LABEL_TABLE_SIZE (1 << JUMP_LABEL_HASH_BITS)
> +static struct hlist_head jump_label_table[JUMP_LABEL_TABLE_SIZE];
> +
> +/* mutex to protect coming/going of the the jump_label table */
> +static DEFINE_MUTEX(jump_label_mutex);
> +
> +struct jump_label_entry {
> +	struct hlist_node hlist;
> +	struct jump_entry *table;
> +	int nr_entries;
> +	/* hang modules off here */
> +	struct hlist_head modules;
> +	unsigned long key;
> +};
> +
> +struct jump_label_module_entry {
> +	struct hlist_node hlist;
> +	struct jump_entry *table;
> +	int nr_entries;
> +	struct module *mod;
> +};
> +
> +static int jump_label_cmp(const void *a, const void *b)
> +{
> +	const struct jump_entry *jea = a;
> +	const struct jump_entry *jeb = b;
> +
> +	if (jea->key < jeb->key)
> +		return -1;
> +
> +	if (jea->key > jeb->key)
> +		return 1;
> +
> +	return 0;
> +}
> +
> +static void sort_jump_label_entries(struct jump_entry *start, struct jump_entry *stop)
> +{
> +	unsigned long size;
> +
> +	size = (((unsigned long)stop - (unsigned long)start)
> +					/ sizeof(struct jump_entry));
> +	sort(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL);
> +}
> +
> +static struct jump_label_entry *get_jump_label_entry(jump_label_t key)
> +{
> +	struct hlist_head *head;
> +	struct hlist_node *node;
> +	struct jump_label_entry *e;
> +	u32 hash = jhash((void *)&key, sizeof(jump_label_t), 0);
> +
> +	head = &jump_label_table[hash & (JUMP_LABEL_TABLE_SIZE - 1)];
> +	hlist_for_each_entry(e, node, head, hlist) {
> +		if (key == e->key)
> +			return e;
> +	}
> +	return NULL;
> +}
> +
> +static struct jump_label_entry *add_jump_label_entry(jump_label_t key, int nr_entries, struct jump_entry *table)
> +{
> +	struct hlist_head *head;
> +	struct jump_label_entry *e;
> +	u32 hash;
> +
> +	e = get_jump_label_entry(key);
> +	if (e)
> +		return ERR_PTR(-EEXIST);
> +
> +	e = kmalloc(sizeof(struct jump_label_entry), GFP_KERNEL);
> +	if (!e)
> +		return ERR_PTR(-ENOMEM);
> +
> +	hash = jhash((void *)&key, sizeof(jump_label_t), 0);
> +	head = &jump_label_table[hash & (JUMP_LABEL_TABLE_SIZE - 1)];
> +	e->key = key;
> +	e->table = table;
> +	e->nr_entries = nr_entries;
> +	INIT_HLIST_HEAD(&(e->modules));
> +	hlist_add_head(&e->hlist, head);
> +	return e;
> +}
> +
> +static int build_jump_label_hashtable(struct jump_entry *start, struct jump_entry *stop)
> +{
> +	struct jump_entry *iter, *iter_begin;
> +	struct jump_label_entry *entry;
> +	int count;
> +
> +	sort_jump_label_entries(start, stop);
> +	iter = start;
> +	while (iter < stop) {
> +		entry = get_jump_label_entry(iter->key);
> +		if (!entry) {
> +			iter_begin = iter;
> +			count = 0;
> +			while ((iter < stop) &&
> +				(iter->key == iter_begin->key)) {
> +				iter++;
> +				count++;
> +			}
> +			entry = add_jump_label_entry(iter_begin->key,
> +							count, iter_begin);
> +			if (IS_ERR(entry))
> +				return PTR_ERR(entry);
> +		 } else {
> +			WARN_ONCE(1, KERN_ERR "build_jump_hashtable: unexpected entry!\n");
> +			return -1;

Would it make sense to use a different value? Say -EINVAL?
> +		}
> +	}
> +	return 0;
> +}
> +
> +/***
> + * jump_label_update - update jump label text
> + * @key -  key value associated with a a jump label
> + * @type - enum set to JUMP_LABEL_ENABLE or JUMP_LABEL_DISABLE
> + *
> + * Will enable/disable the jump for jump label @key, depending on the
> + * value of @type.
> + *
> + */
> +
> +void jump_label_update(unsigned long key, enum jump_label_type type)
> +{
> +	struct jump_entry *iter;
> +	struct jump_label_entry *entry;
> +	struct hlist_node *module_node;
> +	struct jump_label_module_entry *e_module;
> +	int count;
> +
> +	mutex_lock(&jump_label_mutex);
> +	entry = get_jump_label_entry((jump_label_t)key);
> +	if (entry) {
> +		count = entry->nr_entries;
> +		iter = entry->table;
> +		while (count--) {
> +			if (kernel_text_address(iter->code))
> +				arch_jump_label_transform(iter, type);
> +			iter++;
> +		}
> +		/* eanble/disable jump labels in modules */

"enable"

> +		hlist_for_each_entry(e_module, module_node, &(entry->modules),
> +							hlist) {
> +			count = e_module->nr_entries;
> +			iter = e_module->table;
> +			while (count--) {
> +				if (kernel_text_address(iter->code))
> +					arch_jump_label_transform(iter, type);
> +				iter++;
> +			}
> +		}
> +	}
> +	mutex_unlock(&jump_label_mutex);
> +}
> +
> +static __init int init_jump_label(void)
> +{
> +	int ret;
> +	struct jump_entry *iter_start = __start___jump_table;
> +	struct jump_entry *iter_stop = __stop___jump_table;
> +	struct jump_entry *iter;
> +
> +	mutex_lock(&jump_label_mutex);
> +	ret = build_jump_label_hashtable(__start___jump_table,
> +					 __stop___jump_table);
> +	iter = iter_start;
> +	while (iter < iter_stop) {
> +		arch_jump_label_text_poke_early(iter->code);
> +		iter++;
> +	}
> +	mutex_unlock(&jump_label_mutex);
> +	return ret;
> +}
> +early_initcall(init_jump_label);

Is there any danger of not patching the instructions with NOPs before
early_initcall is called? I guess for your uses (tracing) there won't.
And even if there are not patched it will just call the function.

> +
> +#ifdef CONFIG_MODULES
> +
> +static struct jump_label_module_entry *add_jump_label_module_entry(struct jump_label_entry *entry, struct jump_entry *iter_begin, int count, struct module *mod)
> +{
> +	struct jump_label_module_entry *e;
> +
> +	e = kmalloc(sizeof(struct jump_label_module_entry), GFP_KERNEL);
> +	if (!e)
> +		return ERR_PTR(-ENOMEM);
> +	e->mod = mod;
> +	e->nr_entries = count;
> +	e->table = iter_begin;
> +	hlist_add_head(&e->hlist, &entry->modules);
> +	return e;
> +}
> +
> +static int add_jump_label_module(struct module *mod)
> +{
> +	struct jump_entry *iter, *iter_begin;
> +	struct jump_label_entry *entry;
> +	struct jump_label_module_entry *module_entry;
> +	int count;
> +
> +	/* if the module doesn't have jump label entries, just return */
> +	if (!mod->num_jump_entries)
> +		return 0;
> +
> +	sort_jump_label_entries(mod->jump_entries,
> +				mod->jump_entries + mod->num_jump_entries);
> +	iter = mod->jump_entries;
> +	while (iter < mod->jump_entries + mod->num_jump_entries) {
> +		entry = get_jump_label_entry(iter->key);
> +		iter_begin = iter;
> +		count = 0;
> +		while ((iter < mod->jump_entries + mod->num_jump_entries) &&
> +			(iter->key == iter_begin->key)) {
> +				iter++;
> +				count++;
> +		}
> +		if (!entry) {
> +			entry = add_jump_label_entry(iter_begin->key, 0, NULL);
> +			if (IS_ERR(entry))
> +				return PTR_ERR(entry);
> +		}
> +		module_entry = add_jump_label_module_entry(entry, iter_begin,
> +							   count, mod);
> +		if (IS_ERR(module_entry))
> +			return PTR_ERR(module_entry);
> +	}
> +	return 0;
> +}
> +
> +static void remove_jump_label_module(struct module *mod)
> +{
> +	struct hlist_head *head;
> +	struct hlist_node *node, *node_next, *module_node, *module_node_next;
> +	struct jump_label_entry *e;
> +	struct jump_label_module_entry *e_module;
> +	int i;
> +
> +	/* if the module doesn't have jump label entries, just return */
> +	if (!mod->num_jump_entries)
> +		return;
> +
> +	for (i = 0; i < JUMP_LABEL_TABLE_SIZE; i++) {
> +		head = &jump_label_table[i];
> +		hlist_for_each_entry_safe(e, node, node_next, head, hlist) {
> +			hlist_for_each_entry_safe(e_module, module_node,
> +						  module_node_next,
> +						  &(e->modules), hlist) {
> +				if (e_module->mod == mod) {
> +					hlist_del(&e_module->hlist);
> +					kfree(e_module);
> +				}
> +			}
> +			if (hlist_empty(&e->modules) && (e->nr_entries == 0)) {
> +				hlist_del(&e->hlist);
> +				kfree(e);
> +			}
> +		}
> +	}
> +}
> +
> +static int jump_label_module_notify(struct notifier_block *self, unsigned long val, void *data)
> +{
> +	struct module *mod = data;
> +	int ret = 0;
> +
> +	switch (val) {
> +	case MODULE_STATE_COMING:
> +		mutex_lock(&jump_label_mutex);
> +		ret = add_jump_label_module(mod);
> +		if (ret)
> +			remove_jump_label_module(mod);
> +		mutex_unlock(&jump_label_mutex);
> +		break;
> +	case MODULE_STATE_GOING:
> +		mutex_lock(&jump_label_mutex);
> +		remove_jump_label_module(mod);
> +		mutex_unlock(&jump_label_mutex);
> +		break;
> +	}
> +	return ret;
> +}
> +
> +/***
> + * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
> + * @mod: module to patch
> + *
> + * Allow for run-time selection of the optimal nops. Before the module
> + * loads patch these with arch_get_jump_label_nop(), which is specified by
> + * the arch specific jump label code.
> + */
> +void jump_label_apply_nops(struct module *mod)
> +{
> +	struct jump_entry *iter;
> +
> +	/* if the module doesn't have jump label entries, just return */
> +	if (!mod->num_jump_entries)
> +		return;
> +
> +	iter = mod->jump_entries;
> +	while (iter < mod->jump_entries + mod->num_jump_entries) {
> +		arch_jump_label_text_poke_early(iter->code);
> +		iter++;
> +	}
> +}
> +
> +struct notifier_block jump_label_module_nb = {
> +	.notifier_call = jump_label_module_notify,
> +	.priority = 0,
> +};
> +
> +static __init int init_jump_label_module(void)
> +{
> +	return register_module_notifier(&jump_label_module_nb);
> +}
> +early_initcall(init_jump_label_module);
> +
> +#endif /* CONFIG_MODULES */
> +
> +#endif
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 282035f..798adfa 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -47,6 +47,7 @@
>  #include <linux/memory.h>
>  #include <linux/ftrace.h>
>  #include <linux/cpu.h>
> +#include <linux/jump_label.h>
>  
>  #include <asm-generic/sections.h>
>  #include <asm/cacheflush.h>
> diff --git a/kernel/module.c b/kernel/module.c
> index d0b5f8d..eba1341 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -55,6 +55,7 @@
>  #include <linux/async.h>
>  #include <linux/percpu.h>
>  #include <linux/kmemleak.h>
> +#include <linux/jump_label.h>
>  
>  #define CREATE_TRACE_POINTS
>  #include <trace/events/module.h>
> @@ -2308,6 +2309,11 @@ static void find_module_sections(struct module *mod, struct load_info *info)
>  					sizeof(*mod->tracepoints),
>  					&mod->num_tracepoints);
>  #endif
> +#ifdef HAVE_JUMP_LABEL
> +	mod->jump_entries = section_objs(info, "__jump_table",
> +					sizeof(*mod->jump_entries),
> +					&mod->num_jump_entries);
> +#endif
>  #ifdef CONFIG_EVENT_TRACING
>  	mod->trace_events = section_objs(info, "_ftrace_events",
>  					 sizeof(*mod->trace_events),
> diff --git a/scripts/gcc-goto.sh b/scripts/gcc-goto.sh
> new file mode 100644
> index 0000000..8e82424
> --- /dev/null
> +++ b/scripts/gcc-goto.sh
> @@ -0,0 +1,5 @@
> +#!/bin/sh
> +# Test for gcc 'asm goto' suport
> +# Copyright (C) 2010, Jason Baron <jbaron@...hat.com>
> +
> +echo "int main(void) { entry: asm goto (\"\"::::entry); return 0; }" | $1 -x c - -c -o /dev/null >/dev/null 2>&1 && echo "y"
> -- 
> 1.7.1
> 
> --
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