Re: [PATCH 03/10] jump label v11: base patch

Steven Rostedt
2010-09-21T02:37:22Z

On Fri, 2010-09-17 at 11:09 -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@redhat.com>
> ---

> +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;
> + }
> + }
> + 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 */
> + 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);
> +
> +#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)

Eek!!

I'm not that strict on the 80 character limit, but the above can wrap it
twice!!!

I'll fix these extended lines myself.

-- Steve

> +{
> + 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@redhat.com>
> +
> +echo "int main(void) { entry: asm goto (\"\"::::entry); return 0; }" | $1 -x c - -c -o /dev/null >/dev/null 2>&1 && echo "y"