probes/lttng-ftrace.c

   1 /*
   2  * (C) Copyright        2009-2011 -
   3  *              Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   4  *
   5  * LTTng function tracer integration module.
   6  *
   7  * Dual LGPL v2.1/GPL v2 license.
   8  */
   9
  10 /*
  11  * Ftrace function tracer does not seem to provide synchronization between probe
  12  * teardown and callback execution. Therefore, we make this module permanently
  13  * loaded (unloadable).
  14  *
  15  * TODO: Move to register_ftrace_function() (which is exported for
  16  * modules) for Linux >= 3.0. It is faster (only enables the selected
  17  * functions), and will stay there.
  18  */
  19
  20 #include <linux/module.h>
  21 #include <linux/ftrace.h>
  22 #include <linux/slab.h>
  23 #include "../lttng-events.h"
  24 #include "../wrapper/ringbuffer/frontend_types.h"
  25 #include "../wrapper/ftrace.h"
  26 #include "../wrapper/vmalloc.h"
  27 #include "../lttng-tracer.h"
  28
  29 static
  30 void lttng_ftrace_handler(unsigned long ip, unsigned long parent_ip, void **data)
  31 {
  32         struct lttng_event *event = *data;
  33         struct lttng_channel *chan = event->chan;
  34         struct lib_ring_buffer_ctx ctx;
  35         struct {
  36                 unsigned long ip;
  37                 unsigned long parent_ip;
  38         } payload;
  39         int ret;
  40
  41         if (unlikely(!ACCESS_ONCE(chan->session->active)))
  42                 return;
  43         if (unlikely(!ACCESS_ONCE(chan->enabled)))
  44                 return;
  45         if (unlikely(!ACCESS_ONCE(event->enabled)))
  46                 return;
  47
  48         lib_ring_buffer_ctx_init(&ctx, chan->chan, event,
  49                                  sizeof(payload), lttng_alignof(payload), -1);
  50         ret = chan->ops->event_reserve(&ctx, event->id);
  51         if (ret < 0)
  52                 return;
  53         payload.ip = ip;
  54         payload.parent_ip = parent_ip;
  55         lib_ring_buffer_align_ctx(&ctx, lttng_alignof(payload));
  56         chan->ops->event_write(&ctx, &payload, sizeof(payload));
  57         chan->ops->event_commit(&ctx);
  58         return;
  59 }
  60
  61 /*
  62  * Create event description
  63  */
  64 static
  65 int lttng_create_ftrace_event(const char *name, struct lttng_event *event)
  66 {
  67         struct lttng_event_field *fields;
  68         struct lttng_event_desc *desc;
  69         int ret;
  70
  71         desc = kzalloc(sizeof(*event->desc), GFP_KERNEL);
  72         if (!desc)
  73                 return -ENOMEM;
  74         desc->name = kstrdup(name, GFP_KERNEL);
  75         if (!desc->name) {
  76                 ret = -ENOMEM;
  77                 goto error_str;
  78         }
  79         desc->nr_fields = 2;
  80         desc->fields = fields =
  81                 kzalloc(2 * sizeof(struct lttng_event_field), GFP_KERNEL);
  82         if (!desc->fields) {
  83                 ret = -ENOMEM;
  84                 goto error_fields;
  85         }
  86         fields[0].name = "ip";
  87         fields[0].type.atype = atype_integer;
  88         fields[0].type.u.basic.integer.size = sizeof(unsigned long) * CHAR_BIT;
  89         fields[0].type.u.basic.integer.alignment = lttng_alignof(unsigned long) * CHAR_BIT;
  90         fields[0].type.u.basic.integer.signedness = is_signed_type(unsigned long);
  91         fields[0].type.u.basic.integer.reverse_byte_order = 0;
  92         fields[0].type.u.basic.integer.base = 16;
  93         fields[0].type.u.basic.integer.encoding = lttng_encode_none;
  94
  95         fields[1].name = "parent_ip";
  96         fields[1].type.atype = atype_integer;
  97         fields[1].type.u.basic.integer.size = sizeof(unsigned long) * CHAR_BIT;
  98         fields[1].type.u.basic.integer.alignment = lttng_alignof(unsigned long) * CHAR_BIT;
  99         fields[1].type.u.basic.integer.signedness = is_signed_type(unsigned long);
 100         fields[1].type.u.basic.integer.reverse_byte_order = 0;
 101         fields[1].type.u.basic.integer.base = 16;
 102         fields[1].type.u.basic.integer.encoding = lttng_encode_none;
 103
 104         desc->owner = THIS_MODULE;
 105         event->desc = desc;
 106
 107         return 0;
 108
 109 error_fields:
 110         kfree(desc->name);
 111 error_str:
 112         kfree(desc);
 113         return ret;
 114 }
 115
 116 static
 117 struct ftrace_probe_ops lttng_ftrace_ops = {
 118         .func = lttng_ftrace_handler,
 119 };
 120
 121 int lttng_ftrace_register(const char *name,
 122                           const char *symbol_name,
 123                           struct lttng_event *event)
 124 {
 125         int ret;
 126
 127         ret = lttng_create_ftrace_event(name, event);
 128         if (ret)
 129                 goto error;
 130
 131         event->u.ftrace.symbol_name = kstrdup(symbol_name, GFP_KERNEL);
 132         if (!event->u.ftrace.symbol_name)
 133                 goto name_error;
 134
 135         /* Ensure the memory we just allocated don't trigger page faults */
 136         wrapper_vmalloc_sync_all();
 137
 138         ret = wrapper_register_ftrace_function_probe(event->u.ftrace.symbol_name,
 139                         &lttng_ftrace_ops, event);
 140         if (ret < 0)
 141                 goto register_error;
 142         return 0;
 143
 144 register_error:
 145         kfree(event->u.ftrace.symbol_name);
 146 name_error:
 147         kfree(event->desc->name);
 148         kfree(event->desc);
 149 error:
 150         return ret;
 151 }
 152 EXPORT_SYMBOL_GPL(lttng_ftrace_register);
 153
 154 void lttng_ftrace_unregister(struct lttng_event *event)
 155 {
 156         wrapper_unregister_ftrace_function_probe(event->u.ftrace.symbol_name,
 157                         &lttng_ftrace_ops, event);
 158 }
 159 EXPORT_SYMBOL_GPL(lttng_ftrace_unregister);
 160
 161 void lttng_ftrace_destroy_private(struct lttng_event *event)
 162 {
 163         kfree(event->u.ftrace.symbol_name);
 164         kfree(event->desc->fields);
 165         kfree(event->desc->name);
 166         kfree(event->desc);
 167 }
 168 EXPORT_SYMBOL_GPL(lttng_ftrace_destroy_private);
 169
 170 int lttng_ftrace_init(void)
 171 {
 172         wrapper_vmalloc_sync_all();
 173         return 0;
 174 }
 175 module_init(lttng_ftrace_init)
 176
 177 /*
 178  * Ftrace takes care of waiting for a grace period (RCU sched) at probe
 179  * unregistration, and disables preemption around probe call.
 180  */
 181 void lttng_ftrace_exit(void)
 182 {
 183 }
 184 module_exit(lttng_ftrace_exit)
 185
 186 MODULE_LICENSE("GPL and additional rights");
 187 MODULE_AUTHOR("Mathieu Desnoyers");
 188 MODULE_DESCRIPTION("Linux Trace Toolkit Ftrace Support");