lttng-context-callstack.c

   1 /*
   2  * lttng-context-callstack.c
   3  *
   4  * LTTng callstack event context.
   5  *
   6  * Copyright (C) 2014 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   7  * Copyright (C) 2014 Francis Giraldeau <francis.giraldeau@gmail.com>
   8  *
   9  * This library is free software; you can redistribute it and/or
  10  * modify it under the terms of the GNU Lesser General Public
  11  * License as published by the Free Software Foundation; only
  12  * version 2.1 of the License.
  13  *
  14  * This library is distributed in the hope that it will be useful,
  15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  17  * Lesser General Public License for more details.
  18  *
  19  * You should have received a copy of the GNU Lesser General Public
  20  * License along with this library; if not, write to the Free Software
  21  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  22  *
  23  * The callstack context can be added to any kernel
  24  * event. It records either the kernel or the userspace callstack, up to a
  25  * max depth. The context is a CTF sequence, such that it uses only the space
  26  * required for the number of callstack entries.
  27  *
  28  * It allocates callstack buffers per-CPU up to 4 interrupt nesting. This
  29  * nesting limit is the same as defined in the ring buffer. It therefore uses a
  30  * fixed amount of memory, proportional to the number of CPUs:
  31  *
  32  *   size = cpus * nest * depth * sizeof(unsigned long)
  33  *
  34  * Which is about 800 bytes per-CPUs on 64-bit host and a depth of 25. The
  35  * allocation is done at the initialization to avoid memory allocation
  36  * overhead while tracing, using a shallow stack.
  37  *
  38  * The kernel callstack is recovered using save_stack_trace(), and the
  39  * userspace callstack uses save_stack_trace_user(). They rely on frame
  40  * pointers. These are usually available for the kernel, but the compiler
  41  * option -fomit-frame-pointer frequently used in popular Linux distributions
  42  * may cause the userspace callstack to be unreliable, and is a known
  43  * limitation of this approach. If frame pointers are not available, it
  44  * produces no error, but the callstack will be empty. We still provide the
  45  * feature, because it works well for runtime environments having frame
  46  * pointers. In the future, unwind support and/or last branch record may
  47  * provide a solution to this problem.
  48  *
  49  * The symbol name resolution is left to the trace reader.
  50  */
  51
  52 #include <linux/module.h>
  53 #include <linux/slab.h>
  54 #include <linux/sched.h>
  55 #include <linux/utsname.h>
  56 #include <linux/stacktrace.h>
  57 #include <linux/spinlock.h>
  58 #include "lttng-events.h"
  59 #include "wrapper/ringbuffer/backend.h"
  60 #include "wrapper/ringbuffer/frontend.h"
  61 #include "wrapper/vmalloc.h"
  62 #include "lttng-tracer.h"
  63
  64 #define MAX_ENTRIES 25 /* BUG: saving more than 30 entries causes trace corruption */
  65
  66 struct lttng_cs {
  67         struct stack_trace items[RING_BUFFER_MAX_NESTING];
  68 };
  69
  70 struct field_data {
  71         int mode;
  72         struct lttng_cs __percpu *cs_percpu;
  73 };
  74
  75 struct lttng_cs_type {
  76         const char *name;
  77         const char *save_func_name;
  78         void (*save_func)(struct stack_trace *trace);
  79 };
  80
  81 enum lttng_cs_ctx_modes {
  82         CALLSTACK_KERNEL = 0,
  83         CALLSTACK_USER = 1,
  84 };
  85
  86 static struct lttng_cs_type cs_types[] = {
  87         {
  88           .name           = "callstack_kernel",
  89           .save_func_name = "save_stack_trace",
  90           .save_func      = NULL,
  91         },
  92         {
  93           .name           = "callstack_user",
  94           .save_func_name = "save_stack_trace_user",
  95           .save_func      = NULL,
  96         },
  97 };
  98
  99 static
 100 int init_type(int mode)
 101 {
 102         unsigned long func;
 103
 104         if (cs_types[mode].save_func)
 105                 return 0;
 106         func = kallsyms_lookup_funcptr(cs_types[mode].save_func_name);
 107         if (!func) {
 108                 printk(KERN_WARNING "LTTng: symbol lookup failed: %s\n",
 109                                 cs_types[mode].save_func_name);
 110                 return -EINVAL;
 111         }
 112         cs_types[mode].save_func = (void *) func;
 113         return 0;
 114 }
 115
 116 static
 117 struct stack_trace *stack_trace_context(struct lttng_ctx_field *field,
 118                                         struct lib_ring_buffer_ctx *ctx)
 119 {
 120         int nesting;
 121         struct lttng_cs *cs;
 122         struct field_data *fdata = field->private;
 123
 124         /*
 125          * get_cpu() is not required, preemption is already
 126          * disabled while event is written.
 127          *
 128          * max nesting is checked in lib_ring_buffer_get_cpu().
 129          * Check it again as a safety net.
 130          */
 131         cs = per_cpu_ptr(fdata->cs_percpu, ctx->cpu);
 132         nesting = per_cpu(lib_ring_buffer_nesting, ctx->cpu) - 1;
 133         if (nesting >= RING_BUFFER_MAX_NESTING) {
 134                 return NULL;
 135         }
 136         return &cs->items[nesting];
 137 }
 138
 139 /*
 140  * In order to reserve the correct size, the callstack is computed. The
 141  * resulting callstack is saved to be accessed in the record step.
 142  */
 143 static
 144 size_t lttng_callstack_get_size(size_t offset, struct lttng_ctx_field *field,
 145                                 struct lib_ring_buffer_ctx *ctx,
 146                                 struct lttng_channel *chan)
 147 {
 148         size_t size = 0;
 149         struct stack_trace *trace;
 150         struct field_data *fdata = field->private;
 151
 152         /* do not write data if no space is available */
 153         trace = stack_trace_context(field, ctx);
 154         if (!trace)
 155                 return 0;
 156
 157         /* reset stack trace, no need to clear memory */
 158         trace->nr_entries = 0;
 159
 160         /* do the real work and reserve space */
 161         cs_types[fdata->mode].save_func(trace);
 162         size += lib_ring_buffer_align(offset, lttng_alignof(unsigned int));
 163         size += sizeof(unsigned int);
 164         size += lib_ring_buffer_align(offset, lttng_alignof(unsigned long));
 165         size += sizeof(unsigned long) * trace->nr_entries;
 166         return size;
 167 }
 168
 169 static
 170 void lttng_callstack_record(struct lttng_ctx_field *field,
 171                             struct lib_ring_buffer_ctx *ctx,
 172                             struct lttng_channel *chan)
 173 {
 174         struct stack_trace *trace = stack_trace_context(field, ctx);
 175
 176         if (!trace)
 177                 return;
 178         lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned int));
 179         chan->ops->event_write(ctx, &trace->nr_entries, sizeof(unsigned int));
 180         lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned long));
 181         chan->ops->event_write(ctx, trace->entries,
 182                         sizeof(unsigned long) * trace->nr_entries);
 183 }
 184
 185 static
 186 void field_data_free(struct field_data *fdata)
 187 {
 188         int cpu, i;
 189         struct lttng_cs *cs;
 190
 191         if (!fdata)
 192                 return;
 193         for_each_possible_cpu(cpu) {
 194                 cs = per_cpu_ptr(fdata->cs_percpu, cpu);
 195                 for (i = 0; i < RING_BUFFER_MAX_NESTING; i++) {
 196                         kfree(cs->items[i].entries);
 197                 }
 198         }
 199         free_percpu(fdata->cs_percpu);
 200         kfree(fdata);
 201 }
 202
 203 static
 204 struct field_data __percpu *field_data_create(unsigned int entries, int type)
 205 {
 206         int cpu, i;
 207         struct stack_trace *item;
 208         struct lttng_cs *cs;
 209         struct lttng_cs __percpu *cs_set;
 210         struct field_data* fdata;
 211
 212         fdata = kzalloc(sizeof(unsigned long) * entries, GFP_KERNEL);
 213         if (!fdata)
 214                 return NULL;
 215         cs_set = alloc_percpu(struct lttng_cs);
 216         if (!cs_set)
 217                 goto error_alloc;
 218
 219         fdata->cs_percpu = cs_set;
 220         for_each_possible_cpu(cpu) {
 221                 cs = per_cpu_ptr(cs_set, cpu);
 222                 for (i = 0; i < RING_BUFFER_MAX_NESTING; i++) {
 223                         item = &cs->items[i];
 224                         item->entries = kzalloc(sizeof(unsigned long) * entries, GFP_KERNEL);
 225                         if (!item->entries) {
 226                                 goto error_alloc;
 227                         }
 228                         item->max_entries = entries;
 229                 }
 230         }
 231         fdata->mode = type;
 232         return fdata;
 233
 234 error_alloc:
 235         field_data_free(fdata);
 236         return NULL;
 237 }
 238
 239 static
 240 void lttng_callstack_destroy(struct lttng_ctx_field *field)
 241 {
 242         struct field_data *fdata = field->private;
 243
 244         field_data_free(fdata);
 245 }
 246
 247 static
 248 int __lttng_add_callstack_generic(struct lttng_ctx **ctx, int mode)
 249 {
 250         const char *ctx_name = cs_types[mode].name;
 251         struct lttng_ctx_field *field;
 252         struct field_data *fdata;
 253         int ret;
 254
 255         ret = init_type(mode);
 256         if (ret)
 257                 return ret;
 258         field = lttng_append_context(ctx);
 259         if (!field)
 260                 return -ENOMEM;
 261         if (lttng_find_context(*ctx, ctx_name)) {
 262                 printk("%s lttng_find_context failed\n", ctx_name);
 263                 ret = -EEXIST;
 264                 goto error_find;
 265         }
 266         fdata = field_data_create(MAX_ENTRIES, mode);
 267         if (!fdata) {
 268                 ret = -ENOMEM;
 269                 goto error_create;
 270         }
 271
 272         field->event_field.name = ctx_name;
 273         field->event_field.type.atype = atype_sequence;
 274         field->event_field.type.u.sequence.elem_type.atype = atype_integer;
 275         field->event_field.type.u.sequence.elem_type.u.basic.integer.size = sizeof(unsigned long) * CHAR_BIT;
 276         field->event_field.type.u.sequence.elem_type.u.basic.integer.alignment = lttng_alignof(long) * CHAR_BIT;
 277         field->event_field.type.u.sequence.elem_type.u.basic.integer.signedness = lttng_is_signed_type(unsigned long);
 278         field->event_field.type.u.sequence.elem_type.u.basic.integer.reverse_byte_order = 0;
 279         field->event_field.type.u.sequence.elem_type.u.basic.integer.base = 16;
 280         field->event_field.type.u.sequence.elem_type.u.basic.integer.encoding = lttng_encode_none;
 281
 282         field->event_field.type.u.sequence.length_type.atype = atype_integer;
 283         field->event_field.type.u.sequence.length_type.u.basic.integer.size = sizeof(unsigned int) * CHAR_BIT;
 284         field->event_field.type.u.sequence.length_type.u.basic.integer.alignment = lttng_alignof(unsigned int) * CHAR_BIT;
 285         field->event_field.type.u.sequence.length_type.u.basic.integer.signedness = lttng_is_signed_type(unsigned int);
 286         field->event_field.type.u.sequence.length_type.u.basic.integer.reverse_byte_order = 0;
 287         field->event_field.type.u.sequence.length_type.u.basic.integer.base = 10;
 288         field->event_field.type.u.sequence.length_type.u.basic.integer.encoding = lttng_encode_none;
 289
 290         field->get_size_arg = lttng_callstack_get_size;
 291         field->record = lttng_callstack_record;
 292         field->private = fdata;
 293         field->destroy = lttng_callstack_destroy;
 294         wrapper_vmalloc_sync_all();
 295         printk("lttng add-context %s\n", ctx_name);
 296         return 0;
 297
 298 error_create:
 299         field_data_free(fdata);
 300 error_find:
 301         lttng_remove_context_field(ctx, field);
 302         return ret;
 303 }
 304
 305 /**
 306  *      lttng_add_callstack_to_ctx - add callstack event context
 307  *
 308  *      @ctx: the lttng_ctx pointer to initialize
 309  *      @type: the context type
 310  *
 311  *      Supported callstack type supported:
 312  *      LTTNG_KERNEL_CONTEXT_CALLSTACK_KERNEL
 313  *              Records the callstack of the kernel
 314  *      LTTNG_KERNEL_CONTEXT_CALLSTACK_USER
 315  *              Records the callstack of the userspace program (from the kernel)
 316  *
 317  * Return 0 for success, or error code.
 318  */
 319 int lttng_add_callstack_to_ctx(struct lttng_ctx **ctx, int type)
 320 {
 321         switch (type) {
 322         case LTTNG_KERNEL_CONTEXT_CALLSTACK_KERNEL:
 323                 return __lttng_add_callstack_generic(ctx, CALLSTACK_KERNEL);
 324         case LTTNG_KERNEL_CONTEXT_CALLSTACK_USER:
 325                 return __lttng_add_callstack_generic(ctx, CALLSTACK_USER);
 326         default:
 327                 return -EINVAL;
 328         }
 329 }
 330 EXPORT_SYMBOL_GPL(lttng_add_callstack_to_ctx);
 331
 332 MODULE_LICENSE("GPL and additional rights");
 333 MODULE_AUTHOR("Francis Giraldeau");
 334 MODULE_DESCRIPTION("Linux Trace Toolkit Callstack Support");