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2fa2d39a FG |
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 | ||
64cc198b MD |
64 | #define MAX_ENTRIES 25 |
65 | ||
66 | struct lttng_cs_nesting { | |
67 | struct stack_trace stack_trace; | |
68 | unsigned long entries[MAX_ENTRIES]; | |
69 | }; | |
2fa2d39a FG |
70 | |
71 | struct lttng_cs { | |
64cc198b | 72 | struct lttng_cs_nesting level[RING_BUFFER_MAX_NESTING]; |
2fa2d39a FG |
73 | }; |
74 | ||
75 | struct field_data { | |
2fa2d39a | 76 | struct lttng_cs __percpu *cs_percpu; |
64cc198b | 77 | int mode; |
2fa2d39a FG |
78 | }; |
79 | ||
80 | struct lttng_cs_type { | |
81 | const char *name; | |
82 | const char *save_func_name; | |
83 | void (*save_func)(struct stack_trace *trace); | |
84 | }; | |
85 | ||
86 | enum lttng_cs_ctx_modes { | |
87 | CALLSTACK_KERNEL = 0, | |
88 | CALLSTACK_USER = 1, | |
89 | }; | |
90 | ||
91 | static struct lttng_cs_type cs_types[] = { | |
92 | { | |
64cc198b MD |
93 | .name = "callstack_kernel", |
94 | .save_func_name = "save_stack_trace", | |
95 | .save_func = NULL, | |
2fa2d39a FG |
96 | }, |
97 | { | |
64cc198b MD |
98 | .name = "callstack_user", |
99 | .save_func_name = "save_stack_trace_user", | |
100 | .save_func = NULL, | |
2fa2d39a FG |
101 | }, |
102 | }; | |
103 | ||
104 | static | |
105 | int init_type(int mode) | |
106 | { | |
107 | unsigned long func; | |
108 | ||
109 | if (cs_types[mode].save_func) | |
110 | return 0; | |
111 | func = kallsyms_lookup_funcptr(cs_types[mode].save_func_name); | |
112 | if (!func) { | |
113 | printk(KERN_WARNING "LTTng: symbol lookup failed: %s\n", | |
114 | cs_types[mode].save_func_name); | |
115 | return -EINVAL; | |
116 | } | |
117 | cs_types[mode].save_func = (void *) func; | |
118 | return 0; | |
119 | } | |
120 | ||
121 | static | |
122 | struct stack_trace *stack_trace_context(struct lttng_ctx_field *field, | |
123 | struct lib_ring_buffer_ctx *ctx) | |
124 | { | |
125 | int nesting; | |
126 | struct lttng_cs *cs; | |
3c1a57e8 | 127 | struct field_data *fdata = field->priv; |
2fa2d39a FG |
128 | |
129 | /* | |
130 | * get_cpu() is not required, preemption is already | |
131 | * disabled while event is written. | |
132 | * | |
133 | * max nesting is checked in lib_ring_buffer_get_cpu(). | |
134 | * Check it again as a safety net. | |
135 | */ | |
136 | cs = per_cpu_ptr(fdata->cs_percpu, ctx->cpu); | |
137 | nesting = per_cpu(lib_ring_buffer_nesting, ctx->cpu) - 1; | |
138 | if (nesting >= RING_BUFFER_MAX_NESTING) { | |
139 | return NULL; | |
140 | } | |
64cc198b | 141 | return &cs->level[nesting].stack_trace; |
2fa2d39a FG |
142 | } |
143 | ||
144 | /* | |
145 | * In order to reserve the correct size, the callstack is computed. The | |
146 | * resulting callstack is saved to be accessed in the record step. | |
147 | */ | |
148 | static | |
149 | size_t lttng_callstack_get_size(size_t offset, struct lttng_ctx_field *field, | |
150 | struct lib_ring_buffer_ctx *ctx, | |
151 | struct lttng_channel *chan) | |
152 | { | |
153 | size_t size = 0; | |
154 | struct stack_trace *trace; | |
3c1a57e8 | 155 | struct field_data *fdata = field->priv; |
2fa2d39a FG |
156 | |
157 | /* do not write data if no space is available */ | |
158 | trace = stack_trace_context(field, ctx); | |
159 | if (!trace) | |
160 | return 0; | |
161 | ||
162 | /* reset stack trace, no need to clear memory */ | |
163 | trace->nr_entries = 0; | |
164 | ||
165 | /* do the real work and reserve space */ | |
166 | cs_types[fdata->mode].save_func(trace); | |
ea15538d MD |
167 | /* |
168 | * Remove final ULONG_MAX delimiter. If we cannot find it, add | |
169 | * our own marker to show that the stack is incomplete. This is | |
170 | * more compact for a trace. | |
171 | */ | |
172 | if (trace->nr_entries > 0 | |
173 | && trace->entries[trace->nr_entries - 1] == ULONG_MAX) { | |
174 | trace->nr_entries--; | |
175 | } | |
2fa2d39a FG |
176 | size += lib_ring_buffer_align(offset, lttng_alignof(unsigned int)); |
177 | size += sizeof(unsigned int); | |
178 | size += lib_ring_buffer_align(offset, lttng_alignof(unsigned long)); | |
179 | size += sizeof(unsigned long) * trace->nr_entries; | |
ea15538d MD |
180 | /* Add our own ULONG_MAX delimiter to show incomplete stack. */ |
181 | if (trace->nr_entries == trace->max_entries) | |
182 | size += sizeof(unsigned long); | |
2fa2d39a FG |
183 | return size; |
184 | } | |
185 | ||
186 | static | |
187 | void lttng_callstack_record(struct lttng_ctx_field *field, | |
64cc198b MD |
188 | struct lib_ring_buffer_ctx *ctx, |
189 | struct lttng_channel *chan) | |
2fa2d39a FG |
190 | { |
191 | struct stack_trace *trace = stack_trace_context(field, ctx); | |
ea15538d | 192 | unsigned int nr_seq_entries; |
2fa2d39a FG |
193 | |
194 | if (!trace) | |
195 | return; | |
196 | lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned int)); | |
ea15538d MD |
197 | nr_seq_entries = trace->nr_entries; |
198 | if (trace->nr_entries == trace->max_entries) | |
199 | nr_seq_entries++; | |
200 | chan->ops->event_write(ctx, &nr_seq_entries, sizeof(unsigned int)); | |
2fa2d39a FG |
201 | lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned long)); |
202 | chan->ops->event_write(ctx, trace->entries, | |
203 | sizeof(unsigned long) * trace->nr_entries); | |
ea15538d MD |
204 | /* Add our own ULONG_MAX delimiter to show incomplete stack. */ |
205 | if (trace->nr_entries == trace->max_entries) { | |
206 | unsigned long delim = ULONG_MAX; | |
207 | ||
208 | chan->ops->event_write(ctx, &delim, sizeof(unsigned long)); | |
209 | } | |
2fa2d39a FG |
210 | } |
211 | ||
212 | static | |
213 | void field_data_free(struct field_data *fdata) | |
214 | { | |
2fa2d39a FG |
215 | if (!fdata) |
216 | return; | |
2fa2d39a FG |
217 | free_percpu(fdata->cs_percpu); |
218 | kfree(fdata); | |
219 | } | |
220 | ||
221 | static | |
64cc198b | 222 | struct field_data __percpu *field_data_create(int type) |
2fa2d39a FG |
223 | { |
224 | int cpu, i; | |
2fa2d39a | 225 | struct lttng_cs __percpu *cs_set; |
64cc198b | 226 | struct field_data *fdata; |
2fa2d39a | 227 | |
64cc198b | 228 | fdata = kzalloc(sizeof(*fdata), GFP_KERNEL); |
2fa2d39a FG |
229 | if (!fdata) |
230 | return NULL; | |
231 | cs_set = alloc_percpu(struct lttng_cs); | |
232 | if (!cs_set) | |
233 | goto error_alloc; | |
234 | ||
235 | fdata->cs_percpu = cs_set; | |
236 | for_each_possible_cpu(cpu) { | |
64cc198b MD |
237 | struct lttng_cs *cs; |
238 | ||
2fa2d39a FG |
239 | cs = per_cpu_ptr(cs_set, cpu); |
240 | for (i = 0; i < RING_BUFFER_MAX_NESTING; i++) { | |
64cc198b MD |
241 | struct lttng_cs_nesting *level; |
242 | ||
243 | level = &cs->level[i]; | |
244 | level->stack_trace.entries = level->entries; | |
245 | level->stack_trace.max_entries = MAX_ENTRIES; | |
2fa2d39a FG |
246 | } |
247 | } | |
248 | fdata->mode = type; | |
249 | return fdata; | |
250 | ||
251 | error_alloc: | |
252 | field_data_free(fdata); | |
253 | return NULL; | |
254 | } | |
255 | ||
256 | static | |
257 | void lttng_callstack_destroy(struct lttng_ctx_field *field) | |
258 | { | |
3c1a57e8 | 259 | struct field_data *fdata = field->priv; |
2fa2d39a FG |
260 | |
261 | field_data_free(fdata); | |
262 | } | |
263 | ||
264 | static | |
265 | int __lttng_add_callstack_generic(struct lttng_ctx **ctx, int mode) | |
266 | { | |
267 | const char *ctx_name = cs_types[mode].name; | |
268 | struct lttng_ctx_field *field; | |
269 | struct field_data *fdata; | |
270 | int ret; | |
271 | ||
272 | ret = init_type(mode); | |
273 | if (ret) | |
274 | return ret; | |
275 | field = lttng_append_context(ctx); | |
276 | if (!field) | |
277 | return -ENOMEM; | |
278 | if (lttng_find_context(*ctx, ctx_name)) { | |
2fa2d39a FG |
279 | ret = -EEXIST; |
280 | goto error_find; | |
281 | } | |
64cc198b | 282 | fdata = field_data_create(mode); |
2fa2d39a FG |
283 | if (!fdata) { |
284 | ret = -ENOMEM; | |
285 | goto error_create; | |
286 | } | |
287 | ||
288 | field->event_field.name = ctx_name; | |
289 | field->event_field.type.atype = atype_sequence; | |
290 | field->event_field.type.u.sequence.elem_type.atype = atype_integer; | |
291 | field->event_field.type.u.sequence.elem_type.u.basic.integer.size = sizeof(unsigned long) * CHAR_BIT; | |
292 | field->event_field.type.u.sequence.elem_type.u.basic.integer.alignment = lttng_alignof(long) * CHAR_BIT; | |
293 | field->event_field.type.u.sequence.elem_type.u.basic.integer.signedness = lttng_is_signed_type(unsigned long); | |
294 | field->event_field.type.u.sequence.elem_type.u.basic.integer.reverse_byte_order = 0; | |
295 | field->event_field.type.u.sequence.elem_type.u.basic.integer.base = 16; | |
296 | field->event_field.type.u.sequence.elem_type.u.basic.integer.encoding = lttng_encode_none; | |
297 | ||
298 | field->event_field.type.u.sequence.length_type.atype = atype_integer; | |
299 | field->event_field.type.u.sequence.length_type.u.basic.integer.size = sizeof(unsigned int) * CHAR_BIT; | |
300 | field->event_field.type.u.sequence.length_type.u.basic.integer.alignment = lttng_alignof(unsigned int) * CHAR_BIT; | |
301 | field->event_field.type.u.sequence.length_type.u.basic.integer.signedness = lttng_is_signed_type(unsigned int); | |
302 | field->event_field.type.u.sequence.length_type.u.basic.integer.reverse_byte_order = 0; | |
303 | field->event_field.type.u.sequence.length_type.u.basic.integer.base = 10; | |
304 | field->event_field.type.u.sequence.length_type.u.basic.integer.encoding = lttng_encode_none; | |
305 | ||
306 | field->get_size_arg = lttng_callstack_get_size; | |
307 | field->record = lttng_callstack_record; | |
3c1a57e8 | 308 | field->priv = fdata; |
2fa2d39a FG |
309 | field->destroy = lttng_callstack_destroy; |
310 | wrapper_vmalloc_sync_all(); | |
2fa2d39a FG |
311 | return 0; |
312 | ||
313 | error_create: | |
314 | field_data_free(fdata); | |
315 | error_find: | |
316 | lttng_remove_context_field(ctx, field); | |
317 | return ret; | |
318 | } | |
319 | ||
320 | /** | |
321 | * lttng_add_callstack_to_ctx - add callstack event context | |
322 | * | |
323 | * @ctx: the lttng_ctx pointer to initialize | |
324 | * @type: the context type | |
325 | * | |
326 | * Supported callstack type supported: | |
327 | * LTTNG_KERNEL_CONTEXT_CALLSTACK_KERNEL | |
328 | * Records the callstack of the kernel | |
329 | * LTTNG_KERNEL_CONTEXT_CALLSTACK_USER | |
330 | * Records the callstack of the userspace program (from the kernel) | |
331 | * | |
332 | * Return 0 for success, or error code. | |
333 | */ | |
334 | int lttng_add_callstack_to_ctx(struct lttng_ctx **ctx, int type) | |
335 | { | |
336 | switch (type) { | |
337 | case LTTNG_KERNEL_CONTEXT_CALLSTACK_KERNEL: | |
338 | return __lttng_add_callstack_generic(ctx, CALLSTACK_KERNEL); | |
339 | case LTTNG_KERNEL_CONTEXT_CALLSTACK_USER: | |
340 | return __lttng_add_callstack_generic(ctx, CALLSTACK_USER); | |
341 | default: | |
342 | return -EINVAL; | |
343 | } | |
344 | } | |
345 | EXPORT_SYMBOL_GPL(lttng_add_callstack_to_ctx); | |
346 | ||
347 | MODULE_LICENSE("GPL and additional rights"); | |
348 | MODULE_AUTHOR("Francis Giraldeau"); | |
349 | MODULE_DESCRIPTION("Linux Trace Toolkit Callstack Support"); |