2 * lttng-context-callstack.c
4 * LTTng callstack event context.
6 * Copyright (C) 2014 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
7 * Copyright (C) 2014 Francis Giraldeau <francis.giraldeau@gmail.com>
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.
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.
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
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.
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:
32 * size = cpus * nest * depth * sizeof(unsigned long)
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.
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.
49 * The symbol name resolution is left to the trace reader.
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"
64 #define MAX_ENTRIES 25
66 struct lttng_cs_nesting
{
67 struct stack_trace stack_trace
;
68 unsigned long entries
[MAX_ENTRIES
];
72 struct lttng_cs_nesting level
[RING_BUFFER_MAX_NESTING
];
76 struct lttng_cs __percpu
*cs_percpu
;
80 struct lttng_cs_type
{
82 const char *save_func_name
;
83 void (*save_func
)(struct stack_trace
*trace
);
86 enum lttng_cs_ctx_modes
{
91 static struct lttng_cs_type cs_types
[] = {
93 .name
= "callstack_kernel",
94 .save_func_name
= "save_stack_trace",
98 .name
= "callstack_user",
99 .save_func_name
= "save_stack_trace_user",
105 int init_type(int mode
)
109 if (cs_types
[mode
].save_func
)
111 func
= kallsyms_lookup_funcptr(cs_types
[mode
].save_func_name
);
113 printk(KERN_WARNING
"LTTng: symbol lookup failed: %s\n",
114 cs_types
[mode
].save_func_name
);
117 cs_types
[mode
].save_func
= (void *) func
;
122 struct stack_trace
*stack_trace_context(struct lttng_ctx_field
*field
,
123 struct lib_ring_buffer_ctx
*ctx
)
127 struct field_data
*fdata
= field
->priv
;
130 * get_cpu() is not required, preemption is already
131 * disabled while event is written.
133 * max nesting is checked in lib_ring_buffer_get_cpu().
134 * Check it again as a safety net.
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
) {
141 return &cs
->level
[nesting
].stack_trace
;
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.
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
)
154 struct stack_trace
*trace
;
155 struct field_data
*fdata
= field
->priv
;
157 /* do not write data if no space is available */
158 trace
= stack_trace_context(field
, ctx
);
162 /* reset stack trace, no need to clear memory */
163 trace
->nr_entries
= 0;
165 /* do the real work and reserve space */
166 cs_types
[fdata
->mode
].save_func(trace
);
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.
172 if (trace
->nr_entries
> 0
173 && trace
->entries
[trace
->nr_entries
- 1] == ULONG_MAX
) {
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
;
180 /* Add our own ULONG_MAX delimiter to show incomplete stack. */
181 if (trace
->nr_entries
== trace
->max_entries
)
182 size
+= sizeof(unsigned long);
187 void lttng_callstack_record(struct lttng_ctx_field
*field
,
188 struct lib_ring_buffer_ctx
*ctx
,
189 struct lttng_channel
*chan
)
191 struct stack_trace
*trace
= stack_trace_context(field
, ctx
);
192 unsigned int nr_seq_entries
;
196 lib_ring_buffer_align_ctx(ctx
, lttng_alignof(unsigned int));
197 nr_seq_entries
= trace
->nr_entries
;
198 if (trace
->nr_entries
== trace
->max_entries
)
200 chan
->ops
->event_write(ctx
, &nr_seq_entries
, sizeof(unsigned int));
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
);
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
;
208 chan
->ops
->event_write(ctx
, &delim
, sizeof(unsigned long));
213 void field_data_free(struct field_data
*fdata
)
217 free_percpu(fdata
->cs_percpu
);
222 struct field_data __percpu
*field_data_create(int type
)
225 struct lttng_cs __percpu
*cs_set
;
226 struct field_data
*fdata
;
228 fdata
= kzalloc(sizeof(*fdata
), GFP_KERNEL
);
231 cs_set
= alloc_percpu(struct lttng_cs
);
235 fdata
->cs_percpu
= cs_set
;
236 for_each_possible_cpu(cpu
) {
239 cs
= per_cpu_ptr(cs_set
, cpu
);
240 for (i
= 0; i
< RING_BUFFER_MAX_NESTING
; i
++) {
241 struct lttng_cs_nesting
*level
;
243 level
= &cs
->level
[i
];
244 level
->stack_trace
.entries
= level
->entries
;
245 level
->stack_trace
.max_entries
= MAX_ENTRIES
;
252 field_data_free(fdata
);
257 void lttng_callstack_destroy(struct lttng_ctx_field
*field
)
259 struct field_data
*fdata
= field
->priv
;
261 field_data_free(fdata
);
265 int __lttng_add_callstack_generic(struct lttng_ctx
**ctx
, int mode
)
267 const char *ctx_name
= cs_types
[mode
].name
;
268 struct lttng_ctx_field
*field
;
269 struct field_data
*fdata
;
272 ret
= init_type(mode
);
275 field
= lttng_append_context(ctx
);
278 if (lttng_find_context(*ctx
, ctx_name
)) {
282 fdata
= field_data_create(mode
);
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
;
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
;
306 field
->get_size_arg
= lttng_callstack_get_size
;
307 field
->record
= lttng_callstack_record
;
309 field
->destroy
= lttng_callstack_destroy
;
310 wrapper_vmalloc_sync_all();
314 field_data_free(fdata
);
316 lttng_remove_context_field(ctx
, field
);
321 * lttng_add_callstack_to_ctx - add callstack event context
323 * @ctx: the lttng_ctx pointer to initialize
324 * @type: the context type
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)
332 * Return 0 for success, or error code.
334 int lttng_add_callstack_to_ctx(struct lttng_ctx
**ctx
, int 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
);
345 EXPORT_SYMBOL_GPL(lttng_add_callstack_to_ctx
);
347 MODULE_LICENSE("GPL and additional rights");
348 MODULE_AUTHOR("Francis Giraldeau");
349 MODULE_DESCRIPTION("Linux Trace Toolkit Callstack Support");