1 /* SPDX-License-Identifier: (GPL-2.0 or LGPL-2.1)
3 * lttng-context-callstack.c
5 * LTTng callstack event context.
7 * Copyright (C) 2014 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
8 * Copyright (C) 2014 Francis Giraldeau <francis.giraldeau@gmail.com>
10 * The callstack context can be added to any kernel event. It records
11 * either the kernel or the userspace callstack, up to a max depth. The
12 * context is a CTF sequence, such that it uses only the space required
13 * for the number of callstack entries.
15 * It allocates callstack buffers per-CPU up to 4 interrupt nesting.
16 * This nesting limit is the same as defined in the ring buffer. It
17 * therefore uses a fixed amount of memory, proportional to the number
20 * size = cpus * nest * depth * sizeof(unsigned long)
22 * Which is 4096 bytes per CPU on 64-bit host and a depth of 128.
23 * The allocation is done at the initialization to avoid memory
24 * allocation overhead while tracing, using a shallow stack.
26 * The kernel callstack is recovered using save_stack_trace(), and the
27 * userspace callstack uses save_stack_trace_user(). They rely on frame
28 * pointers. These are usually available for the kernel, but the
29 * compiler option -fomit-frame-pointer frequently used in popular Linux
30 * distributions may cause the userspace callstack to be unreliable, and
31 * is a known limitation of this approach. If frame pointers are not
32 * available, it produces no error, but the callstack will be empty. We
33 * still provide the feature, because it works well for runtime
34 * environments having frame pointers. In the future, unwind support
35 * and/or last branch record may provide a solution to this problem.
37 * The symbol name resolution is left to the trace reader.
40 #include <linux/module.h>
41 #include <linux/slab.h>
42 #include <linux/sched.h>
43 #include <linux/utsname.h>
44 #include <linux/stacktrace.h>
45 #include <linux/spinlock.h>
46 #include "lttng-events.h"
47 #include "wrapper/ringbuffer/backend.h"
48 #include "wrapper/ringbuffer/frontend.h"
49 #include "wrapper/vmalloc.h"
50 #include "lttng-tracer.h"
52 #include "lttng-context-callstack-legacy-impl.h"
55 void field_data_free(struct field_data
*fdata
)
59 free_percpu(fdata
->cs_percpu
);
64 struct field_data __percpu
*field_data_create(enum lttng_cs_ctx_modes mode
)
67 struct lttng_cs __percpu
*cs_set
;
68 struct field_data
*fdata
;
70 fdata
= kzalloc(sizeof(*fdata
), GFP_KERNEL
);
73 cs_set
= alloc_percpu(struct lttng_cs
);
77 fdata
->cs_percpu
= cs_set
;
78 for_each_possible_cpu(cpu
) {
81 cs
= per_cpu_ptr(cs_set
, cpu
);
82 for (i
= 0; i
< RING_BUFFER_MAX_NESTING
; i
++) {
83 struct lttng_cs_dispatch
*dispatch
;
85 dispatch
= &cs
->dispatch
[i
];
86 dispatch
->stack_trace
.entries
= dispatch
->entries
;
87 dispatch
->stack_trace
.max_entries
= MAX_ENTRIES
;
94 field_data_free(fdata
);
99 void lttng_callstack_destroy(struct lttng_ctx_field
*field
)
101 struct field_data
*fdata
= field
->priv
;
103 field_data_free(fdata
);
107 int __lttng_add_callstack_generic(struct lttng_ctx
**ctx
,
108 enum lttng_cs_ctx_modes mode
)
110 const char *ctx_name
= cs_types
[mode
].name
;
111 struct lttng_ctx_field
*field
;
112 struct field_data
*fdata
;
115 ret
= init_type(mode
);
118 field
= lttng_append_context(ctx
);
121 if (lttng_find_context(*ctx
, ctx_name
)) {
125 fdata
= field_data_create(mode
);
131 field
->event_field
.name
= ctx_name
;
132 field
->event_field
.type
.atype
= atype_sequence
;
133 field
->event_field
.type
.u
.sequence
.elem_type
.atype
= atype_integer
;
134 field
->event_field
.type
.u
.sequence
.elem_type
.u
.basic
.integer
.size
= sizeof(unsigned long) * CHAR_BIT
;
135 field
->event_field
.type
.u
.sequence
.elem_type
.u
.basic
.integer
.alignment
= lttng_alignof(long) * CHAR_BIT
;
136 field
->event_field
.type
.u
.sequence
.elem_type
.u
.basic
.integer
.signedness
= lttng_is_signed_type(unsigned long);
137 field
->event_field
.type
.u
.sequence
.elem_type
.u
.basic
.integer
.reverse_byte_order
= 0;
138 field
->event_field
.type
.u
.sequence
.elem_type
.u
.basic
.integer
.base
= 16;
139 field
->event_field
.type
.u
.sequence
.elem_type
.u
.basic
.integer
.encoding
= lttng_encode_none
;
141 field
->event_field
.type
.u
.sequence
.length_type
.atype
= atype_integer
;
142 field
->event_field
.type
.u
.sequence
.length_type
.u
.basic
.integer
.size
= sizeof(unsigned int) * CHAR_BIT
;
143 field
->event_field
.type
.u
.sequence
.length_type
.u
.basic
.integer
.alignment
= lttng_alignof(unsigned int) * CHAR_BIT
;
144 field
->event_field
.type
.u
.sequence
.length_type
.u
.basic
.integer
.signedness
= lttng_is_signed_type(unsigned int);
145 field
->event_field
.type
.u
.sequence
.length_type
.u
.basic
.integer
.reverse_byte_order
= 0;
146 field
->event_field
.type
.u
.sequence
.length_type
.u
.basic
.integer
.base
= 10;
147 field
->event_field
.type
.u
.sequence
.length_type
.u
.basic
.integer
.encoding
= lttng_encode_none
;
149 field
->get_size_arg
= lttng_callstack_get_size
;
150 field
->record
= lttng_callstack_record
;
152 field
->destroy
= lttng_callstack_destroy
;
153 wrapper_vmalloc_sync_all();
157 field_data_free(fdata
);
159 lttng_remove_context_field(ctx
, field
);
164 * lttng_add_callstack_to_ctx - add callstack event context
166 * @ctx: the lttng_ctx pointer to initialize
167 * @type: the context type
169 * Supported callstack type supported:
170 * LTTNG_KERNEL_CONTEXT_CALLSTACK_KERNEL
171 * Records the callstack of the kernel
172 * LTTNG_KERNEL_CONTEXT_CALLSTACK_USER
173 * Records the callstack of the userspace program (from the kernel)
175 * Return 0 for success, or error code.
177 int lttng_add_callstack_to_ctx(struct lttng_ctx
**ctx
, int type
)
180 case LTTNG_KERNEL_CONTEXT_CALLSTACK_KERNEL
:
181 return __lttng_add_callstack_generic(ctx
, CALLSTACK_KERNEL
);
183 case LTTNG_KERNEL_CONTEXT_CALLSTACK_USER
:
184 return __lttng_add_callstack_generic(ctx
, CALLSTACK_USER
);
190 EXPORT_SYMBOL_GPL(lttng_add_callstack_to_ctx
);