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1 | /* SPDX-License-Identifier: (GPL-2.0 or LGPL-2.1) |
2 | * | |
3 | * lttng-context-callstack-stackwalk-impl.h | |
4 | * | |
5 | * LTTng callstack event context, stackwalk implementation. Targets | |
6 | * kernels and architectures using the stacktrace common infrastructure | |
7 | * introduced in the upstream Linux kernel by commit 214d8ca6ee | |
8 | * "stacktrace: Provide common infrastructure" (merged in Linux 5.2, | |
9 | * then gradually introduced within architectures). | |
10 | * | |
11 | * Copyright (C) 2014-2019 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> | |
12 | * Copyright (C) 2014 Francis Giraldeau <francis.giraldeau@gmail.com> | |
13 | */ | |
14 | ||
15 | #define MAX_ENTRIES 128 | |
16 | ||
17 | enum lttng_cs_ctx_modes { | |
18 | CALLSTACK_KERNEL = 0, | |
19 | CALLSTACK_USER = 1, | |
20 | NR_CALLSTACK_MODES, | |
21 | }; | |
22 | ||
23 | struct lttng_stack_trace { | |
24 | unsigned long entries[MAX_ENTRIES]; | |
25 | unsigned int nr_entries; | |
26 | }; | |
27 | ||
28 | struct lttng_cs { | |
29 | struct lttng_stack_trace stack_trace[RING_BUFFER_MAX_NESTING]; | |
30 | }; | |
31 | ||
32 | struct field_data { | |
33 | struct lttng_cs __percpu *cs_percpu; | |
34 | enum lttng_cs_ctx_modes mode; | |
35 | }; | |
36 | ||
37 | static | |
38 | unsigned int (*save_func_kernel)(unsigned long *store, unsigned int size, | |
39 | unsigned int skipnr); | |
40 | static | |
41 | unsigned int (*save_func_user)(unsigned long *store, unsigned int size); | |
42 | ||
43 | static | |
44 | const char *lttng_cs_ctx_mode_name(enum lttng_cs_ctx_modes mode) | |
45 | { | |
46 | switch (mode) { | |
47 | case CALLSTACK_KERNEL: | |
48 | return "callstack_kernel"; | |
49 | case CALLSTACK_USER: | |
50 | return "callstack_user"; | |
51 | default: | |
52 | return NULL; | |
53 | } | |
54 | } | |
55 | ||
56 | static | |
57 | int init_type_callstack_kernel(void) | |
58 | { | |
59 | unsigned long func; | |
60 | const char *func_name = "stack_trace_save"; | |
61 | ||
62 | if (save_func_kernel) | |
63 | return 0; | |
64 | func = kallsyms_lookup_funcptr(func_name); | |
65 | if (!func) { | |
66 | printk(KERN_WARNING "LTTng: symbol lookup failed: %s\n", | |
67 | func_name); | |
68 | return -EINVAL; | |
69 | } | |
70 | save_func_kernel = (void *) func; | |
71 | return 0; | |
72 | } | |
73 | ||
74 | static | |
75 | int init_type_callstack_user(void) | |
76 | { | |
77 | unsigned long func; | |
78 | const char *func_name = "stack_trace_save_user"; | |
79 | ||
80 | if (save_func_user) | |
81 | return 0; | |
82 | func = kallsyms_lookup_funcptr(func_name); | |
83 | if (!func) { | |
84 | printk(KERN_WARNING "LTTng: symbol lookup failed: %s\n", | |
85 | func_name); | |
86 | return -EINVAL; | |
87 | } | |
88 | save_func_user = (void *) func; | |
89 | return 0; | |
90 | } | |
91 | ||
92 | static | |
93 | int init_type(enum lttng_cs_ctx_modes mode) | |
94 | { | |
95 | switch (mode) { | |
96 | case CALLSTACK_KERNEL: | |
97 | return init_type_callstack_kernel(); | |
98 | case CALLSTACK_USER: | |
99 | return init_type_callstack_user(); | |
100 | default: | |
101 | return -EINVAL; | |
102 | } | |
103 | } | |
104 | ||
105 | static | |
106 | void lttng_cs_set_init(struct lttng_cs __percpu *cs_set) | |
107 | { | |
108 | } | |
109 | ||
110 | /* Keep track of nesting inside userspace callstack context code */ | |
111 | DEFINE_PER_CPU(int, callstack_user_nesting); | |
112 | ||
113 | static | |
114 | struct lttng_stack_trace *stack_trace_context(struct lttng_ctx_field *field, | |
115 | struct lib_ring_buffer_ctx *ctx) | |
116 | { | |
117 | int buffer_nesting, cs_user_nesting; | |
118 | struct lttng_cs *cs; | |
119 | struct field_data *fdata = field->priv; | |
120 | ||
121 | /* | |
122 | * Do not gather the userspace callstack context when the event was | |
123 | * triggered by the userspace callstack context saving mechanism. | |
124 | */ | |
125 | cs_user_nesting = per_cpu(callstack_user_nesting, ctx->cpu); | |
126 | ||
127 | if (fdata->mode == CALLSTACK_USER && cs_user_nesting >= 1) | |
128 | return NULL; | |
129 | ||
130 | /* | |
131 | * get_cpu() is not required, preemption is already | |
132 | * disabled while event is written. | |
133 | * | |
134 | * max nesting is checked in lib_ring_buffer_get_cpu(). | |
135 | * Check it again as a safety net. | |
136 | */ | |
137 | cs = per_cpu_ptr(fdata->cs_percpu, ctx->cpu); | |
138 | buffer_nesting = per_cpu(lib_ring_buffer_nesting, ctx->cpu) - 1; | |
139 | if (buffer_nesting >= RING_BUFFER_MAX_NESTING) | |
140 | return NULL; | |
141 | ||
142 | return &cs->stack_trace[buffer_nesting]; | |
143 | } | |
144 | ||
145 | /* | |
146 | * In order to reserve the correct size, the callstack is computed. The | |
147 | * resulting callstack is saved to be accessed in the record step. | |
148 | */ | |
149 | static | |
150 | size_t lttng_callstack_get_size(size_t offset, struct lttng_ctx_field *field, | |
151 | struct lib_ring_buffer_ctx *ctx, | |
152 | struct lttng_channel *chan) | |
153 | { | |
154 | struct lttng_stack_trace *trace; | |
155 | struct field_data *fdata = field->priv; | |
156 | size_t orig_offset = offset; | |
157 | ||
158 | /* do not write data if no space is available */ | |
159 | trace = stack_trace_context(field, ctx); | |
160 | if (unlikely(!trace)) { | |
161 | offset += lib_ring_buffer_align(offset, lttng_alignof(unsigned int)); | |
162 | offset += sizeof(unsigned int); | |
163 | offset += lib_ring_buffer_align(offset, lttng_alignof(unsigned long)); | |
164 | return offset - orig_offset; | |
165 | } | |
166 | ||
167 | /* reset stack trace, no need to clear memory */ | |
168 | trace->nr_entries = 0; | |
169 | ||
170 | switch (fdata->mode) { | |
171 | case CALLSTACK_KERNEL: | |
172 | /* do the real work and reserve space */ | |
173 | trace->nr_entries = save_func_kernel(trace->entries, | |
174 | MAX_ENTRIES, 0); | |
175 | break; | |
176 | case CALLSTACK_USER: | |
177 | ++per_cpu(callstack_user_nesting, ctx->cpu); | |
178 | /* do the real work and reserve space */ | |
179 | trace->nr_entries = save_func_user(trace->entries, | |
180 | MAX_ENTRIES); | |
181 | per_cpu(callstack_user_nesting, ctx->cpu)--; | |
182 | break; | |
183 | default: | |
184 | WARN_ON_ONCE(1); | |
185 | } | |
186 | ||
187 | /* | |
188 | * If the array is filled, add our own marker to show that the | |
189 | * stack is incomplete. | |
190 | */ | |
191 | offset += lib_ring_buffer_align(offset, lttng_alignof(unsigned int)); | |
192 | offset += sizeof(unsigned int); | |
193 | offset += lib_ring_buffer_align(offset, lttng_alignof(unsigned long)); | |
194 | offset += sizeof(unsigned long) * trace->nr_entries; | |
195 | /* Add our own ULONG_MAX delimiter to show incomplete stack. */ | |
196 | if (trace->nr_entries == MAX_ENTRIES) | |
197 | offset += sizeof(unsigned long); | |
198 | return offset - orig_offset; | |
199 | } | |
200 | ||
201 | static | |
202 | void lttng_callstack_record(struct lttng_ctx_field *field, | |
203 | struct lib_ring_buffer_ctx *ctx, | |
204 | struct lttng_channel *chan) | |
205 | { | |
206 | struct lttng_stack_trace *trace = stack_trace_context(field, ctx); | |
207 | unsigned int nr_seq_entries; | |
208 | ||
209 | if (unlikely(!trace)) { | |
210 | nr_seq_entries = 0; | |
211 | lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned int)); | |
212 | chan->ops->event_write(ctx, &nr_seq_entries, sizeof(unsigned int)); | |
213 | lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned long)); | |
214 | return; | |
215 | } | |
216 | lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned int)); | |
217 | nr_seq_entries = trace->nr_entries; | |
218 | if (trace->nr_entries == MAX_ENTRIES) | |
219 | nr_seq_entries++; | |
220 | chan->ops->event_write(ctx, &nr_seq_entries, sizeof(unsigned int)); | |
221 | lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned long)); | |
222 | chan->ops->event_write(ctx, trace->entries, | |
223 | sizeof(unsigned long) * trace->nr_entries); | |
224 | /* Add our own ULONG_MAX delimiter to show incomplete stack. */ | |
225 | if (trace->nr_entries == MAX_ENTRIES) { | |
226 | unsigned long delim = ULONG_MAX; | |
227 | ||
228 | chan->ops->event_write(ctx, &delim, sizeof(unsigned long)); | |
229 | } | |
230 | } |