lttng-context-callstack-legacy-impl.h

   1 /* SPDX-License-Identifier: (GPL-2.0-only or LGPL-2.1-only)
   2  *
   3  * lttng-context-callstack-legacy-impl.h
   4  *
   5  * LTTng callstack event context, legacy implementation. Targets
   6  * kernels and architectures not yet using the stacktrace common
   7  * infrastructure introduced in the upstream Linux kernel by commit
   8  * 214d8ca6ee "stacktrace: Provide common infrastructure" (merged in
   9  * Linux 5.2, then gradually introduced within architectures).
  10  *
  11  * Copyright (C) 2014 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_cs_dispatch {
  24         struct stack_trace stack_trace;
  25         unsigned long entries[MAX_ENTRIES];
  26 };
  27
  28 struct lttng_cs {
  29         struct lttng_cs_dispatch dispatch[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 struct lttng_cs_type {
  38         const char *name;
  39         const char *length_name;
  40         const char *save_func_name;
  41         void (*save_func)(struct stack_trace *trace);
  42 };
  43
  44 static struct lttng_cs_type cs_types[] = {
  45         {
  46                 .name           = "callstack_kernel",
  47                 .length_name    = "_callstack_kernel_length",
  48                 .save_func_name = "save_stack_trace",
  49                 .save_func      = NULL,
  50         },
  51         {
  52                 .name           = "callstack_user",
  53                 .length_name    = "_callstack_user_length",
  54                 .save_func_name = "save_stack_trace_user",
  55                 .save_func      = NULL,
  56         },
  57 };
  58
  59 static
  60 const char *lttng_cs_ctx_mode_name(enum lttng_cs_ctx_modes mode)
  61 {
  62         return cs_types[mode].name;
  63 }
  64
  65 static
  66 const char *lttng_cs_ctx_mode_length_name(enum lttng_cs_ctx_modes mode)
  67 {
  68         return cs_types[mode].length_name;
  69 }
  70
  71 static
  72 int init_type(enum lttng_cs_ctx_modes mode)
  73 {
  74         unsigned long func;
  75
  76         if (cs_types[mode].save_func)
  77                 return 0;
  78         func = kallsyms_lookup_funcptr(cs_types[mode].save_func_name);
  79         if (!func) {
  80                 printk(KERN_WARNING "LTTng: symbol lookup failed: %s\n",
  81                                 cs_types[mode].save_func_name);
  82                 return -EINVAL;
  83         }
  84         cs_types[mode].save_func = (void *) func;
  85         return 0;
  86 }
  87
  88 static
  89 void lttng_cs_set_init(struct lttng_cs __percpu *cs_set)
  90 {
  91         int cpu, i;
  92
  93         for_each_possible_cpu(cpu) {
  94                 struct lttng_cs *cs;
  95
  96                 cs = per_cpu_ptr(cs_set, cpu);
  97                 for (i = 0; i < RING_BUFFER_MAX_NESTING; i++) {
  98                         struct lttng_cs_dispatch *dispatch;
  99
 100                         dispatch = &cs->dispatch[i];
 101                         dispatch->stack_trace.entries = dispatch->entries;
 102                         dispatch->stack_trace.max_entries = MAX_ENTRIES;
 103                 }
 104         }
 105 }
 106
 107 /* Keep track of nesting inside userspace callstack context code */
 108 DEFINE_PER_CPU(int, callstack_user_nesting);
 109
 110 static
 111 struct stack_trace *stack_trace_context(struct lttng_ctx_field *field,
 112                                         struct lib_ring_buffer_ctx *ctx)
 113 {
 114         int buffer_nesting, cs_user_nesting;
 115         struct lttng_cs *cs;
 116         struct field_data *fdata = field->priv;
 117
 118         /*
 119          * Do not gather the userspace callstack context when the event was
 120          * triggered by the userspace callstack context saving mechanism.
 121          */
 122         cs_user_nesting = per_cpu(callstack_user_nesting, ctx->cpu);
 123
 124         if (fdata->mode == CALLSTACK_USER && cs_user_nesting >= 1)
 125                 return NULL;
 126
 127         /*
 128          * get_cpu() is not required, preemption is already
 129          * disabled while event is written.
 130          *
 131          * max nesting is checked in lib_ring_buffer_get_cpu().
 132          * Check it again as a safety net.
 133          */
 134         cs = per_cpu_ptr(fdata->cs_percpu, ctx->cpu);
 135         buffer_nesting = per_cpu(lib_ring_buffer_nesting, ctx->cpu) - 1;
 136         if (buffer_nesting >= RING_BUFFER_MAX_NESTING)
 137                 return NULL;
 138
 139         return &cs->dispatch[buffer_nesting].stack_trace;
 140 }
 141
 142 static
 143 size_t lttng_callstack_length_get_size(size_t offset, struct lttng_ctx_field *field,
 144                                 struct lib_ring_buffer_ctx *ctx,
 145                                 struct lttng_channel *chan)
 146 {
 147         size_t orig_offset = offset;
 148
 149         offset += lib_ring_buffer_align(offset, lttng_alignof(unsigned int));
 150         offset += sizeof(unsigned int);
 151         return offset - orig_offset;
 152 }
 153
 154 /*
 155  * In order to reserve the correct size, the callstack is computed. The
 156  * resulting callstack is saved to be accessed in the record step.
 157  */
 158 static
 159 size_t lttng_callstack_sequence_get_size(size_t offset, struct lttng_ctx_field *field,
 160                                         struct lib_ring_buffer_ctx *ctx,
 161                                         struct lttng_channel *chan)
 162 {
 163         struct stack_trace *trace;
 164         struct field_data *fdata = field->priv;
 165         size_t orig_offset = offset;
 166
 167         /* do not write data if no space is available */
 168         trace = stack_trace_context(field, ctx);
 169         if (unlikely(!trace)) {
 170                 offset += lib_ring_buffer_align(offset, lttng_alignof(unsigned long));
 171                 return offset - orig_offset;
 172         }
 173
 174         /* reset stack trace, no need to clear memory */
 175         trace->nr_entries = 0;
 176
 177         if (fdata->mode == CALLSTACK_USER)
 178                 ++per_cpu(callstack_user_nesting, ctx->cpu);
 179
 180         /* do the real work and reserve space */
 181         cs_types[fdata->mode].save_func(trace);
 182
 183         if (fdata->mode == CALLSTACK_USER)
 184                 per_cpu(callstack_user_nesting, ctx->cpu)--;
 185
 186         /*
 187          * Remove final ULONG_MAX delimiter. If we cannot find it, add
 188          * our own marker to show that the stack is incomplete. This is
 189          * more compact for a trace.
 190          */
 191         if (trace->nr_entries > 0
 192                         && trace->entries[trace->nr_entries - 1] == ULONG_MAX) {
 193                 trace->nr_entries--;
 194         }
 195         offset += lib_ring_buffer_align(offset, lttng_alignof(unsigned long));
 196         offset += sizeof(unsigned long) * trace->nr_entries;
 197         /* Add our own ULONG_MAX delimiter to show incomplete stack. */
 198         if (trace->nr_entries == trace->max_entries)
 199                 offset += sizeof(unsigned long);
 200         return offset - orig_offset;
 201 }
 202
 203 static
 204 void lttng_callstack_length_record(struct lttng_ctx_field *field,
 205                         struct lib_ring_buffer_ctx *ctx,
 206                         struct lttng_channel *chan)
 207 {
 208         struct stack_trace *trace = stack_trace_context(field, ctx);
 209         unsigned int nr_seq_entries;
 210
 211         lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned int));
 212         if (unlikely(!trace)) {
 213                 nr_seq_entries = 0;
 214         } else {
 215                 nr_seq_entries = trace->nr_entries;
 216                 if (trace->nr_entries == trace->max_entries)
 217                         nr_seq_entries++;
 218         }
 219         chan->ops->event_write(ctx, &nr_seq_entries, sizeof(unsigned int));
 220 }
 221 static
 222 void lttng_callstack_sequence_record(struct lttng_ctx_field *field,
 223                         struct lib_ring_buffer_ctx *ctx,
 224                         struct lttng_channel *chan)
 225 {
 226         struct stack_trace *trace = stack_trace_context(field, ctx);
 227         unsigned int nr_seq_entries;
 228
 229         lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned long));
 230         if (unlikely(!trace)) {
 231                 return;
 232         }
 233         nr_seq_entries = trace->nr_entries;
 234         if (trace->nr_entries == trace->max_entries)
 235                 nr_seq_entries++;
 236         chan->ops->event_write(ctx, trace->entries,
 237                         sizeof(unsigned long) * trace->nr_entries);
 238         /* Add our own ULONG_MAX delimiter to show incomplete stack. */
 239         if (trace->nr_entries == trace->max_entries) {
 240                 unsigned long delim = ULONG_MAX;
 241
 242                 chan->ops->event_write(ctx, &delim, sizeof(unsigned long));
 243         }
 244 }