src/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 int init_type(enum lttng_cs_ctx_modes mode)
  61 {
  62         unsigned long func;
  63
  64         if (cs_types[mode].save_func)
  65                 return 0;
  66         func = kallsyms_lookup_funcptr(cs_types[mode].save_func_name);
  67         if (!func) {
  68                 printk(KERN_WARNING "LTTng: symbol lookup failed: %s\n",
  69                                 cs_types[mode].save_func_name);
  70                 return -EINVAL;
  71         }
  72         cs_types[mode].save_func = (void *) func;
  73         return 0;
  74 }
  75
  76 static
  77 void lttng_cs_set_init(struct lttng_cs __percpu *cs_set)
  78 {
  79         int cpu, i;
  80
  81         for_each_possible_cpu(cpu) {
  82                 struct lttng_cs *cs;
  83
  84                 cs = per_cpu_ptr(cs_set, cpu);
  85                 for (i = 0; i < RING_BUFFER_MAX_NESTING; i++) {
  86                         struct lttng_cs_dispatch *dispatch;
  87
  88                         dispatch = &cs->dispatch[i];
  89                         dispatch->stack_trace.entries = dispatch->entries;
  90                         dispatch->stack_trace.max_entries = MAX_ENTRIES;
  91                 }
  92         }
  93 }
  94
  95 /* Keep track of nesting inside userspace callstack context code */
  96 DEFINE_PER_CPU(int, callstack_user_nesting);
  97
  98 /*
  99  * Note: these callbacks expect to be invoked with preemption disabled across
 100  * get_size and record due to its use of a per-cpu stack.
 101  */
 102 static
 103 struct stack_trace *stack_trace_context(struct field_data *fdata, int cpu)
 104 {
 105         int buffer_nesting, cs_user_nesting;
 106         struct lttng_cs *cs;
 107
 108         /*
 109          * Do not gather the userspace callstack context when the event was
 110          * triggered by the userspace callstack context saving mechanism.
 111          */
 112         cs_user_nesting = per_cpu(callstack_user_nesting, cpu);
 113
 114         if (fdata->mode == CALLSTACK_USER && cs_user_nesting >= 1)
 115                 return NULL;
 116
 117         /*
 118          * get_cpu() is not required, preemption is already
 119          * disabled while event is written.
 120          *
 121          * max nesting is checked in lib_ring_buffer_get_cpu().
 122          * Check it again as a safety net.
 123          */
 124         cs = per_cpu_ptr(fdata->cs_percpu, cpu);
 125         buffer_nesting = per_cpu(lib_ring_buffer_nesting, cpu) - 1;
 126         if (buffer_nesting >= RING_BUFFER_MAX_NESTING)
 127                 return NULL;
 128
 129         return &cs->dispatch[buffer_nesting].stack_trace;
 130 }
 131
 132 static
 133 size_t lttng_callstack_length_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 134 {
 135         size_t orig_offset = offset;
 136
 137         offset += lib_ring_buffer_align(offset, lttng_alignof(unsigned int));
 138         offset += sizeof(unsigned int);
 139         return offset - orig_offset;
 140 }
 141
 142 /*
 143  * In order to reserve the correct size, the callstack is computed. The
 144  * resulting callstack is saved to be accessed in the record step.
 145  */
 146 static
 147 size_t lttng_callstack_sequence_get_size(void *priv, struct lttng_probe_ctx *probe_ctx, size_t offset)
 148 {
 149         struct stack_trace *trace;
 150         struct field_data *fdata = (struct field_data *) priv;
 151         size_t orig_offset = offset;
 152         int cpu = smp_processor_id();
 153
 154         /* do not write data if no space is available */
 155         trace = stack_trace_context(fdata, cpu);
 156         if (unlikely(!trace)) {
 157                 offset += lib_ring_buffer_align(offset, lttng_alignof(unsigned long));
 158                 return offset - orig_offset;
 159         }
 160
 161         /* reset stack trace, no need to clear memory */
 162         trace->nr_entries = 0;
 163
 164         if (fdata->mode == CALLSTACK_USER)
 165                 ++per_cpu(callstack_user_nesting, cpu);
 166
 167         /* do the real work and reserve space */
 168         cs_types[fdata->mode].save_func(trace);
 169
 170         if (fdata->mode == CALLSTACK_USER)
 171                 per_cpu(callstack_user_nesting, cpu)--;
 172
 173         /*
 174          * Remove final ULONG_MAX delimiter. If we cannot find it, add
 175          * our own marker to show that the stack is incomplete. This is
 176          * more compact for a trace.
 177          */
 178         if (trace->nr_entries > 0
 179                         && trace->entries[trace->nr_entries - 1] == ULONG_MAX) {
 180                 trace->nr_entries--;
 181         }
 182         offset += lib_ring_buffer_align(offset, lttng_alignof(unsigned long));
 183         offset += sizeof(unsigned long) * trace->nr_entries;
 184         /* Add our own ULONG_MAX delimiter to show incomplete stack. */
 185         if (trace->nr_entries == trace->max_entries)
 186                 offset += sizeof(unsigned long);
 187         return offset - orig_offset;
 188 }
 189
 190 static
 191 void lttng_callstack_length_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 192                         struct lib_ring_buffer_ctx *ctx,
 193                         struct lttng_channel *chan)
 194 {
 195         int cpu = ctx->priv.reserve_cpu;
 196         struct field_data *fdata = (struct field_data *) priv;
 197         struct stack_trace *trace = stack_trace_context(fdata, cpu);
 198         unsigned int nr_seq_entries;
 199
 200         lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned int));
 201         if (unlikely(!trace)) {
 202                 nr_seq_entries = 0;
 203         } else {
 204                 nr_seq_entries = trace->nr_entries;
 205                 if (trace->nr_entries == trace->max_entries)
 206                         nr_seq_entries++;
 207         }
 208         chan->ops->event_write(ctx, &nr_seq_entries, sizeof(unsigned int));
 209 }
 210 static
 211 void lttng_callstack_sequence_record(void *priv, struct lttng_probe_ctx *probe_ctx,
 212                         struct lib_ring_buffer_ctx *ctx,
 213                         struct lttng_channel *chan)
 214 {
 215         int cpu = ctx->priv.reserve_cpu;
 216         struct field_data *fdata = (struct field_data *) priv;
 217         struct stack_trace *trace = stack_trace_context(fdata, cpu);
 218         unsigned int nr_seq_entries;
 219
 220         lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned long));
 221         if (unlikely(!trace)) {
 222                 return;
 223         }
 224         nr_seq_entries = trace->nr_entries;
 225         if (trace->nr_entries == trace->max_entries)
 226                 nr_seq_entries++;
 227         chan->ops->event_write(ctx, trace->entries,
 228                         sizeof(unsigned long) * trace->nr_entries);
 229         /* Add our own ULONG_MAX delimiter to show incomplete stack. */
 230         if (trace->nr_entries == trace->max_entries) {
 231                 unsigned long delim = ULONG_MAX;
 232
 233                 chan->ops->event_write(ctx, &delim, sizeof(unsigned long));
 234         }
 235 }