lttng-context-callstack-legacy-impl.h

   1 /* SPDX-License-Identifier: (GPL-2.0 or LGPL-2.1)
   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 *save_func_name;
  40         void (*save_func)(struct stack_trace *trace);
  41 };
  42
  43 static struct lttng_cs_type cs_types[] = {
  44         {
  45                 .name           = "callstack_kernel",
  46                 .save_func_name = "save_stack_trace",
  47                 .save_func      = NULL,
  48         },
  49         {
  50                 .name           = "callstack_user",
  51                 .save_func_name = "save_stack_trace_user",
  52                 .save_func      = NULL,
  53         },
  54 };
  55
  56 static
  57 const char *lttng_cs_ctx_mode_name(enum lttng_cs_ctx_modes mode)
  58 {
  59         return cs_types[mode].name;
  60 }
  61
  62 static
  63 int init_type(enum lttng_cs_ctx_modes mode)
  64 {
  65         unsigned long func;
  66
  67         if (cs_types[mode].save_func)
  68                 return 0;
  69         func = kallsyms_lookup_funcptr(cs_types[mode].save_func_name);
  70         if (!func) {
  71                 printk(KERN_WARNING "LTTng: symbol lookup failed: %s\n",
  72                                 cs_types[mode].save_func_name);
  73                 return -EINVAL;
  74         }
  75         cs_types[mode].save_func = (void *) func;
  76         return 0;
  77 }
  78
  79 static
  80 void lttng_cs_set_init(struct lttng_cs __percpu *cs_set)
  81 {
  82         int cpu, i;
  83
  84         for_each_possible_cpu(cpu) {
  85                 struct lttng_cs *cs;
  86
  87                 cs = per_cpu_ptr(cs_set, cpu);
  88                 for (i = 0; i < RING_BUFFER_MAX_NESTING; i++) {
  89                         struct lttng_cs_dispatch *dispatch;
  90
  91                         dispatch = &cs->dispatch[i];
  92                         dispatch->stack_trace.entries = dispatch->entries;
  93                         dispatch->stack_trace.max_entries = MAX_ENTRIES;
  94                 }
  95         }
  96 }
  97
  98 /* Keep track of nesting inside userspace callstack context code */
  99 DEFINE_PER_CPU(int, callstack_user_nesting);
 100
 101 static
 102 struct stack_trace *stack_trace_context(struct lttng_ctx_field *field,
 103                                         struct lib_ring_buffer_ctx *ctx)
 104 {
 105         int buffer_nesting, cs_user_nesting;
 106         struct lttng_cs *cs;
 107         struct field_data *fdata = field->priv;
 108
 109         /*
 110          * Do not gather the userspace callstack context when the event was
 111          * triggered by the userspace callstack context saving mechanism.
 112          */
 113         cs_user_nesting = per_cpu(callstack_user_nesting, ctx->cpu);
 114
 115         if (fdata->mode == CALLSTACK_USER && cs_user_nesting >= 1)
 116                 return NULL;
 117
 118         /*
 119          * get_cpu() is not required, preemption is already
 120          * disabled while event is written.
 121          *
 122          * max nesting is checked in lib_ring_buffer_get_cpu().
 123          * Check it again as a safety net.
 124          */
 125         cs = per_cpu_ptr(fdata->cs_percpu, ctx->cpu);
 126         buffer_nesting = per_cpu(lib_ring_buffer_nesting, ctx->cpu) - 1;
 127         if (buffer_nesting >= RING_BUFFER_MAX_NESTING)
 128                 return NULL;
 129
 130         return &cs->dispatch[buffer_nesting].stack_trace;
 131 }
 132
 133 /*
 134  * In order to reserve the correct size, the callstack is computed. The
 135  * resulting callstack is saved to be accessed in the record step.
 136  */
 137 static
 138 size_t lttng_callstack_get_size(size_t offset, struct lttng_ctx_field *field,
 139                                 struct lib_ring_buffer_ctx *ctx,
 140                                 struct lttng_channel *chan)
 141 {
 142         struct stack_trace *trace;
 143         struct field_data *fdata = field->priv;
 144         size_t orig_offset = offset;
 145
 146         /* do not write data if no space is available */
 147         trace = stack_trace_context(field, ctx);
 148         if (unlikely(!trace)) {
 149                 offset += lib_ring_buffer_align(offset, lttng_alignof(unsigned int));
 150                 offset += sizeof(unsigned int);
 151                 offset += lib_ring_buffer_align(offset, lttng_alignof(unsigned long));
 152                 return offset - orig_offset;
 153         }
 154
 155         /* reset stack trace, no need to clear memory */
 156         trace->nr_entries = 0;
 157
 158         if (fdata->mode == CALLSTACK_USER)
 159                 ++per_cpu(callstack_user_nesting, ctx->cpu);
 160
 161         /* do the real work and reserve space */
 162         cs_types[fdata->mode].save_func(trace);
 163
 164         if (fdata->mode == CALLSTACK_USER)
 165                 per_cpu(callstack_user_nesting, ctx->cpu)--;
 166
 167         /*
 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.
 171          */
 172         if (trace->nr_entries > 0
 173                         && trace->entries[trace->nr_entries - 1] == ULONG_MAX) {
 174                 trace->nr_entries--;
 175         }
 176         offset += lib_ring_buffer_align(offset, lttng_alignof(unsigned int));
 177         offset += sizeof(unsigned int);
 178         offset += lib_ring_buffer_align(offset, lttng_alignof(unsigned long));
 179         offset += 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                 offset += sizeof(unsigned long);
 183         return offset - orig_offset;
 184 }
 185
 186 static
 187 void lttng_callstack_record(struct lttng_ctx_field *field,
 188                         struct lib_ring_buffer_ctx *ctx,
 189                         struct lttng_channel *chan)
 190 {
 191         struct stack_trace *trace = stack_trace_context(field, ctx);
 192         unsigned int nr_seq_entries;
 193
 194         if (unlikely(!trace)) {
 195                 nr_seq_entries = 0;
 196                 lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned int));
 197                 chan->ops->event_write(ctx, &nr_seq_entries, sizeof(unsigned int));
 198                 lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned long));
 199                 return;
 200         }
 201         lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned int));
 202         nr_seq_entries = trace->nr_entries;
 203         if (trace->nr_entries == trace->max_entries)
 204                 nr_seq_entries++;
 205         chan->ops->event_write(ctx, &nr_seq_entries, sizeof(unsigned int));
 206         lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned long));
 207         chan->ops->event_write(ctx, trace->entries,
 208                         sizeof(unsigned long) * trace->nr_entries);
 209         /* Add our own ULONG_MAX delimiter to show incomplete stack. */
 210         if (trace->nr_entries == trace->max_entries) {
 211                 unsigned long delim = ULONG_MAX;
 212
 213                 chan->ops->event_write(ctx, &delim, sizeof(unsigned long));
 214         }
 215 }