lttng-context-callstack.c

   1 /* SPDX-License-Identifier: (GPL-2.0 or LGPL-2.1)
   2  *
   3  * lttng-context-callstack.c
   4  *
   5  * LTTng callstack event context.
   6  *
   7  * Copyright (C) 2014 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   8  * Copyright (C) 2014 Francis Giraldeau <francis.giraldeau@gmail.com>
   9  *
  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.
  14  *
  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
  18  * of CPUs:
  19  *
  20  *   size = cpus * nest * depth * sizeof(unsigned long)
  21  *
  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.
  25  *
  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.
  36  *
  37  * The symbol name resolution is left to the trace reader.
  38  */
  39
  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"
  51
  52 #ifdef CONFIG_ARCH_STACKWALK
  53 #include "lttng-context-callstack-stackwalk-impl.h"
  54 #else
  55 #include "lttng-context-callstack-legacy-impl.h"
  56 #endif
  57
  58 static
  59 void field_data_free(struct field_data *fdata)
  60 {
  61         if (!fdata)
  62                 return;
  63         free_percpu(fdata->cs_percpu);
  64         kfree(fdata);
  65 }
  66
  67 static
  68 struct field_data __percpu *field_data_create(enum lttng_cs_ctx_modes mode)
  69 {
  70         struct lttng_cs __percpu *cs_set;
  71         struct field_data *fdata;
  72
  73         fdata = kzalloc(sizeof(*fdata), GFP_KERNEL);
  74         if (!fdata)
  75                 return NULL;
  76         cs_set = alloc_percpu(struct lttng_cs);
  77         if (!cs_set)
  78                 goto error_alloc;
  79         lttng_cs_set_init(cs_set);
  80         fdata->cs_percpu = cs_set;
  81         fdata->mode = mode;
  82         return fdata;
  83
  84 error_alloc:
  85         field_data_free(fdata);
  86         return NULL;
  87 }
  88
  89 static
  90 void lttng_callstack_destroy(struct lttng_ctx_field *field)
  91 {
  92         struct field_data *fdata = field->priv;
  93
  94         field_data_free(fdata);
  95 }
  96
  97 static
  98 int __lttng_add_callstack_generic(struct lttng_ctx **ctx,
  99                 enum lttng_cs_ctx_modes mode)
 100 {
 101         const char *ctx_name = lttng_cs_ctx_mode_name(mode);
 102         struct lttng_ctx_field *field;
 103         struct field_data *fdata;
 104         int ret;
 105
 106         ret = init_type(mode);
 107         if (ret)
 108                 return ret;
 109         field = lttng_append_context(ctx);
 110         if (!field)
 111                 return -ENOMEM;
 112         if (lttng_find_context(*ctx, ctx_name)) {
 113                 ret = -EEXIST;
 114                 goto error_find;
 115         }
 116         fdata = field_data_create(mode);
 117         if (!fdata) {
 118                 ret = -ENOMEM;
 119                 goto error_create;
 120         }
 121
 122         field->event_field.name = ctx_name;
 123         field->event_field.type.atype = atype_sequence;
 124         field->event_field.type.u.sequence.elem_type.atype = atype_integer;
 125         field->event_field.type.u.sequence.elem_type.u.basic.integer.size = sizeof(unsigned long) * CHAR_BIT;
 126         field->event_field.type.u.sequence.elem_type.u.basic.integer.alignment = lttng_alignof(long) * CHAR_BIT;
 127         field->event_field.type.u.sequence.elem_type.u.basic.integer.signedness = lttng_is_signed_type(unsigned long);
 128         field->event_field.type.u.sequence.elem_type.u.basic.integer.reverse_byte_order = 0;
 129         field->event_field.type.u.sequence.elem_type.u.basic.integer.base = 16;
 130         field->event_field.type.u.sequence.elem_type.u.basic.integer.encoding = lttng_encode_none;
 131
 132         field->event_field.type.u.sequence.length_type.atype = atype_integer;
 133         field->event_field.type.u.sequence.length_type.u.basic.integer.size = sizeof(unsigned int) * CHAR_BIT;
 134         field->event_field.type.u.sequence.length_type.u.basic.integer.alignment = lttng_alignof(unsigned int) * CHAR_BIT;
 135         field->event_field.type.u.sequence.length_type.u.basic.integer.signedness = lttng_is_signed_type(unsigned int);
 136         field->event_field.type.u.sequence.length_type.u.basic.integer.reverse_byte_order = 0;
 137         field->event_field.type.u.sequence.length_type.u.basic.integer.base = 10;
 138         field->event_field.type.u.sequence.length_type.u.basic.integer.encoding = lttng_encode_none;
 139
 140         field->get_size_arg = lttng_callstack_get_size;
 141         field->record = lttng_callstack_record;
 142         field->priv = fdata;
 143         field->destroy = lttng_callstack_destroy;
 144         wrapper_vmalloc_sync_mappings();
 145         return 0;
 146
 147 error_create:
 148         field_data_free(fdata);
 149 error_find:
 150         lttng_remove_context_field(ctx, field);
 151         return ret;
 152 }
 153
 154 /**
 155  *      lttng_add_callstack_to_ctx - add callstack event context
 156  *
 157  *      @ctx: the lttng_ctx pointer to initialize
 158  *      @type: the context type
 159  *
 160  *      Supported callstack type supported:
 161  *      LTTNG_KERNEL_CONTEXT_CALLSTACK_KERNEL
 162  *              Records the callstack of the kernel
 163  *      LTTNG_KERNEL_CONTEXT_CALLSTACK_USER
 164  *              Records the callstack of the userspace program (from the kernel)
 165  *
 166  * Return 0 for success, or error code.
 167  */
 168 int lttng_add_callstack_to_ctx(struct lttng_ctx **ctx, int type)
 169 {
 170         switch (type) {
 171         case LTTNG_KERNEL_CONTEXT_CALLSTACK_KERNEL:
 172                 return __lttng_add_callstack_generic(ctx, CALLSTACK_KERNEL);
 173 #ifdef CONFIG_X86
 174         case LTTNG_KERNEL_CONTEXT_CALLSTACK_USER:
 175                 return __lttng_add_callstack_generic(ctx, CALLSTACK_USER);
 176 #endif
 177         default:
 178                 return -EINVAL;
 179         }
 180 }
 181 EXPORT_SYMBOL_GPL(lttng_add_callstack_to_ctx);