--- /dev/null
+/*
+ * lttng-context-callstack.c
+ *
+ * LTTng callstack event context.
+ *
+ * Copyright (C) 2014 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ * Copyright (C) 2014 Francis Giraldeau <francis.giraldeau@gmail.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; only
+ * version 2.1 of the License.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ *
+ * The callstack context can be added to any kernel
+ * event. It records either the kernel or the userspace callstack, up to a
+ * max depth. The context is a CTF sequence, such that it uses only the space
+ * required for the number of callstack entries.
+ *
+ * It allocates callstack buffers per-CPU up to 4 interrupt nesting. This
+ * nesting limit is the same as defined in the ring buffer. It therefore uses a
+ * fixed amount of memory, proportional to the number of CPUs:
+ *
+ * size = cpus * nest * depth * sizeof(unsigned long)
+ *
+ * Which is about 800 bytes per-CPUs on 64-bit host and a depth of 25. The
+ * allocation is done at the initialization to avoid memory allocation
+ * overhead while tracing, using a shallow stack.
+ *
+ * The kernel callstack is recovered using save_stack_trace(), and the
+ * userspace callstack uses save_stack_trace_user(). They rely on frame
+ * pointers. These are usually available for the kernel, but the compiler
+ * option -fomit-frame-pointer frequently used in popular Linux distributions
+ * may cause the userspace callstack to be unreliable, and is a known
+ * limitation of this approach. If frame pointers are not available, it
+ * produces no error, but the callstack will be empty. We still provide the
+ * feature, because it works well for runtime environments having frame
+ * pointers. In the future, unwind support and/or last branch record may
+ * provide a solution to this problem.
+ *
+ * The symbol name resolution is left to the trace reader.
+ */
+
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/sched.h>
+#include <linux/utsname.h>
+#include <linux/stacktrace.h>
+#include <linux/spinlock.h>
+#include "lttng-events.h"
+#include "wrapper/ringbuffer/backend.h"
+#include "wrapper/ringbuffer/frontend.h"
+#include "wrapper/vmalloc.h"
+#include "lttng-tracer.h"
+
+#define MAX_ENTRIES 25 /* BUG: saving more than 30 entries causes trace corruption */
+
+struct lttng_cs {
+ struct stack_trace items[RING_BUFFER_MAX_NESTING];
+};
+
+struct field_data {
+ int mode;
+ struct lttng_cs __percpu *cs_percpu;
+};
+
+struct lttng_cs_type {
+ const char *name;
+ const char *save_func_name;
+ void (*save_func)(struct stack_trace *trace);
+};
+
+enum lttng_cs_ctx_modes {
+ CALLSTACK_KERNEL = 0,
+ CALLSTACK_USER = 1,
+};
+
+static struct lttng_cs_type cs_types[] = {
+ {
+ .name = "callstack_kernel",
+ .save_func_name = "save_stack_trace",
+ .save_func = NULL,
+ },
+ {
+ .name = "callstack_user",
+ .save_func_name = "save_stack_trace_user",
+ .save_func = NULL,
+ },
+};
+
+static
+int init_type(int mode)
+{
+ unsigned long func;
+
+ if (cs_types[mode].save_func)
+ return 0;
+ func = kallsyms_lookup_funcptr(cs_types[mode].save_func_name);
+ if (!func) {
+ printk(KERN_WARNING "LTTng: symbol lookup failed: %s\n",
+ cs_types[mode].save_func_name);
+ return -EINVAL;
+ }
+ cs_types[mode].save_func = (void *) func;
+ return 0;
+}
+
+static
+struct stack_trace *stack_trace_context(struct lttng_ctx_field *field,
+ struct lib_ring_buffer_ctx *ctx)
+{
+ int nesting;
+ struct lttng_cs *cs;
+ struct field_data *fdata = field->private;
+
+ /*
+ * get_cpu() is not required, preemption is already
+ * disabled while event is written.
+ *
+ * max nesting is checked in lib_ring_buffer_get_cpu().
+ * Check it again as a safety net.
+ */
+ cs = per_cpu_ptr(fdata->cs_percpu, ctx->cpu);
+ nesting = per_cpu(lib_ring_buffer_nesting, ctx->cpu) - 1;
+ if (nesting >= RING_BUFFER_MAX_NESTING) {
+ return NULL;
+ }
+ return &cs->items[nesting];
+}
+
+/*
+ * In order to reserve the correct size, the callstack is computed. The
+ * resulting callstack is saved to be accessed in the record step.
+ */
+static
+size_t lttng_callstack_get_size(size_t offset, struct lttng_ctx_field *field,
+ struct lib_ring_buffer_ctx *ctx,
+ struct lttng_channel *chan)
+{
+ size_t size = 0;
+ struct stack_trace *trace;
+ struct field_data *fdata = field->private;
+
+ /* do not write data if no space is available */
+ trace = stack_trace_context(field, ctx);
+ if (!trace)
+ return 0;
+
+ /* reset stack trace, no need to clear memory */
+ trace->nr_entries = 0;
+
+ /* do the real work and reserve space */
+ cs_types[fdata->mode].save_func(trace);
+ size += lib_ring_buffer_align(offset, lttng_alignof(unsigned int));
+ size += sizeof(unsigned int);
+ size += lib_ring_buffer_align(offset, lttng_alignof(unsigned long));
+ size += sizeof(unsigned long) * trace->nr_entries;
+ return size;
+}
+
+static
+void lttng_callstack_record(struct lttng_ctx_field *field,
+ struct lib_ring_buffer_ctx *ctx,
+ struct lttng_channel *chan)
+{
+ struct stack_trace *trace = stack_trace_context(field, ctx);
+
+ if (!trace)
+ return;
+ lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned int));
+ chan->ops->event_write(ctx, &trace->nr_entries, sizeof(unsigned int));
+ lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned long));
+ chan->ops->event_write(ctx, trace->entries,
+ sizeof(unsigned long) * trace->nr_entries);
+}
+
+static
+void field_data_free(struct field_data *fdata)
+{
+ int cpu, i;
+ struct lttng_cs *cs;
+
+ if (!fdata)
+ return;
+ for_each_possible_cpu(cpu) {
+ cs = per_cpu_ptr(fdata->cs_percpu, cpu);
+ for (i = 0; i < RING_BUFFER_MAX_NESTING; i++) {
+ kfree(cs->items[i].entries);
+ }
+ }
+ free_percpu(fdata->cs_percpu);
+ kfree(fdata);
+}
+
+static
+struct field_data __percpu *field_data_create(unsigned int entries, int type)
+{
+ int cpu, i;
+ struct stack_trace *item;
+ struct lttng_cs *cs;
+ struct lttng_cs __percpu *cs_set;
+ struct field_data* fdata;
+
+ fdata = kzalloc(sizeof(unsigned long) * entries, GFP_KERNEL);
+ if (!fdata)
+ return NULL;
+ cs_set = alloc_percpu(struct lttng_cs);
+ if (!cs_set)
+ goto error_alloc;
+
+ fdata->cs_percpu = cs_set;
+ for_each_possible_cpu(cpu) {
+ cs = per_cpu_ptr(cs_set, cpu);
+ for (i = 0; i < RING_BUFFER_MAX_NESTING; i++) {
+ item = &cs->items[i];
+ item->entries = kzalloc(sizeof(unsigned long) * entries, GFP_KERNEL);
+ if (!item->entries) {
+ goto error_alloc;
+ }
+ item->max_entries = entries;
+ }
+ }
+ fdata->mode = type;
+ return fdata;
+
+error_alloc:
+ field_data_free(fdata);
+ return NULL;
+}
+
+static
+void lttng_callstack_destroy(struct lttng_ctx_field *field)
+{
+ struct field_data *fdata = field->private;
+
+ field_data_free(fdata);
+}
+
+static
+int __lttng_add_callstack_generic(struct lttng_ctx **ctx, int mode)
+{
+ const char *ctx_name = cs_types[mode].name;
+ struct lttng_ctx_field *field;
+ struct field_data *fdata;
+ int ret;
+
+ ret = init_type(mode);
+ if (ret)
+ return ret;
+ field = lttng_append_context(ctx);
+ if (!field)
+ return -ENOMEM;
+ if (lttng_find_context(*ctx, ctx_name)) {
+ printk("%s lttng_find_context failed\n", ctx_name);
+ ret = -EEXIST;
+ goto error_find;
+ }
+ fdata = field_data_create(MAX_ENTRIES, mode);
+ if (!fdata) {
+ ret = -ENOMEM;
+ goto error_create;
+ }
+
+ field->event_field.name = ctx_name;
+ field->event_field.type.atype = atype_sequence;
+ field->event_field.type.u.sequence.elem_type.atype = atype_integer;
+ field->event_field.type.u.sequence.elem_type.u.basic.integer.size = sizeof(unsigned long) * CHAR_BIT;
+ field->event_field.type.u.sequence.elem_type.u.basic.integer.alignment = lttng_alignof(long) * CHAR_BIT;
+ field->event_field.type.u.sequence.elem_type.u.basic.integer.signedness = lttng_is_signed_type(unsigned long);
+ field->event_field.type.u.sequence.elem_type.u.basic.integer.reverse_byte_order = 0;
+ field->event_field.type.u.sequence.elem_type.u.basic.integer.base = 16;
+ field->event_field.type.u.sequence.elem_type.u.basic.integer.encoding = lttng_encode_none;
+
+ field->event_field.type.u.sequence.length_type.atype = atype_integer;
+ field->event_field.type.u.sequence.length_type.u.basic.integer.size = sizeof(unsigned int) * CHAR_BIT;
+ field->event_field.type.u.sequence.length_type.u.basic.integer.alignment = lttng_alignof(unsigned int) * CHAR_BIT;
+ field->event_field.type.u.sequence.length_type.u.basic.integer.signedness = lttng_is_signed_type(unsigned int);
+ field->event_field.type.u.sequence.length_type.u.basic.integer.reverse_byte_order = 0;
+ field->event_field.type.u.sequence.length_type.u.basic.integer.base = 10;
+ field->event_field.type.u.sequence.length_type.u.basic.integer.encoding = lttng_encode_none;
+
+ field->get_size_arg = lttng_callstack_get_size;
+ field->record = lttng_callstack_record;
+ field->private = fdata;
+ field->destroy = lttng_callstack_destroy;
+ wrapper_vmalloc_sync_all();
+ printk("lttng add-context %s\n", ctx_name);
+ return 0;
+
+error_create:
+ field_data_free(fdata);
+error_find:
+ lttng_remove_context_field(ctx, field);
+ return ret;
+}
+
+/**
+ * lttng_add_callstack_to_ctx - add callstack event context
+ *
+ * @ctx: the lttng_ctx pointer to initialize
+ * @type: the context type
+ *
+ * Supported callstack type supported:
+ * LTTNG_KERNEL_CONTEXT_CALLSTACK_KERNEL
+ * Records the callstack of the kernel
+ * LTTNG_KERNEL_CONTEXT_CALLSTACK_USER
+ * Records the callstack of the userspace program (from the kernel)
+ *
+ * Return 0 for success, or error code.
+ */
+int lttng_add_callstack_to_ctx(struct lttng_ctx **ctx, int type)
+{
+ switch (type) {
+ case LTTNG_KERNEL_CONTEXT_CALLSTACK_KERNEL:
+ return __lttng_add_callstack_generic(ctx, CALLSTACK_KERNEL);
+ case LTTNG_KERNEL_CONTEXT_CALLSTACK_USER:
+ return __lttng_add_callstack_generic(ctx, CALLSTACK_USER);
+ default:
+ return -EINVAL;
+ }
+}
+EXPORT_SYMBOL_GPL(lttng_add_callstack_to_ctx);
+
+MODULE_LICENSE("GPL and additional rights");
+MODULE_AUTHOR("Francis Giraldeau");
+MODULE_DESCRIPTION("Linux Trace Toolkit Callstack Support");
projects / lttng-modules.git / commitdiff
