liblttng-ust/lttng-context-procname.c

   1 /*
   2  * SPDX-License-Identifier: LGPL-2.1-only
   3  *
   4  * Copyright (C) 2009-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   5  *
   6  * LTTng UST procname context.
   7  */
   8
   9 #define _LGPL_SOURCE
  10 #include <stddef.h>
  11 #include <lttng/ust-events.h>
  12 #include <lttng/ust-tracer.h>
  13 #include <lttng/ringbuffer-context.h>
  14 #include <urcu/tls-compat.h>
  15 #include <assert.h>
  16 #include "compat.h"
  17 #include "lttng-tracer-core.h"
  18
  19 #include "context-internal.h"
  20
  21 /* Maximum number of nesting levels for the procname cache. */
  22 #define PROCNAME_NESTING_MAX    2
  23
  24 /*
  25  * We cache the result to ensure we don't trigger a system call for
  26  * each event.
  27  * Upon exec, procname changes, but exec takes care of throwing away
  28  * this cached version.
  29  * The procname can also change by calling prctl(). The procname should
  30  * be set for a thread before the first event is logged within this
  31  * thread.
  32  */
  33 typedef char procname_array[PROCNAME_NESTING_MAX][17];
  34
  35 static DEFINE_URCU_TLS(procname_array, cached_procname);
  36
  37 static DEFINE_URCU_TLS(int, procname_nesting);
  38
  39 static inline
  40 const char *wrapper_getprocname(void)
  41 {
  42         int nesting = CMM_LOAD_SHARED(URCU_TLS(procname_nesting));
  43
  44         if (caa_unlikely(nesting >= PROCNAME_NESTING_MAX))
  45                 return "<unknown>";
  46         if (caa_unlikely(!URCU_TLS(cached_procname)[nesting][0])) {
  47                 CMM_STORE_SHARED(URCU_TLS(procname_nesting), nesting + 1);
  48                 /* Increment nesting before updating cache. */
  49                 cmm_barrier();
  50                 lttng_pthread_getname_np(URCU_TLS(cached_procname)[nesting], LTTNG_UST_ABI_PROCNAME_LEN);
  51                 URCU_TLS(cached_procname)[nesting][LTTNG_UST_ABI_PROCNAME_LEN - 1] = '\0';
  52                 /* Decrement nesting after updating cache. */
  53                 cmm_barrier();
  54                 CMM_STORE_SHARED(URCU_TLS(procname_nesting), nesting);
  55         }
  56         return URCU_TLS(cached_procname)[nesting];
  57 }
  58
  59 /* Reset should not be called from a signal handler. */
  60 void lttng_ust_context_procname_reset(void)
  61 {
  62         CMM_STORE_SHARED(URCU_TLS(cached_procname)[1][0], '\0');
  63         CMM_STORE_SHARED(URCU_TLS(procname_nesting), 1);
  64         CMM_STORE_SHARED(URCU_TLS(cached_procname)[0][0], '\0');
  65         CMM_STORE_SHARED(URCU_TLS(procname_nesting), 0);
  66 }
  67
  68 static
  69 size_t procname_get_size(struct lttng_ust_ctx_field *field __attribute__((unused)),
  70                 size_t offset __attribute__((unused)))
  71 {
  72         return LTTNG_UST_ABI_PROCNAME_LEN;
  73 }
  74
  75 static
  76 void procname_record(struct lttng_ust_ctx_field *field __attribute__((unused)),
  77                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  78                  struct lttng_ust_channel_buffer *chan)
  79 {
  80         const char *procname;
  81
  82         procname = wrapper_getprocname();
  83         chan->ops->event_write(ctx, procname, LTTNG_UST_ABI_PROCNAME_LEN, 1);
  84 }
  85
  86 static
  87 void procname_get_value(struct lttng_ust_ctx_field *field __attribute__((unused)),
  88                 struct lttng_ust_ctx_value *value)
  89 {
  90         value->u.str = wrapper_getprocname();
  91 }
  92
  93 int lttng_add_procname_to_ctx(struct lttng_ust_ctx **ctx)
  94 {
  95         struct lttng_ust_ctx_field *field;
  96         struct lttng_ust_type_common *type;
  97         int ret;
  98
  99         type = lttng_ust_create_type_array_text(LTTNG_UST_ABI_PROCNAME_LEN);
 100         if (!type)
 101                 return -ENOMEM;
 102         field = lttng_append_context(ctx);
 103         if (!field) {
 104                 ret = -ENOMEM;
 105                 goto error_context;
 106         }
 107         if (lttng_find_context(*ctx, "procname")) {
 108                 ret = -EEXIST;
 109                 goto error_find_context;
 110         }
 111         field->event_field->name = strdup("procname");
 112         if (!field->event_field->name) {
 113                 ret = -ENOMEM;
 114                 goto error_name;
 115         }
 116         field->event_field->type = type;
 117         field->get_size = procname_get_size;
 118         field->record = procname_record;
 119         field->get_value = procname_get_value;
 120         lttng_context_update(*ctx);
 121         return 0;
 122
 123 error_name:
 124 error_find_context:
 125         lttng_remove_context_field(ctx, field);
 126 error_context:
 127         lttng_ust_destroy_type(type);
 128         return ret;
 129 }
 130
 131 /*
 132  * Force a read (imply TLS fixup for dlopen) of TLS variables.
 133  */
 134 void lttng_fixup_procname_tls(void)
 135 {
 136         asm volatile ("" : : "m" (URCU_TLS(cached_procname)[0]));
 137 }