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-config.h>
  14 #include <urcu/tls-compat.h>
  15 #include <assert.h>
  16 #include "compat.h"
  17
  18 /* Maximum number of nesting levels for the procname cache. */
  19 #define PROCNAME_NESTING_MAX    2
  20
  21 /*
  22  * We cache the result to ensure we don't trigger a system call for
  23  * each event.
  24  * Upon exec, procname changes, but exec takes care of throwing away
  25  * this cached version.
  26  * The procname can also change by calling prctl(). The procname should
  27  * be set for a thread before the first event is logged within this
  28  * thread.
  29  */
  30 typedef char procname_array[PROCNAME_NESTING_MAX][17];
  31
  32 static DEFINE_URCU_TLS(procname_array, cached_procname);
  33
  34 static DEFINE_URCU_TLS(int, procname_nesting);
  35
  36 static inline
  37 char *wrapper_getprocname(void)
  38 {
  39         int nesting = CMM_LOAD_SHARED(URCU_TLS(procname_nesting));
  40
  41         if (caa_unlikely(nesting >= PROCNAME_NESTING_MAX))
  42                 return "<unknown>";
  43         if (caa_unlikely(!URCU_TLS(cached_procname)[nesting][0])) {
  44                 CMM_STORE_SHARED(URCU_TLS(procname_nesting), nesting + 1);
  45                 /* Increment nesting before updating cache. */
  46                 cmm_barrier();
  47                 lttng_pthread_getname_np(URCU_TLS(cached_procname)[nesting], LTTNG_UST_ABI_PROCNAME_LEN);
  48                 URCU_TLS(cached_procname)[nesting][LTTNG_UST_ABI_PROCNAME_LEN - 1] = '\0';
  49                 /* Decrement nesting after updating cache. */
  50                 cmm_barrier();
  51                 CMM_STORE_SHARED(URCU_TLS(procname_nesting), nesting);
  52         }
  53         return URCU_TLS(cached_procname)[nesting];
  54 }
  55
  56 /* Reset should not be called from a signal handler. */
  57 void lttng_context_procname_reset(void)
  58 {
  59         CMM_STORE_SHARED(URCU_TLS(cached_procname)[1][0], '\0');
  60         CMM_STORE_SHARED(URCU_TLS(procname_nesting), 1);
  61         CMM_STORE_SHARED(URCU_TLS(cached_procname)[0][0], '\0');
  62         CMM_STORE_SHARED(URCU_TLS(procname_nesting), 0);
  63 }
  64
  65 static
  66 size_t procname_get_size(struct lttng_ctx_field *field, size_t offset)
  67 {
  68         return LTTNG_UST_ABI_PROCNAME_LEN;
  69 }
  70
  71 static
  72 void procname_record(struct lttng_ctx_field *field,
  73                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  74                  struct lttng_channel *chan)
  75 {
  76         char *procname;
  77
  78         procname = wrapper_getprocname();
  79         chan->ops->event_write(ctx, procname, LTTNG_UST_ABI_PROCNAME_LEN);
  80 }
  81
  82 static
  83 void procname_get_value(struct lttng_ctx_field *field,
  84                 struct lttng_ctx_value *value)
  85 {
  86         value->u.str = wrapper_getprocname();
  87 }
  88
  89 static const struct lttng_type procname_array_elem_type =
  90         __type_integer(char, BYTE_ORDER, 10, UTF8);
  91
  92 int lttng_add_procname_to_ctx(struct lttng_ctx **ctx)
  93 {
  94         struct lttng_ctx_field *field;
  95
  96         field = lttng_append_context(ctx);
  97         if (!field)
  98                 return -ENOMEM;
  99         if (lttng_find_context(*ctx, "procname")) {
 100                 lttng_remove_context_field(ctx, field);
 101                 return -EEXIST;
 102         }
 103         field->event_field.name = "procname";
 104         field->event_field.type.atype = atype_array_nestable;
 105         field->event_field.type.u.array_nestable.elem_type =
 106                 &procname_array_elem_type;
 107         field->event_field.type.u.array_nestable.length = LTTNG_UST_ABI_PROCNAME_LEN;
 108         field->get_size = procname_get_size;
 109         field->record = procname_record;
 110         field->get_value = procname_get_value;
 111         lttng_context_update(*ctx);
 112         return 0;
 113 }
 114
 115 /*
 116  * Force a read (imply TLS fixup for dlopen) of TLS variables.
 117  */
 118 void lttng_fixup_procname_tls(void)
 119 {
 120         asm volatile ("" : : "m" (URCU_TLS(cached_procname)[0]));
 121 }