src/lib/lttng-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/ust-ringbuffer-context.h>
  14 #include <urcu/tls-compat.h>
  15 #include <assert.h>
  16 #include "common/compat/pthread.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(void *priv __attribute__((unused)),
  70                 size_t offset __attribute__((unused)))
  71 {
  72         return LTTNG_UST_ABI_PROCNAME_LEN;
  73 }
  74
  75 static
  76 void procname_record(void *priv __attribute__((unused)),
  77                  struct lttng_ust_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(void *priv __attribute__((unused)),
  88                 struct lttng_ust_ctx_value *value)
  89 {
  90         value->u.str = wrapper_getprocname();
  91 }
  92
  93 static const struct lttng_ust_ctx_field *ctx_field = lttng_ust_static_ctx_field(
  94         lttng_ust_static_event_field("procname",
  95                 lttng_ust_static_type_array_text(LTTNG_UST_ABI_PROCNAME_LEN),
  96                 false, false),
  97         procname_get_size,
  98         procname_record,
  99         procname_get_value,
 100         NULL, NULL);
 101
 102 int lttng_add_procname_to_ctx(struct lttng_ust_ctx **ctx)
 103 {
 104         int ret;
 105
 106         if (lttng_find_context(*ctx, ctx_field->event_field->name)) {
 107                 ret = -EEXIST;
 108                 goto error_find_context;
 109         }
 110         ret = lttng_ust_context_append(ctx, ctx_field);
 111         if (ret)
 112                 return ret;
 113         return 0;
 114
 115 error_find_context:
 116         return ret;
 117 }
 118
 119 /*
 120  * Force a read (imply TLS fixup for dlopen) of TLS variables.
 121  */
 122 void lttng_fixup_procname_tls(void)
 123 {
 124         asm volatile ("" : : "m" (URCU_TLS(cached_procname)[0]));
 125 }