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 #include "context-internal.h"
  19
  20 /* Maximum number of nesting levels for the procname cache. */
  21 #define PROCNAME_NESTING_MAX    2
  22
  23 /*
  24  * We cache the result to ensure we don't trigger a system call for
  25  * each event.
  26  * Upon exec, procname changes, but exec takes care of throwing away
  27  * this cached version.
  28  * The procname can also change by calling prctl(). The procname should
  29  * be set for a thread before the first event is logged within this
  30  * thread.
  31  */
  32 typedef char procname_array[PROCNAME_NESTING_MAX][17];
  33
  34 static DEFINE_URCU_TLS(procname_array, cached_procname);
  35
  36 static DEFINE_URCU_TLS(int, procname_nesting);
  37
  38 static inline
  39 char *wrapper_getprocname(void)
  40 {
  41         int nesting = CMM_LOAD_SHARED(URCU_TLS(procname_nesting));
  42
  43         if (caa_unlikely(nesting >= PROCNAME_NESTING_MAX))
  44                 return "<unknown>";
  45         if (caa_unlikely(!URCU_TLS(cached_procname)[nesting][0])) {
  46                 CMM_STORE_SHARED(URCU_TLS(procname_nesting), nesting + 1);
  47                 /* Increment nesting before updating cache. */
  48                 cmm_barrier();
  49                 lttng_pthread_getname_np(URCU_TLS(cached_procname)[nesting], LTTNG_UST_ABI_PROCNAME_LEN);
  50                 URCU_TLS(cached_procname)[nesting][LTTNG_UST_ABI_PROCNAME_LEN - 1] = '\0';
  51                 /* Decrement nesting after updating cache. */
  52                 cmm_barrier();
  53                 CMM_STORE_SHARED(URCU_TLS(procname_nesting), nesting);
  54         }
  55         return URCU_TLS(cached_procname)[nesting];
  56 }
  57
  58 /* Reset should not be called from a signal handler. */
  59 void lttng_ust_context_procname_reset(void)
  60 {
  61         CMM_STORE_SHARED(URCU_TLS(cached_procname)[1][0], '\0');
  62         CMM_STORE_SHARED(URCU_TLS(procname_nesting), 1);
  63         CMM_STORE_SHARED(URCU_TLS(cached_procname)[0][0], '\0');
  64         CMM_STORE_SHARED(URCU_TLS(procname_nesting), 0);
  65 }
  66
  67 static
  68 size_t procname_get_size(struct lttng_ust_ctx_field *field, size_t offset)
  69 {
  70         return LTTNG_UST_ABI_PROCNAME_LEN;
  71 }
  72
  73 static
  74 void procname_record(struct lttng_ust_ctx_field *field,
  75                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  76                  struct lttng_channel *chan)
  77 {
  78         char *procname;
  79
  80         procname = wrapper_getprocname();
  81         chan->ops->event_write(ctx, procname, LTTNG_UST_ABI_PROCNAME_LEN);
  82 }
  83
  84 static
  85 void procname_get_value(struct lttng_ust_ctx_field *field,
  86                 struct lttng_ust_ctx_value *value)
  87 {
  88         value->u.str = wrapper_getprocname();
  89 }
  90
  91 static const struct lttng_type procname_array_elem_type =
  92         __type_integer(char, BYTE_ORDER, 10, UTF8);
  93
  94 int lttng_add_procname_to_ctx(struct lttng_ust_ctx **ctx)
  95 {
  96         struct lttng_ust_ctx_field *field;
  97
  98         field = lttng_append_context(ctx);
  99         if (!field)
 100                 return -ENOMEM;
 101         if (lttng_find_context(*ctx, "procname")) {
 102                 lttng_remove_context_field(ctx, field);
 103                 return -EEXIST;
 104         }
 105         field->event_field->name = "procname";
 106         field->event_field->type.atype = atype_array_nestable;
 107         field->event_field->type.u.array_nestable.elem_type =
 108                 &procname_array_elem_type;
 109         field->event_field->type.u.array_nestable.length = LTTNG_UST_ABI_PROCNAME_LEN;
 110         field->get_size = procname_get_size;
 111         field->record = procname_record;
 112         field->get_value = procname_get_value;
 113         lttng_context_update(*ctx);
 114         return 0;
 115 }
 116
 117 /*
 118  * Force a read (imply TLS fixup for dlopen) of TLS variables.
 119  */
 120 void lttng_fixup_procname_tls(void)
 121 {
 122         asm volatile ("" : : "m" (URCU_TLS(cached_procname)[0]));
 123 }