| 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 vtid context. |
| 7 | */ |
| 8 | |
| 9 | #define _LGPL_SOURCE |
| 10 | #include <limits.h> |
| 11 | #include <stddef.h> |
| 12 | #include <sys/types.h> |
| 13 | #include <unistd.h> |
| 14 | #include <lttng/ust-events.h> |
| 15 | #include <lttng/ust-tracer.h> |
| 16 | #include <lttng/ringbuffer-context.h> |
| 17 | #include <ust-tid.h> |
| 18 | #include <urcu/tls-compat.h> |
| 19 | |
| 20 | #include "context-internal.h" |
| 21 | #include "lttng-tracer-core.h" |
| 22 | |
| 23 | /* |
| 24 | * We cache the result to ensure we don't trigger a system call for |
| 25 | * each event. |
| 26 | */ |
| 27 | static DEFINE_URCU_TLS(pid_t, cached_vtid); |
| 28 | |
| 29 | /* |
| 30 | * Upon fork or clone, the TID assigned to our thread is not the same as |
| 31 | * we kept in cache. Luckily, we are the only thread surviving in the |
| 32 | * child process, so we can simply clear our cached version. |
| 33 | */ |
| 34 | void lttng_context_vtid_reset(void) |
| 35 | { |
| 36 | CMM_STORE_SHARED(URCU_TLS(cached_vtid), 0); |
| 37 | } |
| 38 | |
| 39 | static |
| 40 | size_t vtid_get_size(struct lttng_ust_ctx_field *field __attribute__((unused)), |
| 41 | size_t offset) |
| 42 | { |
| 43 | size_t size = 0; |
| 44 | |
| 45 | size += lttng_ust_lib_ring_buffer_align(offset, lttng_ust_rb_alignof(pid_t)); |
| 46 | size += sizeof(pid_t); |
| 47 | return size; |
| 48 | } |
| 49 | |
| 50 | static inline |
| 51 | pid_t wrapper_getvtid(void) |
| 52 | { |
| 53 | pid_t vtid; |
| 54 | |
| 55 | vtid = CMM_LOAD_SHARED(URCU_TLS(cached_vtid)); |
| 56 | if (caa_unlikely(!vtid)) { |
| 57 | vtid = lttng_gettid(); |
| 58 | CMM_STORE_SHARED(URCU_TLS(cached_vtid), vtid); |
| 59 | } |
| 60 | return vtid; |
| 61 | } |
| 62 | |
| 63 | static |
| 64 | void vtid_record(struct lttng_ust_ctx_field *field __attribute__((unused)), |
| 65 | struct lttng_ust_lib_ring_buffer_ctx *ctx, |
| 66 | struct lttng_ust_channel_buffer *chan) |
| 67 | { |
| 68 | pid_t vtid = wrapper_getvtid(); |
| 69 | |
| 70 | chan->ops->event_write(ctx, &vtid, sizeof(vtid), lttng_ust_rb_alignof(vtid)); |
| 71 | } |
| 72 | |
| 73 | static |
| 74 | void vtid_get_value(struct lttng_ust_ctx_field *field __attribute__((unused)), |
| 75 | struct lttng_ust_ctx_value *value) |
| 76 | { |
| 77 | value->u.s64 = wrapper_getvtid(); |
| 78 | } |
| 79 | |
| 80 | int lttng_add_vtid_to_ctx(struct lttng_ust_ctx **ctx) |
| 81 | { |
| 82 | struct lttng_ust_ctx_field *field; |
| 83 | struct lttng_ust_type_common *type; |
| 84 | int ret; |
| 85 | |
| 86 | type = lttng_ust_create_type_integer(sizeof(pid_t) * CHAR_BIT, |
| 87 | lttng_ust_rb_alignof(pid_t) * CHAR_BIT, |
| 88 | lttng_ust_is_signed_type(pid_t), |
| 89 | BYTE_ORDER, 10); |
| 90 | if (!type) |
| 91 | return -ENOMEM; |
| 92 | field = lttng_append_context(ctx); |
| 93 | if (!field) { |
| 94 | ret = -ENOMEM; |
| 95 | goto error_context; |
| 96 | } |
| 97 | if (lttng_find_context(*ctx, "vtid")) { |
| 98 | ret = -EEXIST; |
| 99 | goto error_find_context; |
| 100 | } |
| 101 | field->event_field->name = strdup("vtid"); |
| 102 | if (!field->event_field->name) { |
| 103 | ret = -ENOMEM; |
| 104 | goto error_name; |
| 105 | } |
| 106 | field->event_field->type = type; |
| 107 | field->get_size = vtid_get_size; |
| 108 | field->record = vtid_record; |
| 109 | field->get_value = vtid_get_value; |
| 110 | lttng_context_update(*ctx); |
| 111 | return 0; |
| 112 | |
| 113 | error_name: |
| 114 | error_find_context: |
| 115 | lttng_remove_context_field(ctx, field); |
| 116 | error_context: |
| 117 | lttng_ust_destroy_type(type); |
| 118 | return ret; |
| 119 | } |
| 120 | |
| 121 | /* |
| 122 | * Force a read (imply TLS fixup for dlopen) of TLS variables. |
| 123 | */ |
| 124 | void lttng_fixup_vtid_tls(void) |
| 125 | { |
| 126 | asm volatile ("" : : "m" (URCU_TLS(cached_vtid))); |
| 127 | } |