2 * SPDX-License-Identifier: LGPL-2.1-only
4 * Copyright (C) 2009-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
6 * LTTng UST vtid context.
12 #include <sys/types.h>
14 #include <lttng/ust-events.h>
15 #include <lttng/ust-tracer.h>
16 #include <lttng/ringbuffer-context.h>
18 #include <urcu/tls-compat.h>
20 #include "context-internal.h"
21 #include "lttng-tracer-core.h"
24 * We cache the result to ensure we don't trigger a system call for
27 static DEFINE_URCU_TLS(pid_t
, cached_vtid
);
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.
34 void lttng_context_vtid_reset(void)
36 CMM_STORE_SHARED(URCU_TLS(cached_vtid
), 0);
40 size_t vtid_get_size(void *priv
__attribute__((unused
)),
45 size
+= lttng_ust_lib_ring_buffer_align(offset
, lttng_ust_rb_alignof(pid_t
));
46 size
+= sizeof(pid_t
);
51 pid_t
wrapper_getvtid(void)
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
);
64 void vtid_record(void *priv
__attribute__((unused
)),
65 struct lttng_ust_lib_ring_buffer_ctx
*ctx
,
66 struct lttng_ust_channel_buffer
*chan
)
68 pid_t vtid
= wrapper_getvtid();
70 chan
->ops
->event_write(ctx
, &vtid
, sizeof(vtid
), lttng_ust_rb_alignof(vtid
));
74 void vtid_get_value(void *priv
__attribute__((unused
)),
75 struct lttng_ust_ctx_value
*value
)
77 value
->u
.s64
= wrapper_getvtid();
80 static const struct lttng_ust_ctx_field
*ctx_field
= lttng_ust_static_ctx_field(
81 lttng_ust_static_event_field("vtid",
82 lttng_ust_static_type_integer(sizeof(pid_t
) * CHAR_BIT
,
83 lttng_ust_rb_alignof(pid_t
) * CHAR_BIT
,
84 lttng_ust_is_signed_type(pid_t
),
92 int lttng_add_vtid_to_ctx(struct lttng_ust_ctx
**ctx
)
96 if (lttng_find_context(*ctx
, ctx_field
->event_field
->name
)) {
98 goto error_find_context
;
100 ret
= lttng_ust_context_append(ctx
, ctx_field
);
110 * Force a read (imply TLS fixup for dlopen) of TLS variables.
112 void lttng_fixup_vtid_tls(void)
114 asm volatile ("" : : "m" (URCU_TLS(cached_vtid
)));