[lttng-dev] [PATCH lttng-tools] Use initial-exec TLS model

[Mathieu Desnoyers]

Please disregard this patch. We need to investigate glibc's behavior with
initial-exec's TLS initialization further before doing those changes.

Thanks,

Mathieu

----- On Oct 19, 2017, at 10:51 AM, Mathieu Desnoyers mathieu.desnoyers at efficios.com wrote:

> The initial-exec TLS model is async-signal-safe, whereas the
> global-dynamic is not. This is especially important for the logging
> facility, because the first time a thread touches the TLS could be
> from a signal handler (correctness).
> 
> Moreover, IE is faster than GD model.
> 
> Also change the health state to the IE model, just in case we end up
> putting health progress reporting statements in signal handlers in the
> future. Given that we link against, but don't dlopen, that library, it
> is not using any of the IE backup pool, so there is no good reason for
> using the GD model.
> 
> Link: https://docs.oracle.com/cd/E23824_01/html/819-0690/chapter8-20.html
> Link:
> https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#Common-Variable-Attributes
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> ---
> configure.ac               | 7 ++++++-
> src/common/error.c         | 2 +-
> src/common/health/health.c | 2 +-
> 3 files changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/configure.ac b/configure.ac
> index 016c56ec..77316a28 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -440,7 +440,7 @@ AC_SUBST(UUID_LIBS)
> AC_CHECK_FUNC([clock_gettime], [AC_DEFINE_UNQUOTED([LTTNG_HAVE_CLOCK_GETTIME],
> 1, [Has clock_gettime() support.])])
> 
> # URCU library version needed or newer
> -m4_define([WRONG_LIBURCU_MSG], [Userspace RCU (liburcu) >= 0.9.0 is needed])
> +m4_define([WRONG_LIBURCU_MSG], [Userspace RCU (liburcu) >= 0.11.0 is needed])
> 
> # Check liburcu needed function calls
> AC_CHECK_DECL([cds_list_add], [],
> @@ -470,6 +470,11 @@ AC_CHECK_DECL([urcu_ref_get_unless_zero], [],
>         [AC_MSG_ERROR([WRONG_LIBURCU_MSG])], [[#include <urcu/ref.h>]]
> )
> 
> +#Macro added in urcu 0.11.0
> +AC_CHECK_DECL([DEFINE_URCU_TLS_IE], [],
> +	[AC_MSG_ERROR([WRONG_LIBURCU_MSG])], [[#include <urcu/tls-compat.h>]]
> +)
> +
> # Check for libkmod, it will be auto-neabled if found but won't fail if it's
> not,
> # it can be explicitly disabled with --without-kmod
> AH_TEMPLATE([HAVE_KMOD], [Define if you have kmod support])
> diff --git a/src/common/error.c b/src/common/error.c
> index 2215886d..5c45fc70 100644
> --- a/src/common/error.c
> +++ b/src/common/error.c
> @@ -36,7 +36,7 @@
> static int lttng_opt_abort_on_error = -1;
> 
> /* TLS variable that contains the time of one single log entry. */
> -DEFINE_URCU_TLS(struct log_time, error_log_time);
> +DEFINE_URCU_TLS_IE(struct log_time, error_log_time);
> 
> LTTNG_HIDDEN
> const char *log_add_time(void)
> diff --git a/src/common/health/health.c b/src/common/health/health.c
> index 830b6f0e..b87c70b4 100644
> --- a/src/common/health/health.c
> +++ b/src/common/health/health.c
> @@ -54,7 +54,7 @@ struct health_app {
> };
> 
> /* Define TLS health state. */
> -DEFINE_URCU_TLS(struct health_state, health_state);
> +DEFINE_URCU_TLS_IE(struct health_state, health_state);
> 
> /*
>  * Initialize health check subsytem.
> --
> 2.11.0

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com