Make use of GCC's __attribute__((unused)) (#6392)

* configure.ac: Add support for GCC's __attribute__((unused))

When compiling under GCC with -Wextra (along with -Wall) there are a lot
of compiler warnings such as

collectors/cgroups.plugin/cgroup-network.c:89:45: warning: unused parameter ‘scope’ [-Wunused-parameter]
   89 | struct iface *read_proc_net_dev(const char *scope, const char *prefix) {
      |                                 ~~~~~~~~~~~~^~~~~

Some arguments may be able to be got rid off, others won't.

GCC (and at least clang[0]) provide an __attribute__((unused))
annotation that can be used on function parameters (also on variables,
functions, labels, enums, structs etc) to inform the compiler of such
and will squash warnings of the above nature.

A check is added to configure.ac for the use of GCC (I believe $GCC will
be set to 'yes' for clang also) and if found it creates __always_unused
& __maybe_unused #define's set to __attribute__((unused)) otherwise it
just sets them empty.

If other compilers have a similar feature this check can be adjusted to
accommodate them.

The reason for the two defines is that some variables may always be
unused in a function, others may or may not depending on #ifdef's for
example. So we are able to document both cases.

Subsequent commits will start making use of these to squash such
compiler warnings.

[0]: https://clang.llvm.org/docs/AttributeReference.html#maybe-unused-unused

Signed-off-by: Andrew Clayton <andrew@zeta.digital-domain.net>

* collectors/statsd.plugin: Mark a function argument as __maybe_unused

In collectors/statsd.plugin/statsd.c the app function argument to
STATSD_APP_CHART_DIM() might be unused if NETDATA_INTERNAL_CHECKS is not
defined, then the debug() macro that it's used in from
libnetdata/log/log.h will be defined to a dummy function where none of
the arguments are used.

This fixes a compiler warning [-Wunused-parameter] when compiling with
-Wextra *and* -Wall.

Signed-off-by: Andrew Clayton <andrew@zeta.digital-domain.net>

* collectors/apps.plugin: Mark a function argument as __maybe_unused

In collectors/apps.plugin/apps_plugin.c the function
debug_print_process_tree() takes an argument 'msg' that might be unused
if NETDATA_INTERNAL_CHECKS is not defined, then debug_log() will be set
to a dummy function that takes no arguments.

This fixes a compiler warning [-Wunused-parameter] when compiling with
-Wextra *and* -Wall.

Signed-off-by: Andrew Clayton <andrew@zeta.digital-domain.net>

* libnetdata/locks/locks: Mark function arguments as __maybe_unused

In libnetdata/locks/locks.c there a number of functions that take
arguments 'file', 'function' & 'line' that might be unused if
NETDATA_INTERNAL_CHECKS is not defined, then the debug() macro that it's
used in from libnetdata/log/log.h will be defined to a dummy function
where none of the arguments are used.

This fixes compiler warnings [-Wunused-parameter] when compiling with
-Wextra *and* -Wall.

Signed-off-by: Andrew Clayton <andrew@zeta.digital-domain.net>

* libnetdata/socket/security: Mark a function argument as __maybe_unused

In libnetdata/socket/security.c the function security_info_callback()
takes an argument 'ret' that might be unused if NETDATA_INTERNAL_CHECKS
is not defined, then the debug() macro that it's used in from
libnetdata/log/log.h will be defined to a dummy function where none of
the arguments are used.

This fixes a compiler warning [-Wunused-parameter] when compiling with
-Wextra *and* -Wall.

Signed-off-by: Andrew Clayton <andrew@zeta.digital-domain.net>

* collectors/cgroups.plugin: Mark a function argument as __maybe_unused

In collectors/cgroups.plugin/cgroup-network.c the function
read_proc_net_dev() takes an argument 'scope' that might be unused if
the NETDATA_INTERNAL_CHECKS is not defined.

This fixes a compiler warning [-Wunused-parameter] when compiling with
-Wextra *and* -Wall".

Signed-off-by: Andrew Clayton <andrew@zeta.digital-domain.net>

* database/rrddim: Mark function arguments as __maybe_unused

In database/rrddim.c there a couple of functions that take a 'st'
argument that might be unused if NETDATA_INTERNAL_CHECKS is not defined,
then the debug() macro that it's used in from libnetdata/log/log.h will
be defined to a dummy function where none of the arguments are used.

This fixes compiler warnings [-Wunused-parameter] when compiling with
-Wextra *and* -Wall.

Signed-off-by: Andrew Clayton <andrew@zeta.digital-domain.net>

* database/rrdvar: Mark a function argument as __maybe_unused

In database/rrdvar.c the function rrdvar_create_and_index() take an
argument 'scope' that might be unused if NETDATA_INTERNAL_CHECKS is not
defined, then the debug() macro that it's used in from
libnetdata/log/log.h will be defined to a dummy function where none of
the arguments are used.

This fixes a compiler warning [-Wunused-parameter] when compiling with
-Wextra *and* -Wall.

Signed-off-by: Andrew Clayton <andrew@zeta.digital-domain.net>

2 files changed, 23 insertions, 12 deletions

diff --git a/libnetdata/locks/locks.c b/libnetdata/locks/locks.c
index 91e2269025..ca9a5aee95 100644
--- a/libnetdata/locks/locks.c
+++ b/libnetdata/locks/locks.c
@@ -82,7 +82,8 @@ int __netdata_mutex_unlock(netdata_mutex_t *mutex) {
     return ret;
 }
 
-int netdata_mutex_init_debug( const char *file, const char *function, const unsigned long line, netdata_mutex_t *mutex) {
+int netdata_mutex_init_debug(const char *file __maybe_unused, const char *function __maybe_unused,
+                             const unsigned long line __maybe_unused, netdata_mutex_t *mutex) {
     usec_t start = 0;
     (void)start;
 
@@ -98,7 +99,8 @@ int netdata_mutex_init_debug( const char *file, const char *function, const unsi
     return ret;
 }
 
-int netdata_mutex_lock_debug( const char *file, const char *function, const unsigned long line, netdata_mutex_t *mutex) {
+int netdata_mutex_lock_debug(const char *file __maybe_unused, const char *function __maybe_unused,
+                             const unsigned long line __maybe_unused, netdata_mutex_t *mutex) {
     usec_t start = 0;
     (void)start;
 
@@ -114,7 +116,8 @@ int netdata_mutex_lock_debug( const char *file, const char *function, const unsi
     return ret;
 }
 
-int netdata_mutex_trylock_debug( const char *file, const char *function, const unsigned long line, netdata_mutex_t *mutex) {
+int netdata_mutex_trylock_debug(const char *file __maybe_unused, const char *function __maybe_unused,
+                                const unsigned long line __maybe_unused, netdata_mutex_t *mutex) {
     usec_t start = 0;
     (void)start;
 
@@ -130,7 +133,8 @@ int netdata_mutex_trylock_debug( const char *file, const char *function, const u
     return ret;
 }
 
-int netdata_mutex_unlock_debug( const char *file, const char *function, const unsigned long line, netdata_mutex_t *mutex) {
+int netdata_mutex_unlock_debug(const char *file __maybe_unused, const char *function __maybe_unused,
+                               const unsigned long line __maybe_unused, netdata_mutex_t *mutex) {
     usec_t start = 0;
     (void)start;
 
@@ -219,7 +223,8 @@ int __netdata_rwlock_trywrlock(netdata_rwlock_t *rwlock) {
 }
 
 
-int netdata_rwlock_destroy_debug( const char *file, const char *function, const unsigned long line, netdata_rwlock_t *rwlock) {
+int netdata_rwlock_destroy_debug(const char *file __maybe_unused, const char *function __maybe_unused,
+                                 const unsigned long line __maybe_unused, netdata_rwlock_t *rwlock) {
     usec_t start = 0;
     (void)start;
 
@@ -235,7 +240,8 @@ int netdata_rwlock_destroy_debug( const char *file, const char *function, const
     return ret;
 }
 
-int netdata_rwlock_init_debug( const char *file, const char *function, const unsigned long line, netdata_rwlock_t *rwlock) {
+int netdata_rwlock_init_debug(const char *file __maybe_unused, const char *function __maybe_unused,
+                              const unsigned long line __maybe_unused, netdata_rwlock_t *rwlock) {
     usec_t start = 0;
     (void)start;
 
@@ -251,7 +257,8 @@ int netdata_rwlock_init_debug( const char *file, const char *function, const uns
     return ret;
 }
 
-int netdata_rwlock_rdlock_debug( const char *file, const char *function, const unsigned long line, netdata_rwlock_t *rwlock) {
+int netdata_rwlock_rdlock_debug(const char *file __maybe_unused, const char *function __maybe_unused,
+                                const unsigned long line __maybe_unused, netdata_rwlock_t *rwlock) {
     usec_t start = 0;
     (void)start;
 
@@ -267,7 +274,8 @@ int netdata_rwlock_rdlock_debug( const char *file, const char *function, const u
     return ret;
 }
 
-int netdata_rwlock_wrlock_debug( const char *file, const char *function, const unsigned long line, netdata_rwlock_t *rwlock) {
+int netdata_rwlock_wrlock_debug(const char *file __maybe_unused, const char *function __maybe_unused,
+                                const unsigned long line __maybe_unused, netdata_rwlock_t *rwlock) {
     usec_t start = 0;
     (void)start;
 
@@ -283,7 +291,8 @@ int netdata_rwlock_wrlock_debug( const char *file, const char *function, const u
     return ret;
 }
 
-int netdata_rwlock_unlock_debug( const char *file, const char *function, const unsigned long line, netdata_rwlock_t *rwlock) {
+int netdata_rwlock_unlock_debug(const char *file __maybe_unused, const char *function __maybe_unused,
+                                const unsigned long line __maybe_unused, netdata_rwlock_t *rwlock) {
     usec_t start = 0;
     (void)start;
 
@@ -299,7 +308,8 @@ int netdata_rwlock_unlock_debug( const char *file, const char *function, const u
     return ret;
 }
 
-int netdata_rwlock_tryrdlock_debug( const char *file, const char *function, const unsigned long line, netdata_rwlock_t *rwlock) {
+int netdata_rwlock_tryrdlock_debug(const char *file __maybe_unused, const char *function __maybe_unused,
+                                   const unsigned long line __maybe_unused, netdata_rwlock_t *rwlock) {
     usec_t start = 0;
     (void)start;
 
@@ -315,7 +325,8 @@ int netdata_rwlock_tryrdlock_debug( const char *file, const char *function, cons
     return ret;
 }
 
-int netdata_rwlock_trywrlock_debug( const char *file, const char *function, const unsigned long line, netdata_rwlock_t *rwlock) {
+int netdata_rwlock_trywrlock_debug(const char *file __maybe_unused, const char *function __maybe_unused,
+                                   const unsigned long line __maybe_unused, netdata_rwlock_t *rwlock) {
     usec_t start = 0;
     (void)start;
 
diff --git a/libnetdata/socket/security.c b/libnetdata/socket/security.c
index dcbd3f6508..7f69b17e00 100644
--- a/libnetdata/socket/security.c
+++ b/libnetdata/socket/security.c
@@ -20,7 +20,7 @@ int netdata_validate_server =  NETDATA_SSL_VALID_CERTIFICATE;
  * @param where the variable with the flags set.
  * @param ret the return of the caller
  */
-static void security_info_callback(const SSL *ssl, int where, int ret) {
+static void security_info_callback(const SSL *ssl, int where, int ret __maybe_unused) {
     (void)ssl;
     if (where & SSL_CB_ALERT) {
         debug(D_WEB_CLIENT,"SSL INFO CALLBACK %s %s", SSL_alert_type_string(ret), SSL_alert_desc_string_long(ret));