elf: Add a way to check if tunable is set (BZ 27069)

The patch adds two new macros, TUNABLE_GET_DEFAULT and TUNABLE_IS_INITIALIZED,
here the former get the default value with a signature similar to
TUNABLE_GET, while the later returns whether the tunable was set by
the environment variable.

Checked on x86_64-linux-gnu.
Reviewed-by: DJ Delorie <dj@redhat.com>
Tested-by: Zhangfei Gao <zhangfei.gao@linaro.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/elf/Versions b/elf/Versions
index 4614acea3e..1591031da9 100644
--- a/elf/Versions
+++ b/elf/Versions
@@ -77,6 +77,7 @@ ld {
     _dl_signal_error;
 
     # Set value of a tunable.
+    __tunable_is_initialized;
     __tunable_get_val;
   }
 }