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, 40 insertions, 0 deletions

diff --git a/elf/dl-tunables.c b/elf/dl-tunables.c
index 83265bc00b..644d21d1b0 100644
--- a/elf/dl-tunables.c
+++ b/elf/dl-tunables.c
@@ -145,6 +145,13 @@ tunable_initialize (tunable_t *cur, const char *strval)
   do_tunable_update_val (cur, &val, NULL, NULL);
 }
 
+bool
+__tunable_is_initialized (tunable_id_t id)
+{
+  return tunable_list[id].initialized;
+}
+rtld_hidden_def (__tunable_is_initialized)
+
 void
 __tunable_set_val (tunable_id_t id, tunable_val_t *valp, tunable_num_t *minp,
 		   tunable_num_t *maxp)
@@ -333,6 +340,39 @@ __tunables_print (void)
     }
 }
 
+void
+__tunable_get_default (tunable_id_t id, void *valp)
+{
+  tunable_t *cur = &tunable_list[id];
+
+  switch (cur->type.type_code)
+    {
+    case TUNABLE_TYPE_UINT_64:
+	{
+	  *((uint64_t *) valp) = (uint64_t) cur->def.numval;
+	  break;
+	}
+    case TUNABLE_TYPE_INT_32:
+	{
+	  *((int32_t *) valp) = (int32_t) cur->def.numval;
+	  break;
+	}
+    case TUNABLE_TYPE_SIZE_T:
+	{
+	  *((size_t *) valp) = (size_t) cur->def.numval;
+	  break;
+	}
+    case TUNABLE_TYPE_STRING:
+	{
+	  *((const char **)valp) = cur->def.strval;
+	  break;
+	}
+    default:
+      __builtin_unreachable ();
+    }
+}
+rtld_hidden_def (__tunable_get_default)
+
 /* Set the tunable value.  This is called by the module that the tunable exists
    in. */
 void