MEDIUM: initcall: move STG_REGISTER earlier

The STG_REGISTER init level is used to register known keywords and
protocol stacks. It must be called earlier because some of the init
code already relies on it to be known. For example, "haproxy -vv"
for now is constrained to start very late only because of this.

This patch moves it between STG_LOCK and STG_ALLOC, which is fine as
it's used for static registration.

doc/internals/api/initcalls.txt

@@ -213,19 +213,24 @@ and in this execution order:
   - STG_PREPARE  : used to preset variables, pre-initialize lookup tables and
                    pre-initialize list heads
   - STG_LOCK     : used to pre-initialize locks
+  - STG_REGISTER : used to register static lists such as keywords
   - STG_ALLOC    : used to allocate the required structures
   - STG_POOL     : used to create pools
-  - STG_REGISTER : used to register static lists such as keywords
   - STG_INIT     : used to initialize subsystems
 
 Each stage is guaranteed that previous stages have successfully completed. This
-means that an INITCALL placed at stage STG_REGISTER is guaranteed that all
-pools were already created and will be usable. Conversely, an INITCALL placed
-at stage STG_PREPARE must not rely on any field that requires preliminary
+means that an INITCALL placed at stage STG_INIT is guaranteed that all pools
+were already created and will be usable. Conversely, an INITCALL placed at
+stage STG_REGISTER must not rely on any field that requires preliminary
 allocation nor initialization. A callback cannot rely on other callbacks of the
 same stage, as the execution order within a stage is undefined and essentially
 depends on the linking order.
 
+The STG_REGISTER level is made for run-time linking of the various modules that
+compose the executable. Keywords, protocols and various other elements that are
+local known to each compilation unit can will be appended into common lists at
+boot time. This is why this call is placed just before STG_ALLOC.
+
 Example: register a very early call to init_log() with no argument, and another
          call to cli_register_kw(&cli_kws) much later:
 

include/haproxy/initcall.h

@@ -63,9 +63,9 @@
 enum init_stage {
 	STG_PREPARE = 0,      // preset variables, tables, list heads
 	STG_LOCK,             // pre-initialize locks
+	STG_REGISTER,         // register static lists (keywords etc)
 	STG_ALLOC,            // allocate required structures
 	STG_POOL,             // create pools
-	STG_REGISTER,         // register static lists (keywords etc)
 	STG_INIT,             // subsystems normal initialization
 	STG_SIZE              // size of the stages array, must be last
 };
@@ -200,9 +200,9 @@ __attribute__((constructor)) static void __initcb_##linenum()      \
 /* Declare all initcall sections here */
 DECLARE_INIT_SECTION(STG_PREPARE);
 DECLARE_INIT_SECTION(STG_LOCK);
+DECLARE_INIT_SECTION(STG_REGISTER);
 DECLARE_INIT_SECTION(STG_ALLOC);
 DECLARE_INIT_SECTION(STG_POOL);
-DECLARE_INIT_SECTION(STG_REGISTER);
 DECLARE_INIT_SECTION(STG_INIT);
 
 // for use in the main haproxy.c file

src/haproxy.c

@@ -2906,9 +2906,9 @@ int main(int argc, char **argv)
 	/* process all initcalls in order of potential dependency */
 	RUN_INITCALLS(STG_PREPARE);
 	RUN_INITCALLS(STG_LOCK);
+	RUN_INITCALLS(STG_REGISTER);
 	RUN_INITCALLS(STG_ALLOC);
 	RUN_INITCALLS(STG_POOL);
-	RUN_INITCALLS(STG_REGISTER);
 	RUN_INITCALLS(STG_INIT);
 
 	init(argc, argv);