Set the stack_base_ptr in main(), not in random other places.

Previously we did this in PostmasterMain() and InitPostmasterChild(),
which meant that stack depth checking was disabled in non-postmaster
server processes, for instance in single-user mode.  That seems like
a fairly bad idea, since there's no a-priori restriction on the
complexity of queries we will run in single-user mode.  Moreover, this
led to not having quite the same stack depth limit in all processes,
which likely has no real-world effect but it offends my inner neatnik.
Setting the depth in main() guarantees that check_stack_depth() is
armed and has a consistent interpretation of stack depth in all forms
of server processes.

While at it, move the code associated with checking the stack depth
out of tcop/postgres.c (which was never a great home for it) into
a new file src/backend/utils/misc/stack_depth.c.

Discussion: https://postgr.es/m/2081982.1734393311@sss.pgh.pa.us

Author: tglsfdc

src/backend/main/main.c

@@ -113,6 +113,12 @@ main(int argc, char *argv[])
 	MyProcPid = getpid();
 	MemoryContextInit();
 
+	/*
+	 * Set reference point for stack-depth checking.  (There's no point in
+	 * enabling this before error reporting works.)
+	 */
+	(void) set_stack_base();
+
 	/*
 	 * Set up locale information
 	 */

src/backend/postmaster/postmaster.c

@@ -985,11 +985,6 @@ PostmasterMain(int argc, char *argv[])
 	 */
 	set_max_safe_fds();
 
-	/*
-	 * Set reference point for stack-depth checking.
-	 */
-	(void) set_stack_base();
-
 	/*
 	 * Initialize pipe (or process handle on Windows) that allows children to
 	 * wake up from sleep on postmaster death.

src/backend/tcop/postgres.c

@@ -94,9 +94,6 @@ bool		Log_disconnections = false;
 
 int			log_statement = LOGSTMT_NONE;
 
-/* GUC variable for maximum stack depth (measured in kilobytes) */
-int			max_stack_depth = 100;
-
 /* wait N seconds to allow attach from a debugger */
 int			PostAuthDelay = 0;
 
@@ -124,15 +121,6 @@ typedef struct BindParamCbData
  * ----------------
  */
 
-/* max_stack_depth converted to bytes for speed of checking */
-static long max_stack_depth_bytes = 100 * 1024L;
-
-/*
- * Stack base pointer -- initialized by PostmasterMain and inherited by
- * subprocesses (but see also InitPostmasterChild).
- */
-static char *stack_base_ptr = NULL;
-
 /*
  * Flag to keep track of whether we have started a transaction.
  * For extended query protocol this has to be remembered across messages.
@@ -3513,133 +3501,6 @@ ProcessInterrupts(void)
 		HandleParallelApplyMessages();
 }
 
-/*
- * set_stack_base: set up reference point for stack depth checking
- *
- * Returns the old reference point, if any.
- */
-pg_stack_base_t
-set_stack_base(void)
-{
-#ifndef HAVE__BUILTIN_FRAME_ADDRESS
-	char		stack_base;
-#endif
-	pg_stack_base_t old;
-
-	old = stack_base_ptr;
-
-	/*
-	 * Set up reference point for stack depth checking.  On recent gcc we use
-	 * __builtin_frame_address() to avoid a warning about storing a local
-	 * variable's address in a long-lived variable.
-	 */
-#ifdef HAVE__BUILTIN_FRAME_ADDRESS
-	stack_base_ptr = __builtin_frame_address(0);
-#else
-	stack_base_ptr = &stack_base;
-#endif
-
-	return old;
-}
-
-/*
- * restore_stack_base: restore reference point for stack depth checking
- *
- * This can be used after set_stack_base() to restore the old value. This
- * is currently only used in PL/Java. When PL/Java calls a backend function
- * from different thread, the thread's stack is at a different location than
- * the main thread's stack, so it sets the base pointer before the call, and
- * restores it afterwards.
- */
-void
-restore_stack_base(pg_stack_base_t base)
-{
-	stack_base_ptr = base;
-}
-
-/*
- * check_stack_depth/stack_is_too_deep: check for excessively deep recursion
- *
- * This should be called someplace in any recursive routine that might possibly
- * recurse deep enough to overflow the stack.  Most Unixen treat stack
- * overflow as an unrecoverable SIGSEGV, so we want to error out ourselves
- * before hitting the hardware limit.
- *
- * check_stack_depth() just throws an error summarily.  stack_is_too_deep()
- * can be used by code that wants to handle the error condition itself.
- */
-void
-check_stack_depth(void)
-{
-	if (stack_is_too_deep())
-	{
-		ereport(ERROR,
-				(errcode(ERRCODE_STATEMENT_TOO_COMPLEX),
-				 errmsg("stack depth limit exceeded"),
-				 errhint("Increase the configuration parameter \"max_stack_depth\" (currently %dkB), "
-						 "after ensuring the platform's stack depth limit is adequate.",
-						 max_stack_depth)));
-	}
-}
-
-bool
-stack_is_too_deep(void)
-{
-	char		stack_top_loc;
-	long		stack_depth;
-
-	/*
-	 * Compute distance from reference point to my local variables
-	 */
-	stack_depth = (long) (stack_base_ptr - &stack_top_loc);
-
-	/*
-	 * Take abs value, since stacks grow up on some machines, down on others
-	 */
-	if (stack_depth < 0)
-		stack_depth = -stack_depth;
-
-	/*
-	 * Trouble?
-	 *
-	 * The test on stack_base_ptr prevents us from erroring out if called
-	 * during process setup or in a non-backend process.  Logically it should
-	 * be done first, but putting it here avoids wasting cycles during normal
-	 * cases.
-	 */
-	if (stack_depth > max_stack_depth_bytes &&
-		stack_base_ptr != NULL)
-		return true;
-
-	return false;
-}
-
-/* GUC check hook for max_stack_depth */
-bool
-check_max_stack_depth(int *newval, void **extra, GucSource source)
-{
-	long		newval_bytes = *newval * 1024L;
-	long		stack_rlimit = get_stack_depth_rlimit();
-
-	if (stack_rlimit > 0 && newval_bytes > stack_rlimit - STACK_DEPTH_SLOP)
-	{
-		GUC_check_errdetail("\"max_stack_depth\" must not exceed %ldkB.",
-							(stack_rlimit - STACK_DEPTH_SLOP) / 1024L);
-		GUC_check_errhint("Increase the platform's stack depth limit via \"ulimit -s\" or local equivalent.");
-		return false;
-	}
-	return true;
-}
-
-/* GUC assign hook for max_stack_depth */
-void
-assign_max_stack_depth(int newval, void *extra)
-{
-	long		newval_bytes = newval * 1024L;
-
-	max_stack_depth_bytes = newval_bytes;
-}
-
 /*
  * GUC check_hook for client_connection_check_interval
  */
@@ -5099,40 +4960,6 @@ forbidden_in_wal_sender(char firstchar)
 }
 
 
-/*
- * Obtain platform stack depth limit (in bytes)
- *
- * Return -1 if unknown
- */
-long
-get_stack_depth_rlimit(void)
-{
-#if defined(HAVE_GETRLIMIT)
-	static long val = 0;
-
-	/* This won't change after process launch, so check just once */
-	if (val == 0)
-	{
-		struct rlimit rlim;
-
-		if (getrlimit(RLIMIT_STACK, &rlim) < 0)
-			val = -1;
-		else if (rlim.rlim_cur == RLIM_INFINITY)
-			val = LONG_MAX;
-		/* rlim_cur is probably of an unsigned type, so check for overflow */
-		else if (rlim.rlim_cur >= LONG_MAX)
-			val = LONG_MAX;
-		else
-			val = rlim.rlim_cur;
-	}
-	return val;
-#else
-	/* On Windows we set the backend stack size in src/backend/Makefile */
-	return WIN32_STACK_RLIMIT;
-#endif
-}
-
-
 static struct rusage Save_r;
 static struct timeval Save_t;
 

src/backend/utils/init/miscinit.c

@@ -106,13 +106,6 @@ InitPostmasterChild(void)
 	pgwin32_signal_initialize();
 #endif
 
-	/*
-	 * Set reference point for stack-depth checking.  This might seem
-	 * redundant in !EXEC_BACKEND builds, but it's better to keep the depth
-	 * logic the same with and without that build option.
-	 */
-	(void) set_stack_base();
-
 	InitProcessGlobals();
 
 	/*

src/backend/utils/misc/Makefile

@@ -29,6 +29,7 @@ OBJS = \
 	queryenvironment.o \
 	rls.o \
 	sampling.o \
+	stack_depth.o \
 	superuser.o \
 	timeout.o \
 	tzparser.o

src/backend/utils/misc/meson.build

@@ -14,6 +14,7 @@ backend_sources += files(
   'queryenvironment.c',
   'rls.c',
   'sampling.c',
+  'stack_depth.c',
   'superuser.c',
   'timeout.c',
   'tzparser.c',