Suppress warning about stack_base_ptr with late-model GCC.

GCC 12 complains that set_stack_base is storing the address of
a local variable in a long-lived pointer.  This is an entirely
reasonable warning (indeed, it just helped us find a bug);
but that behavior is intentional here.  We can work around it
by using __builtin_frame_address(0) instead of a specific local
variable; that produces an address a dozen or so bytes different,
in my testing, but we don't care about such a small difference.
Maybe someday a compiler lacking that function will start to issue
a similar warning, but we'll worry about that when it happens.

Patch by me, per a suggestion from Andres Freund.  Back-patch to
v12, which is as far back as the patch will go without some pain.
(Recently-established project policy would permit a back-patch as
far as 9.2, but I'm disinclined to expend the work until GCC 12
is much more widespread.)

Discussion: https://postgr.es/m/3773792.1645141467@sss.pgh.pa.us

1 files changed, 5 insertions, 6 deletions

diff --git a/src/backend/utils/init/miscinit.c b/src/backend/utils/init/miscinit.c
index 8b73850d0df..e3110cda7ff 100644
--- a/src/backend/utils/init/miscinit.c
+++ b/src/backend/utils/init/miscinit.c
@@ -95,13 +95,12 @@ InitPostmasterChild(void)
 	IsUnderPostmaster = true;	/* we are a postmaster subprocess now */
 
 	/*
-	 * Set reference point for stack-depth checking. We re-do that even in the
-	 * !EXEC_BACKEND case, because there are some edge cases where processes
-	 * are started with an alternative stack (e.g. starting bgworkers when
-	 * running postgres using the rr debugger, as bgworkers are launched from
-	 * signal handlers).
+	 * Set reference point for stack-depth checking.  This might seem
+	 * redundant in !EXEC_BACKEND builds; but it's not because the postmaster
+	 * launches its children from signal handlers, so we might be running on
+	 * an alternative stack.
 	 */
-	set_stack_base();
+	(void) set_stack_base();
 
 	InitProcessGlobals();