From a4cbe3326ec37313bfd92c01c3dbf313cae4e2b8 Mon Sep 17 00:00:00 2001
From: Ayke van Laethem <aykevanlaethem@gmail.com>
Date: Mon, 5 Aug 2024 16:12:48 +0200
Subject: [PATCH] runtime: only allocate heap memory when needed

For example, with -gc=none and -gc=leaking, no heap needs to be
allocated when initializing the runtime. And some GCs (like -gc=custom)
are responsible for allocating the heap themselves.
---
 src/runtime/gc_blocks.go    | 1 +
 src/runtime/gc_custom.go    | 2 ++
 src/runtime/gc_leaking.go   | 2 ++
 src/runtime/gc_none.go      | 2 ++
 src/runtime/runtime_unix.go | 7 +++++--
 5 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/src/runtime/gc_blocks.go b/src/runtime/gc_blocks.go
index d58bfd92a..6d3286364 100644
--- a/src/runtime/gc_blocks.go
+++ b/src/runtime/gc_blocks.go
@@ -37,6 +37,7 @@ import (
 )
 
 const gcDebug = false
+const needsStaticHeap = true
 
 // Some globals + constants for the entire GC.
 
diff --git a/src/runtime/gc_custom.go b/src/runtime/gc_custom.go
index a34b7dce6..0125f1688 100644
--- a/src/runtime/gc_custom.go
+++ b/src/runtime/gc_custom.go
@@ -36,6 +36,8 @@ import (
 	"unsafe"
 )
 
+const needsStaticHeap = false
+
 // initHeap is called when the heap is first initialized at program start.
 func initHeap()
 
diff --git a/src/runtime/gc_leaking.go b/src/runtime/gc_leaking.go
index 9e84dc2a5..bdc7efe81 100644
--- a/src/runtime/gc_leaking.go
+++ b/src/runtime/gc_leaking.go
@@ -11,6 +11,8 @@ import (
 	"unsafe"
 )
 
+const needsStaticHeap = true
+
 // Ever-incrementing pointer: no memory is freed.
 var heapptr uintptr
 
diff --git a/src/runtime/gc_none.go b/src/runtime/gc_none.go
index 43d3c4904..173c1f643 100644
--- a/src/runtime/gc_none.go
+++ b/src/runtime/gc_none.go
@@ -10,6 +10,8 @@ import (
 	"unsafe"
 )
 
+const needsStaticHeap = false
+
 var gcTotalAlloc uint64 // for runtime.MemStats
 var gcMallocs uint64
 var gcFrees uint64
diff --git a/src/runtime/runtime_unix.go b/src/runtime/runtime_unix.go
index 08e3e7426..6add9157d 100644
--- a/src/runtime/runtime_unix.go
+++ b/src/runtime/runtime_unix.go
@@ -79,7 +79,10 @@ var stackTop uintptr
 //
 //export main
 func main(argc int32, argv *unsafe.Pointer) int {
-	preinit()
+	if needsStaticHeap {
+		// Allocate area for the heap if the GC needs it.
+		allocateHeap()
+	}
 
 	// Store argc and argv for later use.
 	main_argc = argc
@@ -298,7 +301,7 @@ var heapMaxSize uintptr
 
 var heapStart, heapEnd uintptr
 
-func preinit() {
+func allocateHeap() {
 	// Allocate a large chunk of virtual memory. Because it is virtual, it won't
 	// really be allocated in RAM. Memory will only be allocated when it is
 	// first touched.