From abab915714274070c7afff76bc014d04a8c1f78b Mon Sep 17 00:00:00 2001
From: Ben Gamari <ben@smart-cactus.org>
Date: Wed, 25 Nov 2020 10:54:31 -0500
Subject: [PATCH] rts: Allocate MBlocks with MAP_TOP_DOWN on Windows
As noted in #18991, we would previously allocate heap in low memory.
Due to this the linker, which typically *needs* low memory, would end up
competing with the heap. In longer builds we end up running out of
low memory entirely, leading to linking failures.
(cherry picked from commit a1a75aa9be2c133dd1372a08eeb6a92c31688df7)
---
rts/win32/OSMem.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/rts/win32/OSMem.c b/rts/win32/OSMem.c
index 35fe72fd58ba..07247e54b9f8 100644
--- a/rts/win32/OSMem.c
+++ b/rts/win32/OSMem.c
@@ -67,8 +67,11 @@ allocNew(uint32_t n) {
alloc_rec* rec;
rec = (alloc_rec*)stgMallocBytes(sizeof(alloc_rec),"getMBlocks: allocNew");
rec->size = ((W_)n+1)*MBLOCK_SIZE;
+ // N.B. We use MEM_TOP_DOWN here to ensure that we leave the bottom of the
+ // address space available for the linker and libraries, which in general
+ // want to live in low memory. See #18991.
rec->base =
- VirtualAlloc(NULL, rec->size, MEM_RESERVE, PAGE_READWRITE);
+ VirtualAlloc(NULL, rec->size, MEM_RESERVE | MEM_TOP_DOWN, PAGE_READWRITE);
if(rec->base==0) {
stgFree((void*)rec);
rec=0;
--
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