From 0bc9e6072510b4392a4942d98d14dd1bba15f718 Mon Sep 17 00:00:00 2001
From: gingerBill <gingerBill@users.noreply.github.com>
Date: Tue, 18 Aug 2026 14:44:59 +0100
Subject: [PATCH] Use new inline `asm` for `__chkstk` on Windows AMD64

---
 base/runtime/procs_windows_amd64.odin | 50 +++++++++++++++++++++++++--
 1 file changed, 48 insertions(+), 2 deletions(-)

diff --git a/base/runtime/procs_windows_amd64.odin b/base/runtime/procs_windows_amd64.odin
index cedbc2bd8..18322e38f 100644
--- a/base/runtime/procs_windows_amd64.odin
+++ b/base/runtime/procs_windows_amd64.odin
@@ -22,6 +22,52 @@ windows_trap_type_assertion :: proc "contextless" () -> ! {
 }
 
 when ODIN_NO_CRT {
-	@(require)
-	foreign import crt_lib "procs_windows_amd64.asm"
+	@(export, link_name="_tls_index", private="file")
+	_tls_index: u32 = 0
+
+	@(export, link_name="_fltused", private="file")
+	_fltused: u32 = 0x9875
+
+	@(export, link_name="__chkstk", private="file")
+	__chkstk :: proc "naked" () {
+		internal :: asm() {
+			// Allocate 16 bytes to store values of r10 and r11
+			sub   %rsp, 0x10
+			mov   [%rsp], %r10
+			mov   [%rsp + 0x8], %r11
+			// Set r10 to point to the stack as of the moment of the function call
+			lea   %r10, [%rsp+0x18]
+			// Subtract r10 til the bottom of the stack allocation, if we overflow
+			// reset r10 to 0, we'll crash with segfault anyway
+			xor   %r11, %r11
+			sub   %r10, %rax
+			cmovb %r10, %r11
+			// Load r11 with the bottom of the stack (lowest allocated address)
+			mov   %r11, [%gs:0x10]
+			// If the bottom of the allocation is above the bottom of the stack,
+			// we don't need to probe
+			cmp   %r10, %r11
+			jnb   .end
+			// Align the bottom of the allocation down to page size
+			and   %r10w, 0xf000
+		.loop:
+			// Move the pointer to the next guard page, and touch it by loading 0
+			// into that page
+			lea   %r11, [%r11 - 0x1000]
+			mov   [%r11]:u8, 0x0
+			// Did we reach the bottom of the allocation?
+			cmp   %r10, %r11
+			jnz   .loop
+		.end:
+			// Restore previous r10 and r11 and return
+			mov   %r10, [%rsp]
+			mov   %r11, [%rsp + 0x8]
+			add   %rsp, 0x10
+			ret
+		}
+
+		internal()
+	}
+	// @(require)
+	// foreign import crt_lib "procs_windows_amd64.asm"
 }