From c8907598f58cbb4f9217c5a9147c0a01e79ba0a5 Mon Sep 17 00:00:00 2001
From: Justin Miller <justin.miller@reactos.org>
Date: Sat, 14 Feb 2026 16:26:20 -0800
Subject: [PATCH] [UEFILDR][FREELDR] Some x64 ABI violations and memory map
 fixes (#8668)

* [UEFILDR][FREELDR] Don't let LoaderPangesSpanned span half of mem space
* [FREELDR][UEFILDR] Fix x64 ABI Violations
---
 .../freeldr/freeldr/arch/uefi/amd64/uefiasm.S | 19 ++++++++++++++++++-
 boot/freeldr/freeldr/arch/uefi/uefildr.c      |  2 ++
 boot/freeldr/freeldr/arch/uefi/uefimem.c      | 11 -----------
 boot/freeldr/freeldr/ntldr/wlmemory.c         |  7 +++++++
 4 files changed, 27 insertions(+), 12 deletions(-)

diff --git a/boot/freeldr/freeldr/arch/uefi/amd64/uefiasm.S b/boot/freeldr/freeldr/arch/uefi/amd64/uefiasm.S
index c4cd78d1e0b..6da8464f036 100644
--- a/boot/freeldr/freeldr/arch/uefi/amd64/uefiasm.S
+++ b/boot/freeldr/freeldr/arch/uefi/amd64/uefiasm.S
@@ -32,6 +32,14 @@ _exituefi:
     xor rbp, rbp
     mov rsp, qword ptr UefiServiceStack[rip]
 
+    /*
+     * Maintain the MS x64 ABI for calls into C/firmware:
+     * - 16-byte alignment at call site
+     * - 32-byte shadow space reserved by the caller
+     */
+    and rsp, -16
+    sub rsp, HEX(20)
+
     /* Call the entry routine, passing the parameters */
     mov rax, UefiExitBootServices[rip]
     call rax
@@ -57,9 +65,18 @@ _exituefi:
 // void _changestack(VOID)
 PUBLIC _changestack
 _changestack:
+    /* Preserve the current stack pointer as an argument */
     mov rax, rsp
+
+    /* Switch to the basic stack top */
     mov rsp, BasicStack[rip]
-    push rax
+
+    /* Ensure proper MS x64 ABI alignment and shadow space */
+    and rsp, -16
+    sub rsp, HEX(20)
+
+    /* ExecuteLoaderCleanly(PVOID PreviousStack) */
+    mov rcx, rax
     call ExecuteLoaderCleanly[rip]
     ret
 
diff --git a/boot/freeldr/freeldr/arch/uefi/uefildr.c b/boot/freeldr/freeldr/arch/uefi/uefildr.c
index 08f7efc3ec0..52f7711b513 100644
--- a/boot/freeldr/freeldr/arch/uefi/uefildr.c
+++ b/boot/freeldr/freeldr/arch/uefi/uefildr.c
@@ -82,6 +82,7 @@ Quit:
     return 0;
 }
 
+DECLSPEC_NORETURN
 void
 ExecuteLoaderCleanly(PVOID PreviousStack)
 {
@@ -89,6 +90,7 @@ ExecuteLoaderCleanly(PVOID PreviousStack)
     UefiServiceStack = PreviousStack;
 
     RunLoader();
+    Reboot();
     UNREACHABLE;
 }
 
diff --git a/boot/freeldr/freeldr/arch/uefi/uefimem.c b/boot/freeldr/freeldr/arch/uefi/uefimem.c
index 00da46a155f..cbaf3c6b885 100644
--- a/boot/freeldr/freeldr/arch/uefi/uefimem.c
+++ b/boot/freeldr/freeldr/arch/uefi/uefimem.c
@@ -27,7 +27,6 @@ AddMemoryDescriptor(
 
 /* GLOBALS *******************************************************************/
 
-extern ULONG LoaderPagesSpanned;
 extern EFI_SYSTEM_TABLE* GlobalSystemTable;
 extern EFI_HANDLE GlobalImageHandle;
 
@@ -215,16 +214,6 @@ UefiMemGetMemoryMap(ULONG *MemoryMapSize)
             }
         }
 
-        /* Sometimes our loader can be loaded into higher memory than we ever allocate */
-        if (MemoryType == LoaderLoadedProgram)
-        {
-            if (((MapEntry->PhysicalStart + (MapEntry->NumberOfPages * PAGE_SIZE)) >> EFI_PAGE_SHIFT) > LoaderPagesSpanned)
-            {
-                /* This value needs to be adjusted if this occurs */
-                LoaderPagesSpanned = ((MapEntry->PhysicalStart + (MapEntry->NumberOfPages * PAGE_SIZE)) >> EFI_PAGE_SHIFT);
-            }
-        }
-
         /* We really don't want to touch these reserved spots at all */
         if (MemoryType != LoaderReserve)
         {
diff --git a/boot/freeldr/freeldr/ntldr/wlmemory.c b/boot/freeldr/freeldr/ntldr/wlmemory.c
index 1be38e97864..9bd32bdf324 100644
--- a/boot/freeldr/freeldr/ntldr/wlmemory.c
+++ b/boot/freeldr/freeldr/ntldr/wlmemory.c
@@ -326,6 +326,13 @@ WinLdrSetupMemoryLayout(IN OUT PLOADER_PARAMETER_BLOCK LoaderBlock)
 
     WinLdrpDumpMemoryDescriptors(LoaderBlock); //FIXME: Delete!
 
+#ifdef UEFIBOOT
+    extern PVOID OsLoaderBase;
+    extern SIZE_T OsLoaderSize;
+    /* UEFILDR can be above the 2GB-ish range, we don't want to map the whole area */
+    Status = MempSetupPaging((ULONG_PTR)OsLoaderBase / PAGE_SIZE, OsLoaderSize / PAGE_SIZE, FALSE);
+#endif
+
     // Map our loader image, so we can continue running
     /*Status = MempSetupPaging(OsLoaderBase >> MM_PAGE_SHIFT, OsLoaderSize >> MM_PAGE_SHIFT);
     if (!Status)