From 0265810d9a1034601356a3f6678695984dee8193 Mon Sep 17 00:00:00 2001
From: Chloe M <chloe@mensia.org>
Date: Wed, 15 Jul 2026 19:48:12 -0400
Subject: [PATCH] ptos/amd64: cpu: Add MP trampoline stub

Signed-off-by: Chloe M <chloe@mensia.org>
---
 build.sh                                      |  3 +-
 service/ptos/arch/amd64/Makefile              | 11 +++-
 service/ptos/arch/amd64/cpu/mp.c              | 51 +++++++++++++++++++
 service/ptos/arch/amd64/cpu/mp_trampoline.asm | 14 +++++
 service/ptos/arch/amd64/dev/link.ld           |  6 +++
 5 files changed, 83 insertions(+), 2 deletions(-)
 create mode 100644 service/ptos/arch/amd64/cpu/mp_trampoline.asm

diff --git a/build.sh b/build.sh
index f3d9dd9..e6e1ebe 100755
--- a/build.sh
+++ b/build.sh
@@ -37,7 +37,8 @@ build_verify() {
     check_deps      \
         clang       \
         rsync       \
-        xorriso
+        xorriso     \
+        nasm
 
     # We need build envs !!
     if [ -z "${PT_BUILD_SOURCED}" ]
diff --git a/service/ptos/arch/amd64/Makefile b/service/ptos/arch/amd64/Makefile
index 927f0b7..c97b739 100644
--- a/service/ptos/arch/amd64/Makefile
+++ b/service/ptos/arch/amd64/Makefile
@@ -33,12 +33,21 @@ CFLAGS =				\
 	-I$(PT_PROJECT_ROOT)/service/spkg/head/
 
 .PHONY: all
-all: bin
+all: trampoline bin
 
 .PHONY: bin
 bin: $(OFILES) $(ASMOFILES)
 	$(PROMPT) "LD" $(KERNEL_PATH)
 	$(SYS_LD) -Tdev/link.ld $(MISC_OFILES) -o $(KERNEL_PATH)
+	# Copy the MP trampoline
+	objcopy														\
+		--update-section .mp_trampoline=cpu/mp_trampoline.bin	\
+		$(KERNEL_PATH)											\
+		$(KERNEL_PATH)
+
+.PHONY: trampoline
+trampoline:
+	nasm -fbin cpu/mp_trampoline.asm -o cpu/mp_trampoline.bin
 
 -include $(CDFILES)
 %.o: %.c
diff --git a/service/ptos/arch/amd64/cpu/mp.c b/service/ptos/arch/amd64/cpu/mp.c
index eb78e24..129045f 100644
--- a/service/ptos/arch/amd64/cpu/mp.c
+++ b/service/ptos/arch/amd64/cpu/mp.c
@@ -7,11 +7,18 @@
  */
 
 #include <ptdef.h>
+#include <hal/page.h>
 #include <ex/trace.h>
 #include <drivers/acpi/acpi.h>
 #include <drivers/acpi/tables.h>
 #include <ke/bugcheck.h>
+#include <mm/vm.h>
 #include <machine/lapic.h>
+#include <string.h>
+
+/* Bring up region */
+#define BUA_BASE   0x9000
+#define BUA_LENGTH PAGESIZE
 
 /* Max processors to bootstrap */
 #define CPU_MAX 64
@@ -22,6 +29,13 @@
 /* Number of processor cores */
 static USHORT CoreCount = 0;
 
+/*
+ * The multiprocessor trampoline should fit within a single
+ * page and be no larger than such.
+ */
+ALIGN(8) SECTION(".mp_trampoline")
+static UCHAR MpTrampoline[BUA_LENGTH];
+
 /*
  * Bootstrap a single core
  *
@@ -32,10 +46,18 @@ static USHORT CoreCount = 0;
 static VOID
 BootstrapCore(ACPI_LOCAL_APIC *LocalApic)
 {
+    ULONG SelfId;
+
     if (LocalApic == NULL) {
         return;
     }
 
+    /* Let's not shoot ourselves in the face */
+    SelfId = MdLapicId();
+    if (LocalApic->ApicId == SelfId) {
+        return;
+    }
+
     ++CoreCount;
 }
 
@@ -78,5 +100,34 @@ MpBootstrap(VOID)
 VOID
 HalMpBootstrap(VOID)
 {
+    MMU_VAS Vas;
+    MM_RANGE TrampolineRange;
+    PT_STATUS Status;
+    VOID *BuaDest;
+
+    /* Map the BUA page */
+    HalMmuReadVas(&Vas);
+    TrampolineRange.VirtualBase = BUA_BASE;
+    TrampolineRange.PhysicalBase = BUA_BASE;
+    TrampolineRange.Length = BUA_LENGTH;
+    Status = MmMapRange(
+        &Vas,
+        &TrampolineRange,
+        PAGE_READ | PAGE_WRITE | PAGE_EXEC,
+        PAGESIZE_4K
+    );
+
+    if (PT_ERROR(Status)) {
+        KeBugCheck(
+            BUGCHECK_MISC,
+            "failed to map mp bringup area\n"
+        );
+    }
+
+    /* Copy trampoline to the BUA page */
+    BuaDest = (VOID *)BUA_BASE;
+    RtlMemCpy(BuaDest, MpTrampoline, BUA_LENGTH);
+
+    /* Start up the APs */
     MpBootstrap();
 }
diff --git a/service/ptos/arch/amd64/cpu/mp_trampoline.asm b/service/ptos/arch/amd64/cpu/mp_trampoline.asm
new file mode 100644
index 0000000..994cf94
--- /dev/null
+++ b/service/ptos/arch/amd64/cpu/mp_trampoline.asm
@@ -0,0 +1,14 @@
+;;
+;; Copyright (c) 2026, Chloe M.
+;; Provided under the BSD-3 clause.
+;;
+
+[org 0x9000]
+[global _start]
+
+_start:
+    cli
+    hlt
+    jmp _start
+
+times 4096 - ($ - $$) db 0
diff --git a/service/ptos/arch/amd64/dev/link.ld b/service/ptos/arch/amd64/dev/link.ld
index 71943dc..d2e8327 100644
--- a/service/ptos/arch/amd64/dev/link.ld
+++ b/service/ptos/arch/amd64/dev/link.ld
@@ -41,6 +41,12 @@ SECTIONS
 
     . += CONSTANT(MAXPAGESIZE);
 
+    .mp_trampoline : ALIGN(8) {
+        KEEP(*(.mp_trampoline))
+    }
+
+    . += CONSTANT(MAXPAGESIZE);
+
     .data : {
         *(.data)
     } :data