From 7d8bfa8f0a7468c810d18b556e7c760aca4bea80 Mon Sep 17 00:00:00 2001
From: Aiken Harris <harraiken91@gmail.com>
Date: Thu, 9 Apr 2026 20:25:55 +0200
Subject: [PATCH] Implement support for APIC Self-InterProcessor Interrupts
 (SIPI)

---
 sdk/xtdk/amd64/hltypes.h    |  1 +
 sdk/xtdk/i686/hltypes.h     |  1 +
 xtoskrnl/hl/x86/pic.cc      | 27 +++++++++++++++++++++++++++
 xtoskrnl/includes/hl/pic.hh |  1 +
 4 files changed, 30 insertions(+)

diff --git a/sdk/xtdk/amd64/hltypes.h b/sdk/xtdk/amd64/hltypes.h
index 7faaa5d..cbbe120 100644
--- a/sdk/xtdk/amd64/hltypes.h
+++ b/sdk/xtdk/amd64/hltypes.h
@@ -134,6 +134,7 @@ typedef enum _APIC_REGISTER
     APIC_TICR     = 0x38, /* Initial Count Register for Timer */
     APIC_TCCR     = 0x39, /* Current Count Register for Timer */
     APIC_TDCR     = 0x3E, /* Timer Divide Configuration Register */
+    APIC_SIPI     = 0x3F, /* Self-IPI Register */
     APIC_EAFR     = 0x40, /* extended APIC Feature register */
     APIC_EACR     = 0x41, /* Extended APIC Control Register */
     APIC_SEOI     = 0x42, /* Specific End Of Interrupt Register */
diff --git a/sdk/xtdk/i686/hltypes.h b/sdk/xtdk/i686/hltypes.h
index ae5b151..e0f3ccc 100644
--- a/sdk/xtdk/i686/hltypes.h
+++ b/sdk/xtdk/i686/hltypes.h
@@ -141,6 +141,7 @@ typedef enum _APIC_REGISTER
     APIC_TICR     = 0x38, /* Initial Count Register for Timer */
     APIC_TCCR     = 0x39, /* Current Count Register for Timer */
     APIC_TDCR     = 0x3E, /* Timer Divide Configuration Register */
+    APIC_SIPI     = 0x3F, /* Self-IPI Register */
     APIC_EAFR     = 0x40, /* extended APIC Feature register */
     APIC_EACR     = 0x41, /* Extended APIC Control Register */
     APIC_SEOI     = 0x42, /* Specific End Of Interrupt Register */
diff --git a/xtoskrnl/hl/x86/pic.cc b/xtoskrnl/hl/x86/pic.cc
index 7a2630f..054f859 100644
--- a/xtoskrnl/hl/x86/pic.cc
+++ b/xtoskrnl/hl/x86/pic.cc
@@ -404,6 +404,33 @@ HL::Pic::SendIpi(ULONG ApicId,
     }
 }
 
+/**
+ * Sends a Self-IPI (Inter-Processor Interrupt) to the current CPU.
+ *
+ * @param Vector
+ *        Supplies the IPI vector to send.
+ *
+ * @return This routine does not return any value.
+ *
+ * @since XT 1.0
+ */
+XTAPI
+VOID
+HL::Pic::SendSelfIpi(ULONG Vector)
+{
+    /* Check current APIC mode */
+    if(ApicMode == APIC_MODE_X2APIC)
+    {
+        /* In x2APIC mode, a dedicated Self-IPI register is used */
+        WriteApicRegister(APIC_SIPI, Vector);
+    }
+    else
+    {
+        /* In xAPIC compatibility mode, ICR0 is used */
+        WriteApicRegister(APIC_ICR0, Vector | (1 << 18));
+    }
+}
+
 /**
  * Writes to the APIC register.
  *
diff --git a/xtoskrnl/includes/hl/pic.hh b/xtoskrnl/includes/hl/pic.hh
index 02b8145..5077ea7 100644
--- a/xtoskrnl/includes/hl/pic.hh
+++ b/xtoskrnl/includes/hl/pic.hh
@@ -28,6 +28,7 @@ namespace HL
             STATIC XTAPI VOID SendEoi(VOID);
             STATIC XTAPI VOID SendIpi(ULONG ApicId,
                                       ULONG Vector);
+            STATIC XTAPI VOID SendSelfIpi(ULONG Vector);
             STATIC XTFASTCALL VOID WriteApicRegister(IN APIC_REGISTER Register,
                                                      IN ULONGLONG Value);