From d80ec894900f66567137ae5363c717a38dbb8c06 Mon Sep 17 00:00:00 2001
From: Lysann Tranvouez <lysann.tranvouez@gmail.com>
Date: Sun, 28 Sep 2025 00:37:03 +0200
Subject: [PATCH] implement detour_transaction_begin

---
 .idea/codeStyles/Project.xml         |  18 +++++
 .idea/codeStyles/codeStyleConfig.xml |   5 ++
 .idea/editor.xml                     |  10 +++
 CMakeLists.txt                       |   2 +
 arm64/detours_arm64.h                |  53 ++++++++++++++
 detours_internal.h                   |  18 +++++
 mach_detours.c                       | 104 +++++++++++++++++++++++++--
 mach_detours.h                       |  27 ++++++-
 8 files changed, 231 insertions(+), 6 deletions(-)
 create mode 100644 .idea/codeStyles/Project.xml
 create mode 100644 .idea/codeStyles/codeStyleConfig.xml
 create mode 100644 arm64/detours_arm64.h
 create mode 100644 detours_internal.h

diff --git a/.idea/codeStyles/Project.xml b/.idea/codeStyles/Project.xml
new file mode 100644
index 0000000..0fd9b90
--- /dev/null
+++ b/.idea/codeStyles/Project.xml
@@ -0,0 +1,18 @@
+<component name="ProjectCodeStyleConfiguration">
+  <code_scheme name="Project" version="173">
+    <option name="AUTODETECT_INDENTS" value="false" />
+    <RiderCodeStyleSettings>
+      <option name="/Default/CodeStyle/CodeFormatting/CppClangFormat/EnableClangFormatSupport/@EntryValue" value="false" type="bool" />
+      <option name="/Default/CodeStyle/EditorConfig/EnableClangFormatSupport/@EntryValue" value="false" type="bool" />
+      <option name="/Default/CodeStyle/CodeFormatting/CppFormatting/ANONYMOUS_METHOD_DECLARATION_BRACES/@EntryValue" value="END_OF_LINE" type="string" />
+      <option name="/Default/CodeStyle/CodeFormatting/CppFormatting/CASE_BLOCK_BRACES/@EntryValue" value="END_OF_LINE" type="string" />
+      <option name="/Default/CodeStyle/CodeFormatting/CppFormatting/OTHER_BRACES/@EntryValue" value="END_OF_LINE" type="string" />
+      <option name="/Default/CodeStyle/CodeFormatting/CppFormatting/EXPRESSION_BRACES/@EntryValue" />
+      <option name="/Default/CodeStyle/CodeFormatting/CppFormatting/EMPTY_BLOCK_STYLE/@EntryValue" value="TOGETHER_SAME_LINE" type="string" />
+      <option name="/Default/CodeStyle/CodeFormatting/CppFormatting/ALLOW_COMMENT_AFTER_LBRACE/@EntryValue" value="true" type="bool" />
+      <option name="/Default/CodeStyle/CodeFormatting/CppFormatting/PLACE_ELSE_ON_NEW_LINE/@EntryValue" value="false" type="bool" />
+      <option name="/Default/CodeStyle/CodeFormatting/CppFormatting/PLACE_WHILE_ON_NEW_LINE/@EntryValue" value="false" type="bool" />
+      <option name="/Default/CodeStyle/CodeFormatting/CppFormatting/PLACE_CATCH_ON_NEW_LINE/@EntryValue" value="false" type="bool" />
+    </RiderCodeStyleSettings>
+  </code_scheme>
+</component>
\ No newline at end of file
diff --git a/.idea/codeStyles/codeStyleConfig.xml b/.idea/codeStyles/codeStyleConfig.xml
new file mode 100644
index 0000000..79ee123
--- /dev/null
+++ b/.idea/codeStyles/codeStyleConfig.xml
@@ -0,0 +1,5 @@
+<component name="ProjectCodeStyleConfiguration">
+  <state>
+    <option name="USE_PER_PROJECT_SETTINGS" value="true" />
+  </state>
+</component>
\ No newline at end of file
diff --git a/.idea/editor.xml b/.idea/editor.xml
index ead1d8a..0844927 100644
--- a/.idea/editor.xml
+++ b/.idea/editor.xml
@@ -244,5 +244,15 @@
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=IfStdIsConstantEvaluatedCanBeReplaced/@EntryIndexedValue" value="SUGGESTION" type="string" />
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=StdIsConstantEvaluatedWillAlwaysEvaluateToConstant/@EntryIndexedValue" value="WARNING" type="string" />
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=StringLiteralTypo/@EntryIndexedValue" value="DO_NOT_SHOW" type="string" />
+    <option name="/Default/CodeStyle/CodeFormatting/CppClangFormat/EnableClangFormatSupport/@EntryValue" value="false" type="bool" />
+    <option name="/Default/CodeStyle/CodeFormatting/CppFormatting/ALLOW_COMMENT_AFTER_LBRACE/@EntryValue" value="true" type="bool" />
+    <option name="/Default/CodeStyle/CodeFormatting/CppFormatting/ANONYMOUS_METHOD_DECLARATION_BRACES/@EntryValue" value="END_OF_LINE" type="string" />
+    <option name="/Default/CodeStyle/CodeFormatting/CppFormatting/CASE_BLOCK_BRACES/@EntryValue" value="END_OF_LINE" type="string" />
+    <option name="/Default/CodeStyle/CodeFormatting/CppFormatting/EMPTY_BLOCK_STYLE/@EntryValue" value="TOGETHER_SAME_LINE" type="string" />
+    <option name="/Default/CodeStyle/CodeFormatting/CppFormatting/OTHER_BRACES/@EntryValue" value="END_OF_LINE" type="string" />
+    <option name="/Default/CodeStyle/CodeFormatting/CppFormatting/PLACE_CATCH_ON_NEW_LINE/@EntryValue" value="false" type="bool" />
+    <option name="/Default/CodeStyle/CodeFormatting/CppFormatting/PLACE_ELSE_ON_NEW_LINE/@EntryValue" value="false" type="bool" />
+    <option name="/Default/CodeStyle/CodeFormatting/CppFormatting/PLACE_WHILE_ON_NEW_LINE/@EntryValue" value="false" type="bool" />
+    <option name="/Default/CodeStyle/EditorConfig/EnableClangFormatSupport/@EntryValue" value="false" type="bool" />
   </component>
 </project>
\ No newline at end of file
diff --git a/CMakeLists.txt b/CMakeLists.txt
index b76a736..e50253f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -6,4 +6,6 @@ set(CMAKE_C_STANDARD 23)
 add_library(mach_detours SHARED
     mach_detours.c
     mach_detours.h
+        arm64/detours_arm64.h
+        detours_internal.h
 )
diff --git a/arm64/detours_arm64.h b/arm64/detours_arm64.h
new file mode 100644
index 0000000..9120780
--- /dev/null
+++ b/arm64/detours_arm64.h
@@ -0,0 +1,53 @@
+// Copyright (c) Microsoft Corporation.  All rights reserved.
+// Copyright (c) Lysann Tranvouez.  All rights reserved.
+
+#pragma once
+#ifndef MACH_DETOURS_ARM64_H
+#define MACH_DETOURS_ARM64_H
+
+typedef struct detour_align
+{
+    uint8_t    obTarget;
+    uint8_t    obTrampoline;
+} detour_align;
+
+typedef struct detour_trampoline
+{
+    // An ARM64 instruction is 4 bytes long.
+    //
+    // The overwrite is always composed of 3 instructions (12 bytes) which perform an indirect jump
+    // using _DETOUR_TRAMPOLINE::pbDetour as the address holding the target location.
+    //
+    // Copied instructions can expand.
+    //
+    // The scheme using MovImmediate can cause an instruction
+    // to grow as much as 6 times.
+    // That would be Bcc or Tbz with a large address space:
+    //   4 instructions to form immediate
+    //   inverted tbz/bcc
+    //   br
+    //
+    // An expansion of 4 is not uncommon -- bl/blr and small address space:
+    //   3 instructions to form immediate
+    //   br or brl
+    //
+    // A theoretical maximum for rbCode is thefore 4*4*6 + 16 = 112 (another 16 for jmp to pbRemain).
+    //
+    // With literals, the maximum expansion is 5, including the literals: 4*4*5 + 16 = 96.
+    //
+    // The number is rounded up to 128. m_rbScratchDst should match this.
+    //
+    uint8_t            rbCode[128];    // target code + jmp to pbRemain
+    uint8_t            cbCode;         // size of moved target code.
+    uint8_t            cbCodeBreak[3]; // padding to make debugging easier.
+    uint8_t            rbRestore[24];  // original target code.
+    uint8_t            cbRestore;      // size of original target code.
+    uint8_t            cbRestoreBreak[3]; // padding to make debugging easier.
+    detour_align   rAlign[8];      // instruction alignment array.
+    uint8_t*          pbRemain;       // first instruction after moved code. [free list]
+    uint8_t*          pbDetour;       // first instruction of detour function.
+} detour_trampoline;
+
+static_assert(sizeof(detour_trampoline) == 192);
+
+#endif //MACH_DETOURS_ARM64_H
\ No newline at end of file
diff --git a/detours_internal.h b/detours_internal.h
new file mode 100644
index 0000000..cb03395
--- /dev/null
+++ b/detours_internal.h
@@ -0,0 +1,18 @@
+// Copyright (c) Microsoft Corporation.  All rights reserved.
+// Copyright (c) Lysann Tranvouez.  All rights reserved.
+
+#pragma once
+#ifndef MACH_DETOURS_INTERNAL_H
+#define MACH_DETOURS_INTERNAL_H
+
+#ifndef DETOUR_TRACE
+#if DETOUR_DEBUG
+#define DETOUR_TRACE(x) printf x
+#define DETOUR_BREAK()  raise(SIGTRAP)
+#else
+#define DETOUR_TRACE(x)
+#define DETOUR_BREAK()
+#endif
+#endif
+
+#endif //MACH_DETOURS_INTERNAL_H
\ No newline at end of file
diff --git a/mach_detours.c b/mach_detours.c
index 0e303ab..632d9e2 100644
--- a/mach_detours.c
+++ b/mach_detours.c
@@ -1,8 +1,104 @@
+// Copyright (c) Microsoft Corporation.  All rights reserved.
+// Copyright (c) Lysann Tranvouez.  All rights reserved.
+
 #include "mach_detours.h"
 
-#include <stdio.h>
+#include "detours_internal.h"
+#include "arm64/detours_arm64.h"
 
-void hello(void)
+#include <stdatomic.h>
+#include <stdint.h>
+
+#include <mach/mach_init.h>
+#include <mach/mach_vm.h>
+
+////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+// Trampoline Memory Management
+
+typedef struct detour_region
 {
-    printf("Hello, World!\n");
-}
\ No newline at end of file
+    uint32_t signature;
+    struct detour_region* next;  // Next region in list of regions.
+    detour_trampoline* free_list_head;  // List of free trampolines in this region.
+} detour_region;
+
+static const uint32_t DETOUR_REGION_SIGNATURE = 'Rrtd';
+static const uint32_t DETOUR_REGION_SIZE = 0x10000;
+static const uint32_t DETOUR_TRAMPOLINES_PER_REGION = (DETOUR_REGION_SIZE / sizeof(detour_trampoline)) - 1;
+static detour_region* s_regions_head = nullptr;
+static detour_region* s_default_region = nullptr;
+
+static mach_error_t internal_detour_writable_trampoline_regions()
+{
+    // Mark all the regions as writable.
+    const mach_port_t port = mach_task_self();
+    for (detour_region* pRegion = s_regions_head; pRegion != NULL; pRegion = pRegion->next) {
+        const mach_error_t error = mach_vm_protect(port, (mach_vm_address_t)pRegion, DETOUR_REGION_SIZE, false, VM_PROT_READ | VM_PROT_WRITE);
+        if (error != err_none) {
+            return error;
+        }
+    }
+    return err_none;
+}
+
+static void internal_detour_runnable_trampoline_regions()
+{
+    // Mark all the regions as executable.
+    const mach_port_t port = mach_task_self();
+    for (detour_region* pRegion = s_regions_head; pRegion != NULL; pRegion = pRegion->next) {
+        const mach_error_t error = mach_vm_protect(port, (mach_vm_address_t)pRegion, DETOUR_REGION_SIZE, false, VM_PROT_READ | VM_PROT_EXECUTE);
+        if (error != err_none) {
+            DETOUR_BREAK();
+        }
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+// Transactions
+
+typedef enum detour_operation_kind {
+    attach,
+    detach,
+} detour_operation_kind;
+
+typedef struct detour_operation
+{
+    struct detour_operation* next;
+    detour_operation_kind kind;
+    uint8_t** pointer;
+    uint8_t* target;
+    struct detour_trampoline* trampoline;
+    vm_prot_t perm;
+} detour_operation;
+
+typedef struct detour_pending_thread
+{
+    struct detour_pending_thread* next;
+    thread_t thread;
+} detour_pending_thread;
+
+static _Atomic(thread_t) s_transaction_thread = THREAD_NULL;
+static detour_operation* s_pending_operations_head = nullptr;
+static detour_pending_thread* s_pending_threads_head = nullptr;
+
+static mach_error_t s_pending_error = err_none;
+static void** s_pending_error_pointer = nullptr;
+
+mach_error_t detour_transaction_begin()
+{
+    // Make sure only one thread can start a transaction.
+    thread_t expected = THREAD_NULL;
+    // ReSharper disable once CppIncompatiblePointerConversion
+    if (!atomic_compare_exchange_strong(&s_transaction_thread, &expected, mach_thread_self())) {
+        return detour_err_in_progress;
+    }
+
+    s_pending_operations_head = nullptr;
+    s_pending_threads_head = nullptr;
+    s_pending_error_pointer = nullptr;
+
+    // Make sure the trampoline pages are writable.
+    s_pending_error = internal_detour_writable_trampoline_regions();
+
+    return s_pending_error;
+}
diff --git a/mach_detours.h b/mach_detours.h
index 3d117f4..002e880 100644
--- a/mach_detours.h
+++ b/mach_detours.h
@@ -1,3 +1,26 @@
-#pragma once
+// Copyright (c) Microsoft Corporation.  All rights reserved.
+// Copyright (c) Lysann Tranvouez.  All rights reserved.
 
-void hello();
\ No newline at end of file
+#pragma once
+#ifndef MACH_DETOURS_H
+#define MACH_DETOURS_H
+
+#include <mach/error.h>
+#include <mach/mach_types.h>
+
+typedef void* detour_func_t;
+
+#define	detour_err_in_progress	(err_local | 1)
+
+mach_error_t detour_transaction_begin();
+mach_error_t detour_transaction_abort();
+mach_error_t detour_transaction_commit();
+mach_error_t detour_transaction_commit_ex(detour_func_t** out_failed_target);
+
+mach_error_t detour_manage_thread(thread_t thread);
+
+mach_error_t detour_attach(detour_func_t* inout_pointer, detour_func_t detour);
+mach_error_t detour_attach_ex(detour_func_t* inout_pointer, detour_func_t detour, detour_func_t* out_real_trampoline, detour_func_t* out_real_target, detour_func_t* out_real_detour);
+mach_error_t detour_detach(detour_func_t* inout_pointer, detour_func_t detour);
+
+#endif // MACH_DETOURS_H