add detour_free_unused_regions

include/mach_detours.h

@@ -205,11 +205,20 @@ bool detour_set_ignore_too_small(bool value);
 /// @brief Toggle whether to free memory allocated for trampoline regions when they are empty.
 ///
 /// Default is `true` - free unused regions upon commit.<br/>
-/// `false` means they are not freed upon commit. Note that there is no way to manually free unused regions.
+/// `false` means they are not freed upon commit. See also `detour_free_unused_regions`.
 ///
 /// @returns the previous state of the flag
 bool detour_set_retain_regions(bool value);
 
+/// @brief Frees unused trampoline memory regions
+///
+/// @note Must be called from within a transaction to maintain thread saefty.
+///
+/// @returns `err_none` on success, else:<br/>
+///     * `detour_err_wrong_thread` if the calling thread is not the owner of the transaction, or if there is no
+///       transaction. See `detour_transaction_begin`.
+mach_error_t detour_free_unused_regions();
+
 /// @brief Sets the lower bound of the memory area that will not be used for detours trampoline regions
 ///
 /// Default is `0x70000000`

src/mach_detours.c

@@ -1001,6 +1001,16 @@ bool detour_set_retain_regions(const bool value)
     return previous;
 }
 
+mach_error_t detour_free_unused_regions()
+{
+    if (s_transaction_thread != mach_thread_self()) {
+        return detour_err_wrong_thread;
+    }
+
+    internal_detour_free_unused_trampoline_regions();
+    return err_none;
+}
+
 void* detour_set_system_region_lower_bound(void* value)
 {
     void* previous = s_system_region_lower_bound;