0.21.0 --- openkal 0.23: a region at an address, the hint compared

Co-authored-by: speak-agent <248744407+speak-agent@users.noreply.github.com>

Author: Sunrisepeak

README.md

@@ -5,10 +5,10 @@ written on the kernel's own calls.
 
 ```toml
 [dependencies]
-openkal = "0.22.0"
+openkal = "0.23.0"
 
 [target.'cfg(os = "macos")'.dependencies]
-openkal-macos = "0.20.0"
+openkal-macos = "0.21.0"
 ```
 
 Its purpose is as much to test the specification as to be used. A specification
@@ -167,6 +167,13 @@ same image parses as fast on Linux arm64. Since 0.17.1 it is the same kernel ide
 this system's library keeps for each thread (`pthread_threadid_np`, a name no C
 library in this ecosystem defines).
 
+## What 0.21 adds (openkal 0.23)
+
+**A region at an address.** `kal_exec_alloc_at` passes the address as a hint,
+which this kernel honours where nothing is there, and releases a mapping placed
+elsewhere: `MAP_FIXED` would replace what is there. `KAL_EXEC_PROP_PLACE` is
+claimed where executable memory is available.
+
 ## What 0.20 adds (openkal 0.22)
 
 **The null device at a position.** `KAL_SPAWN_NULL_IN`, `KAL_SPAWN_NULL_OUT` and

mcpp.toml

@@ -1,7 +1,7 @@
 [package]
 namespace   = "mcpplibs"
 name        = "openkal-macos"
-version     = "0.20.0"
+version     = "0.21.0"
 description = "An implementation of openkal for macOS, written on the kernel's own calls. Its purpose is as much to test the specification as to be used."
 license     = "Apache-2.0"
 
@@ -59,7 +59,7 @@ provides-interfaces = [
 ]
 
 [dependencies]
-openkal = "0.22.0"
+openkal = "0.23.0"
 
 [build]
 # The flags are attached to this package's own sources rather than to the whole

src/exec.cpp

@@ -161,6 +161,26 @@ void* kal_exec_alloc(kal_uintptr size) {
     return reinterpret_cast<void*>(r);
 }
 
+// AT AN ADDRESS (0.23): the address as a hint, which this kernel honours where
+// nothing is there, and the answer compared. A mapping placed elsewhere is
+// released: MAP_FIXED would replace what is there, which is the one thing a
+// reservation at an address must not do.
+void* kal_exec_alloc_at(void* at, kal_uintptr size) {
+    const okm_uptr where = reinterpret_cast<okm_uptr>(at);
+    if (size == 0 || where == 0 || (where & (granularity() - 1)) != 0) return nullptr;
+    if (!available()) return nullptr;
+    const okm_uptr bytes = round_up(static_cast<okm_uptr>(size), granularity());
+    const okm_long r = okm::sys(okm::nr_mmap, static_cast<okm_long>(where), static_cast<okm_long>(bytes),
+                                okm::prot_read | okm::prot_write,
+                                okm::map_private | okm::map_anon, -1, 0);
+    if (okm::failed(r)) return nullptr;
+    if (static_cast<okm_uptr>(r) != where) {
+        okm::sys(okm::nr_munmap, r, static_cast<okm_long>(bytes));
+        return nullptr;
+    }
+    return at;
+}
+
 int kal_exec_publish(void* p, kal_uintptr size) {
     if (p == nullptr || size == 0) return kal_err_invalid;
     const okm_uptr bytes = round_up(static_cast<okm_uptr>(size), granularity());
@@ -234,7 +254,7 @@ void kal_exec_free(void* p, kal_uintptr size) {
 // bytes reserves a second region and abandons the first, which is what the
 // header says a zero in that position means.
 kal_uintptr kal_exec_props(void) {
-    return available() ? KAL_EXEC_PROP_AVAILABLE | KAL_EXEC_PROP_FILE : 0;
+    return available() ? KAL_EXEC_PROP_AVAILABLE | KAL_EXEC_PROP_FILE | KAL_EXEC_PROP_PLACE : 0;
 }
 
 }  // extern "C"