Kernel: Implement basic module unloading :^)

Kernel modules can now be unloaded via a syscall. They get a chance to
run some code of course. Before deallocating them, we call their
"module_fini" symbol.

Kernel/Module.h

@@ -4,10 +4,13 @@
 #include <AK/Vector.h>
 #include <Kernel/KBuffer.h>
 
+typedef void* (*ModuleInitPtr)();
+typedef void* (*ModuleFiniPtr)();
+
 struct Module {
  String name;
  Vector<KBuffer> sections;
-};
 
-typedef void* (*ModuleInitPtr)();
-typedef void* (*ModuleFiniPtr)();
+ ModuleInitPtr module_init { nullptr };
+ ModuleFiniPtr module_fini { nullptr };
+};

Kernel/Process.cpp

@@ -3418,8 +3418,6 @@ int Process::sys$module_load(const char* path, size_t path_length)
  if (!elf_image->parse())
  return -ENOEXEC;
 
- ModuleInitPtr module_init = nullptr;
-
  HashMap<String, u8*> section_storage_by_name;
 
  auto module = make<Module>();
@@ -3469,15 +3467,17 @@ int Process::sys$module_load(const char* path, size_t path_length)
  elf_image->for_each_symbol([&](const ELFImage::Symbol& symbol) {
  dbg() << " - " << symbol.type() << " '" << symbol.name() << "' @ " << (void*)symbol.value() << ", size=" << symbol.size();
  if (!strcmp(symbol.name(), "module_init")) {
- module_init = (ModuleInitPtr)(text_base + symbol.value());
+ module->module_init = (ModuleInitPtr)(text_base + symbol.value());
+ } else if (!strcmp(symbol.name(), "module_fini")) {
+ module->module_fini = (ModuleFiniPtr)(text_base + symbol.value());
  }
  return IterationDecision::Continue;
  });
 
- if (!module_init)
+ if (!module->module_init)
  return -EINVAL;
 
- module_init();
+ module->module_init();
 
  auto name = module->name;
  g_modules->set(name, move(module));
@@ -3493,6 +3493,14 @@ int Process::sys$module_unload(const char* name, size_t name_length)
 #endif
  if (!validate_read(name, name_length))
  return -EFAULT;
- // FIXME: Implement this syscall!
+
+ auto it = g_modules->find(name);
+ if (it == g_modules->end())
+ return -ENOENT;
+
+ if (it->value->module_fini)
+ it->value->module_fini();
+
+ g_modules->remove(it);
  return 0;
 }

Kernel/TestModule.cpp

@@ -1,7 +1,5 @@
 #include <Kernel/kstdio.h>
 
-extern "C" void outside_func();
-
 extern "C" void module_init()
 {
  kprintf("TestModule has booted!\n");
@@ -10,3 +8,8 @@ extern "C" void module_init()
  kprintf("i is now %d\n", i);
  }
 }
+
+extern "C" void module_fini()
+{
+ kprintf("TestModule is being removed!\n");
+}

Kernel/build-root-filesystem.sh

@@ -134,13 +134,13 @@ ln -s SoundPlayer mnt/bin/sp
 ln -s Help mnt/bin/help
 ln -s Browser mnt/bin/br
 ln -s HackStudio mnt/bin/hs
-ln -s modload mnt/bin/m
 echo "done"
 
 mkdir -p mnt/boot/
 cp kernel mnt/boot/
 
-cp TestModule.o mnt/
+mkdir -p mnt/mod/
+cp TestModule.o mnt/mod
 
 # Run local sync script, if it exists
 if [ -f sync-local.sh ]; then

Userland/modload.cpp

@@ -5,7 +5,7 @@ int main(int argc, char** argv)
 {
  (void)argc;
  (void)argv;
- const char* path = "/TestModule.o";
+ const char* path = "/mod/TestModule.o";
  int rc = module_load(path, strlen(path));
  if (rc < 0) {
  perror("module_load");

Userland/modunload.cpp

@@ -0,0 +1,15 @@
+#include <serenity.h>
+#include <string.h>
+
+int main(int argc, char** argv)
+{
+ (void)argc;
+ (void)argv;
+ const char* name = "FIXME";
+ int rc = module_unload(name, strlen(name));
+ if (rc < 0) {
+ perror("module_unload");
+ return 1;
+ }
+ return 0;
+}