Kernel: Move syscall implementations out of Process.cpp

This is something I've been meaning to do for a long time, and here we
finally go. This patch moves all sys$foo functions out of Process.cpp
and into files in Kernel/Syscalls/.

It's not exactly one syscall per file (although it could be, but I got
a bit tired of the repetitive work here..)

This makes hacking on individual syscalls a lot less painful since you
don't have to rebuild nearly as much code every time. I'm also hopeful
that this makes it easier to understand individual syscalls. :^)

Kernel/Syscalls/pledge.cpp

@@ -0,0 +1,104 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <AK/StringView.h>
+#include <Kernel/Process.h>
+
+namespace Kernel {
+
+int Process::sys$pledge(const Syscall::SC_pledge_params* user_params)
+{
+    Syscall::SC_pledge_params params;
+    if (!validate_read_and_copy_typed(&params, user_params))
+        return -EFAULT;
+
+    if (params.promises.length > 1024 || params.execpromises.length > 1024)
+        return -E2BIG;
+
+    String promises;
+    if (params.promises.characters) {
+        promises = validate_and_copy_string_from_user(params.promises);
+        if (promises.is_null())
+            return -EFAULT;
+    }
+
+    String execpromises;
+    if (params.execpromises.characters) {
+        execpromises = validate_and_copy_string_from_user(params.execpromises);
+        if (execpromises.is_null())
+            return -EFAULT;
+    }
+
+    auto parse_pledge = [&](auto& pledge_spec, u32& mask) {
+        auto parts = pledge_spec.split_view(' ');
+        for (auto& part : parts) {
+#define __ENUMERATE_PLEDGE_PROMISE(x)   \
+    if (part == #x) {                   \
+        mask |= (1u << (u32)Pledge::x); \
+        continue;                       \
+    }
+            ENUMERATE_PLEDGE_PROMISES
+#undef __ENUMERATE_PLEDGE_PROMISE
+            if (part == "dns") {
+                // "dns" is an alias for "unix" since DNS queries go via LookupServer
+                mask |= (1u << (u32)Pledge::unix);
+                continue;
+            }
+            return false;
+        }
+        return true;
+    };
+
+    u32 new_promises;
+    u32 new_execpromises;
+
+    if (!promises.is_null()) {
+        new_promises = 0;
+        if (!parse_pledge(promises, new_promises))
+            return -EINVAL;
+        if (m_promises && (!new_promises || new_promises & ~m_promises))
+            return -EPERM;
+    } else {
+        new_promises = m_promises;
+    }
+
+    if (!execpromises.is_null()) {
+        new_execpromises = 0;
+        if (!parse_pledge(execpromises, new_execpromises))
+            return -EINVAL;
+        if (m_execpromises && (!new_execpromises || new_execpromises & ~m_execpromises))
+            return -EPERM;
+    } else {
+        new_execpromises = m_execpromises;
+    }
+
+    m_promises = new_promises;
+    m_execpromises = new_execpromises;
+
+    return 0;
+}
+
+}