From a653c55941c699cd1e5a47af58dccf25428bd7be Mon Sep 17 00:00:00 2001
From: "Justin C. Miller" <justin@devjustinian.com>
Date: Sat, 18 May 2019 18:11:08 -0700
Subject: [PATCH] Use 0 instead of syscall_invalid in syscall jump list

---
 src/kernel/syscall.cpp | 9 ++++-----
 src/kernel/syscall.s   | 4 ++++
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/src/kernel/syscall.cpp b/src/kernel/syscall.cpp
index 2a00e46..20acd1b 100644
--- a/src/kernel/syscall.cpp
+++ b/src/kernel/syscall.cpp
@@ -145,15 +145,14 @@ syscall_enable()
 	static constexpr unsigned num_calls =
 		static_cast<unsigned>(syscall::MAX);
 
-	for (unsigned i = 0; i < num_calls; ++i) {
-		syscall_registry[i] = reinterpret_cast<uintptr_t>(syscall_invalid);
-		syscall_names[i] = nullptr;
-	}
+	kutil::memset(&syscall_registry, 0, sizeof(syscall_registry));
+	kutil::memset(&syscall_names, 0, sizeof(syscall_names));
 
 #define SYSCALL(id, name, result, ...) \
 	syscall_registry[id] = reinterpret_cast<uintptr_t>(syscalls::name); \
 	syscall_names[id] = #name; \
-	static_assert( id <= num_calls, "Syscall " #name " has id > syscall::MAX" );
+	static_assert( id <= num_calls, "Syscall " #name " has id > syscall::MAX" ); \
+	log::debug(logs::syscall, "Enabling syscall 0x%02x as " #name , id);
 #include "syscalls.inc"
 #undef SYSCALL
 }
diff --git a/src/kernel/syscall.s b/src/kernel/syscall.s
index 82ac6ae..5fae6ea 100644
--- a/src/kernel/syscall.s
+++ b/src/kernel/syscall.s
@@ -34,12 +34,16 @@ syscall_handler_prelude:
 	cmp rax, MAX_SYSCALLS
 	jle .ok_syscall
 
+.bad_syscall:
 	mov rdi, rax
 	call syscall_invalid
 
 .ok_syscall:
 	lea r11, [rel syscall_registry]
 	mov r11, [r11 + rax * 8]
+	cmp r11, 0
+	je .bad_syscall
+
 	call r11
 
 	inc qword [rel __counter_syscall_sysret]