implement generic syscalls

CMakeLists.txt

@@ -1,7 +1,7 @@
 # See the end of this file for copyright and license terms.
 
 cmake_minimum_required(VERSION 3.0.0)
-project(neo VERSION 0.1.0 LANGUAGES C)
+project(neo VERSION 0.1.0 LANGUAGES C ASM)
 set(CMAKE_C_STANDARD 11)
 
 if(CMAKE_PROJECT_NAME STREQUAL PROJECT_NAME)

demo/main.c

@@ -1,9 +1,11 @@
 /** See the end of this file for copyright and license terms. */
 
 #include "neo.h"
+#include "neo/_unistd.h"
 
 int main(int argc, char **argv)
 {
+	_neo_sys_write(1, "hello, world\n", 14);
 	return 69;
 }
 

include/neo/_unistd.h

@@ -0,0 +1,24 @@
+/** See the end of this file for copyright and license terms. */
+
+#pragma once
+
+#include "neo.h"
+
+long _neo_syscall(long number, ...);
+
+isize _neo_sys_write(int fd, const void *buf, usize count);
+__attribute__((__noreturn__))
+void _neo_sys_exit(int status);
+
+/*
+ * This file is part of libneo.
+ * Copyright (c) 2021 Fefie <owo@fef.moe>.
+ *
+ * libneo is non-violent software: you may only use, redistribute,
+ * and/or modify it under the terms of the CNPLv6+ as found in
+ * the LICENSE file in the source code root directory or at
+ * <https://git.pixie.town/thufie/CNPL>.
+ *
+ * libneo comes with ABSOLUTELY NO WARRANTY, to the extent
+ * permitted by applicable law.  See the CNPLv6+ for details.
+ */

src/arch/x86_64/CMakeLists.txt

@@ -0,0 +1,3 @@
+target_sources(neo PRIVATE
+    arch/${TARGET_ARCH}/syscall_${TARGET_OS}.S
+)

src/arch/x86_64/syscall_linux.S

@@ -0,0 +1,46 @@
+/** See the end of this file for copyright and license terms. */
+
+.global _neo_syscall
+
+/*
+ * long _neo_syscall(long number, ...);
+ *
+ * We just want to get stuff working for now, therefore we don't care
+ * about efficiency and just always copy all 6 arguments to the
+ * respective registers and hope Linux just ignores them lmao
+ *
+ *   SysV ABI -> Linux syscall
+ * -----------------------------
+ *   1. %rdi  -> %rax (number)
+ *   2. %rsi  -> %rdi (arg1)
+ *   3. %rdx  -> %rsi (arg2)
+ *   4. %rcx  -> %rdx (arg3)
+ *   5. %r8   -> %r10 (arg4)
+ *   6. %r9   -> %r8  (arg5)
+ *   7. stack -> %r9  (arg6)
+ */
+_neo_syscall:
+	mov	%rdi,	%rax
+	mov	%rsi,	%rdi
+	mov	%rdx,	%rsi
+	mov	%rcx,	%rdx
+	mov	%r8,	%r10
+	mov	%r9,	%r8
+	mov	(%rsp),	%r9
+	syscall
+	ret	/* result is already in %rax */
+.size _neo_syscall,.-_neo_syscall
+.type _neo_syscall,function
+
+/*
+ * This file is part of libneo.
+ * Copyright (c) 2021 Fefie <owo@fef.moe>.
+ *
+ * libneo is non-violent software: you may only use, redistribute,
+ * and/or modify it under the terms of the CNPLv6+ as found in
+ * the LICENSE file in the source code root directory or at
+ * <https://git.pixie.town/thufie/CNPL>.
+ *
+ * libneo comes with ABSOLUTELY NO WARRANTY, to the extent
+ * permitted by applicable law.  See the CNPLv6+ for details.
+ */

src/unistd.c

@@ -0,0 +1,30 @@
+/** See the end of this file for copyright and license terms. */
+
+#include "neo.h"
+#include "neo/_unistd.h"
+
+/* TODO: get rid of hardcoded syscall numbers */
+
+isize _neo_sys_write(int fd, const void *buf, usize len)
+{
+	return _neo_syscall(1, fd, buf, len);
+}
+
+void _neo_sys_exit(int status)
+{
+	_neo_syscall(60, status);
+	while (1); /* should not be reached */
+}
+
+/*
+ * This file is part of libneo.
+ * Copyright (c) 2021 Fefie <owo@fef.moe>.
+ *
+ * libneo is non-violent software: you may only use, redistribute,
+ * and/or modify it under the terms of the CNPLv6+ as found in
+ * the LICENSE file in the source code root directory or at
+ * <https://git.pixie.town/thufie/CNPL>.
+ *
+ * libneo comes with ABSOLUTELY NO WARRANTY, to the extent
+ * permitted by applicable law.  See the CNPLv6+ for details.
+ */