From 1e2bf71bb692cc6f622f4c57181d0dd87eb66f7c Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Sun, 21 Dec 2025 17:20:10 -0500
Subject: mos: Add initial C entrypoint

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 mos/sys/Makefile                 |  6 +++++-
 mos/sys/arch/x86_64/cpu/locore.S |  4 ++++
 mos/sys/kern/Makefile            | 16 ++++++++++++++++
 mos/sys/kern/kern_init.c         | 12 ++++++++++++
 4 files changed, 37 insertions(+), 1 deletion(-)
 create mode 100644 mos/sys/kern/Makefile
 create mode 100644 mos/sys/kern/kern_init.c

diff --git a/mos/sys/Makefile b/mos/sys/Makefile
index 59b4a84..47f70b7 100644
--- a/mos/sys/Makefile
+++ b/mos/sys/Makefile
@@ -10,7 +10,11 @@ SYS_CFLAGS =
 ARCH =
 
 .PHONY: all
-all: arch
+all: kern arch
+
+.PHONY: kern
+kern:
+	cd kern/; make CC=$(CC) LD=$(LD) SYS_CFLAGS="$(SYS_CFLAGS)"
 
 .PHONY: arch
 arch:
diff --git a/mos/sys/arch/x86_64/cpu/locore.S b/mos/sys/arch/x86_64/cpu/locore.S
index c8ffc4c..d96170b 100644
--- a/mos/sys/arch/x86_64/cpu/locore.S
+++ b/mos/sys/arch/x86_64/cpu/locore.S
@@ -5,10 +5,14 @@
 
     .text
     .globl _start
+    .globl kern_main
 _start:
     cli
     cld
 
+    xor %rbp, %rbp      /* Terminate callstack */
+    call kern_main      /* Call kernel main */
+
 1:  cli
     hlt
     jmp 1b
diff --git a/mos/sys/kern/Makefile b/mos/sys/kern/Makefile
new file mode 100644
index 0000000..1ee87c2
--- /dev/null
+++ b/mos/sys/kern/Makefile
@@ -0,0 +1,16 @@
+#
+# Copyright (c) 2025, Ian Moffett.
+# Provided under the BSD-3 clause.
+#
+
+CFILES = $(shell find . -name "*.c")
+OFILES = $(CFILES:.c=.o)
+
+SYS_CFLAGS =
+CFLAGS = $(SYS_CFLAGS) -I../../../usr/sdk/inc/
+
+.PHONY: all
+all: $(OFILES)
+
+%.o: %.c
+	$(CC) -c $(CFLAGS) $< -o $@
diff --git a/mos/sys/kern/kern_init.c b/mos/sys/kern/kern_init.c
new file mode 100644
index 0000000..62d73fb
--- /dev/null
+++ b/mos/sys/kern/kern_init.c
@@ -0,0 +1,12 @@
+/*
+ * Copyright (c) 2025, Ian Moffett.
+ * Provided under the BSD-3 clause.
+ */
+
+/* Forward declaration */
+void kern_main(void);
+
+void
+kern_main(void)
+{
+}
-- 
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