initial kernel

yak-kernel/main.c

@@ -0,0 +1,107 @@
+#include <stdint.h>
+#include <stddef.h>
+#include <limine.h>
+
+// The Limine requests can be placed anywhere, but it is important that
+// the compiler does not optimise them away, so, usually, they should
+// be made volatile or equivalent.
+
+static volatile struct limine_terminal_request terminal_request = {
+        .id = LIMINE_TERMINAL_REQUEST,
+        .revision = 0
+};
+
+// GCC and Clang reserve the right to generate calls to the following
+// 4 functions even if they are not directly called.
+// Implement them as the C specification mandates.
+// DO NOT remove or rename these functions, or stuff will eventually break!
+// They CAN be moved to a different .c file.
+
+void *memcpy(void *dest, const void *src, size_t n) {
+    uint8_t *pdest = (uint8_t *) dest;
+    const uint8_t *psrc = (const uint8_t *) src;
+
+    for (size_t i = 0; i < n; i++) {
+        pdest[i] = psrc[i];
+    }
+
+    return dest;
+}
+
+void *memset(void *s, int c, size_t n) {
+    uint8_t *p = (uint8_t *) s;
+
+    for (size_t i = 0; i < n; i++) {
+        p[i] = (uint8_t) c;
+    }
+
+    return s;
+}
+
+void *memmove(void *dest, const void *src, size_t n) {
+    uint8_t *pdest = (uint8_t *) dest;
+    const uint8_t *psrc = (const uint8_t *) src;
+
+    if (src > dest) {
+        for (size_t i = 0; i < n; i++) {
+            pdest[i] = psrc[i];
+        }
+    } else if (src < dest) {
+        for (size_t i = n; i > 0; i--) {
+            pdest[i - 1] = psrc[i - 1];
+        }
+    }
+
+    return dest;
+}
+
+int memcmp(const void *s1, const void *s2, size_t n) {
+    const uint8_t *p1 = (const uint8_t *) s1;
+    const uint8_t *p2 = (const uint8_t *) s2;
+
+    for (size_t i = 0; i < n; i++) {
+        if (p1[i] != p2[i]) {
+            return p1[i] < p2[i] ? -1 : 1;
+        }
+    }
+
+    return 0;
+}
+
+// Our quick and dirty strlen() implementation.
+size_t strlen(const char *str) {
+    size_t ret = 0;
+    while (*str++) {
+        ret++;
+    }
+    return ret;
+}
+
+// Halt and catch fire function.
+static void hcf(void) {
+    __asm__ ("cli");
+    for (;;) {
+        __asm__ ("hlt");
+    }
+}
+
+// The following will be our kernel's entry point.
+// If renaming _start() to something else, make sure to change the
+// linker script accordingly.
+void _start(void) {
+    // Ensure we got a terminal
+    if (terminal_request.response == NULL
+        || terminal_request.response->terminal_count < 1) {
+        hcf();
+    }
+
+    // We should now be able to call the Limine terminal to print out
+    // a simple "Hello World" to screen.
+    const char *hello_msg = "Hello World";
+
+    struct limine_terminal *terminal = terminal_request.response->terminals[0];
+    terminal_request.response->write(terminal, hello_msg, strlen(hello_msg));
+
+    // We're done, just hang...
+    hcf();
+}