First steps: include Limine, kernel entry point, framebuffer request

src/kmain.c

@@ -0,0 +1,116 @@
+#include <stdbool.h>
+#include <stddef.h>
+#include <limine.h>
+
+// Limine version used
+__attribute__((used, section(".limine_requests")))
+static volatile LIMINE_BASE_REVISION(3);
+
+// Framebuffer request
+__attribute__((used, section(".limine_requests")))
+static volatile struct limine_framebuffer_request framebuffer_request = {
+	.id = LIMINE_FRAMEBUFFER_REQUEST,
+	.revision = 0
+};
+
+__attribute__((used, section(".limine_requests_start")))
+static volatile LIMINE_REQUESTS_START_MARKER;
+
+__attribute__((used, section(".limine_requests_end")))
+static volatile LIMINE_REQUESTS_END_MARKER;
+
+// We won't be linked to standard library, but still need the basic mem* functions
+// so everything goes allright with the compiler
+
+// We use the "restrict" keyword on pointers so that the compiler knows it can
+// do more optimization on them (and as it's a much used function, it's good to
+// be able to do that)
+void* memcpy(void* restrict dest, const void* restrict src, size_t n)
+{
+	uint8_t* restrict pdest = (uint8_t* restrict)dest;
+	const uint8_t* restrict psrc = (const uint8_t* restrict)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 = (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;
+}
+
+// Panic 
+static void hcf()
+{
+	for (;;)
+	{
+		asm("hlt");
+	}
+}
+
+// This is our entry point
+void kmain()
+{
+	if (!LIMINE_BASE_REVISION_SUPPORTED) hcf();
+	if (framebuffer_request.response == NULL || framebuffer_request.response->framebuffer_count < 1) hcf();
+
+	// Get the first framebuffer from the response
+	struct limine_framebuffer* framebuffer = framebuffer_request.response->framebuffers[0];
+
+	// Draw something
+	for (size_t i=0; i<100; i++)
+	{
+		volatile uint32_t* fb_ptr = framebuffer->address;
+		fb_ptr[i*(framebuffer->pitch/4) + i] = 0xffffff;
+	}
+
+	hcf();
+}