Hello, world! in linear framebuffer

Makefile

@@ -1,6 +1,7 @@
 build:
 	rm -f *.o
-	x86_64-elf-gcc -c -I src src/kmain.c -Wall -Wextra -std=gnu99 -nostdlib -ffreestanding -fno-stack-protector -fno-stack-check -fno-PIC -ffunction-sections -fdata-sections
+	x86_64-elf-gcc -c -I src src/term.c src/kmain.c -Wall -Wextra -std=gnu99 -nostdlib -ffreestanding -fno-stack-protector -fno-stack-check -fno-PIC -ffunction-sections -fdata-sections -mcmodel=kernel
+	objcopy -O elf64-x86-64 -B i386 -I binary zap-light16.psf zap-light16.o
 	x86_64-elf-ld -o kernel -T linker.ld *.o
 
 limine/limine:
@@ -25,5 +26,8 @@ build-iso: limine/limine build
 		iso_root -o kernel.iso
 	./limine/limine bios-install kernel.iso
 
+run:
+	qemu-system-x86_64 -cdrom kernel.iso
+
 clean:
 	rm -rf *.o kernel iso_root kernel.iso limine

README.md

@@ -9,3 +9,10 @@ make build-iso
 ```
 
 Then it can be run with `qemu-system-x86_64 kernel.iso`.
+
+
+### Kernel conventions
+
+Functions that return an integer as status of success/failure will return:
+- 0 if everything went correctly
+- a negative value if something went wrong

src/kernel.h

@@ -0,0 +1,9 @@
+#ifndef KERNEL_H
+#define KERNEL_H
+
+enum ErrorCodes
+{
+	ENOMEM
+};
+
+#endif

src/kmain.c

@@ -1,6 +1,7 @@
 #include <stdbool.h>
 #include <stddef.h>
 #include <limine.h>
+#include "term.h"
 
 // Limine version used
 __attribute__((used, section(".limine_requests")))
@@ -19,6 +20,8 @@ static volatile LIMINE_REQUESTS_START_MARKER;
 __attribute__((used, section(".limine_requests_end")))
 static volatile LIMINE_REQUESTS_END_MARKER;
 
+struct limine_framebuffer* framebuffer;
+
 // We won't be linked to standard library, but still need the basic mem* functions
 // so everything goes allright with the compiler
 
@@ -103,14 +106,12 @@ void kmain()
 	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];
+	framebuffer = framebuffer_request.response->framebuffers[0];
+
+	if (term_init()) hcf();
 
 	// Draw something
-	for (size_t i=0; i<100; i++)
+	kputs("Hello, world!");
-	{
-		volatile uint32_t* fb_ptr = framebuffer->address;
-		fb_ptr[i*(framebuffer->pitch/4) + i] = 0xffffff;
-	}
 
 	hcf();
 }

src/term.c

@@ -0,0 +1,99 @@
+// Terminal output
+
+#include <limine.h>
+#include <stddef.h>
+#include "kernel.h"
+#include "term.h"
+
+extern struct limine_framebuffer* framebuffer;
+
+// Importing the PSF object file
+extern unsigned char _binary_zap_light16_psf_start[];
+extern unsigned char _binary_zap_light16_psf_end[];
+
+PSF1_Header* font = (PSF1_Header*)_binary_zap_light16_psf_start;
+uint8_t* glyphs = _binary_zap_light16_psf_start + sizeof(PSF1_Header);
+
+#define FONT_WIDTH 8
+#define FONT_HEIGHT font->characterSize
+
+// Character cursor
+typedef struct
+{
+	unsigned int x;
+	unsigned int y;
+} Cursor;
+
+Cursor cursor = {0};
+
+unsigned char* fb;
+
+int term_init()
+{
+	// Get framebuffer address from Limine struct
+	
+	if (framebuffer)
+	{
+		fb = framebuffer->address;
+		return 0;
+	}
+	return -ENOMEM;
+}
+
+// These are marked "static" because we don't wanna expose them all around
+// AKA they should just be seen here (kind of like private functions in cpp)
+static void putpixel(int x, int y, int color)
+{
+	// Depth isn't part of limine_framebuffer attributes so it will be 4
+	unsigned pos = x*4 + y*framebuffer->pitch;
+	fb[pos] = color & 255; // blue channel
+	fb[pos+1] = (color >> 8) & 255; // green
+	fb[pos+2] = (color >> 16) & 255; // blue
+}
+
+static void draw_char(char c, int px, int py, int fg, int bg)
+{
+	uint8_t* glyph = glyphs + ((unsigned char)c * FONT_HEIGHT);
+
+	for (size_t y=0; y<FONT_HEIGHT; y++)
+	{
+		uint8_t row = glyph[y];
+		for (size_t x=0; x<8; x++)
+		{
+			int color = (row & (0x80 >> x)) ? fg : bg;
+			putpixel(px+x, py+y, color);
+		}
+	}
+}
+
+static void putchar(char c)
+{
+	if (c == '\n')
+	{
+		cursor.x = 0;
+		cursor.y++;
+		return;
+	}
+
+	if ((cursor.x+1)*FONT_WIDTH >= framebuffer->width)
+	{
+		cursor.x = 0;
+		cursor.y++;
+	}
+
+	int px = cursor.x * FONT_WIDTH;
+	int py = cursor.y * FONT_HEIGHT;
+	draw_char(c, px, py, WHITE, BLACK);
+	cursor.x++;
+}
+
+// Debug-printing
+void kputs(const char* str)
+{
+	unsigned int i=0;
+	while (str[i] != 0)
+	{
+		putchar(str[i]);
+		i++;
+	}
+}

src/term.h

@@ -0,0 +1,22 @@
+#ifndef TERM_H
+#define TERM_H
+
+int term_init();
+void kputs(const char* str);
+
+enum TermColors
+{
+    BLACK = 0x000000,
+    WHITE = 0xffffff
+};
+
+#define PSF1_FONT_MAGIC 0x0436
+
+typedef struct
+{
+    uint16_t magic;
+    uint8_t fontMode;
+    uint8_t characterSize; // height
+} PSF1_Header;
+
+#endif