initial kernel

yak-kernel/CMakeLists.txt

@@ -0,0 +1,27 @@
+project(yak-kernel)
+
+set(CMAKE_C_FLAGS "
+    -ffreestanding       \
+    -fno-stack-protector \
+    -fno-stack-check     \
+    -fno-lto             \
+    -fno-pie             \
+    -fno-pic             \
+    -m64                 \
+    -march=x86-64        \
+    -mabi=sysv           \
+    -mno-80387           \
+    -mno-mmx             \
+    -mno-sse             \
+    -mno-sse2            \
+    -mno-red-zone        \
+    -mcmodel=kernel")
+set(CMAKE_EXE_LINKER_FLAGS "
+    -nostdlib               \
+    -static                 \
+    -z max-page-size=0x1000 \
+    -T ${CMAKE_CURRENT_SOURCE_DIR}/linker.lds")
+
+include_directories(../limine/include)
+
+add_executable(yak.elf main.c)

yak-kernel/linker.lds

@@ -0,0 +1,57 @@
+/* Tell the linker that we want an x86_64 ELF64 output file */
+OUTPUT_FORMAT(elf64-x86-64)
+OUTPUT_ARCH(i386:x86-64)
+
+/* We want the symbol _start to be our entry point */
+ENTRY(_start)
+
+/* Define the program headers we want so the bootloader gives us the right */
+/* MMU permissions */
+PHDRS
+{
+    text    PT_LOAD    FLAGS((1 << 0) | (1 << 2)) ; /* Execute + Read */
+    rodata  PT_LOAD    FLAGS((1 << 2)) ;            /* Read only */
+    data    PT_LOAD    FLAGS((1 << 1) | (1 << 2)) ; /* Write + Read */
+}
+
+SECTIONS
+{
+    /* We wanna be placed in the topmost 2GiB of the address space, for optimisations */
+    /* and because that is what the Limine spec mandates. */
+    /* Any address in this region will do, but often 0xffffffff80000000 is chosen as */
+    /* that is the beginning of the region. */
+    . = 0xffffffff80000000;
+
+    .text : {
+        *(.text .text.*)
+    } :text
+
+    /* Move to the next memory page for .rodata */
+    . += CONSTANT(MAXPAGESIZE);
+
+    .rodata : {
+        *(.rodata .rodata.*)
+    } :rodata
+
+    /* Move to the next memory page for .data */
+    . += CONSTANT(MAXPAGESIZE);
+
+    .data : {
+        *(.data .data.*)
+    } :data
+
+    /* NOTE: .bss needs to be the last thing mapped to :data, otherwise lots of */
+    /* unnecessary zeros will be written to the binary. */
+    /* If you need, for example, .init_array and .fini_array, those should be placed */
+    /* above this. */
+    .bss : {
+        *(COMMON)
+        *(.bss .bss.*)
+    } :data
+
+    /* Discard .note.* and .eh_frame since they may cause issues on some hosts. */
+    /DISCARD/ : {
+        *(.eh_frame)
+        *(.note .note.*)
+    }
+}

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();
+}