Bootstrap the project

For now the base layout has been defined and we have a binary that is
properly reached through openSBI.

Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>

1 files changed, 52 insertions, 0 deletions

diff --git a/kernel/fbos.ld.S b/kernel/fbos.ld.S
new file mode 100644
index 0000000..f288161
--- /dev/null
+++ b/kernel/fbos.ld.S
@@ -0,0 +1,52 @@
+#include <fbos/mm.h>
+
+SECTIONS {
+	// Ensure that the image starts at the very exact address SBI expects it to.
+	. = LINK_ADDR;
+
+	// You would usually want to separate the head section into its own thing
+	// instead of clumping it into the main `.text` one. Well, I'm no expert on
+	// linker configuration, so patches are welcome :)
+	.text : {
+		// The very first thing has to be the `_start` function, which is where
+		// SBI will jump into. Afterwards comes the rest of `.text.head`.
+		_start = .;
+		*(.text.head)
+
+		// Aligning it to a full page is maybe a bit too much considering how
+		// small `.text.head` really is. I just saw this same thing on the Linux
+		// Kernel and it felt clean.
+		. = ALIGN(PAGE_SIZE);
+
+		// From now on the rest of the `.text` could just be a continuation, but
+		// I further split it into `.text.kernel` so the jump from head isn't
+		// that large. That is, we put first the very core of the kernel, and
+		// the rest can go wherever.
+		__kernel_text_start = .;
+		*(.text.kernel)
+		__kernel_text_end = .;
+
+		// And the rest.
+    	*(.text)
+	}
+
+	// In total we would reserve two full blown pages for the kernel code, which
+	// is definitely too much, but whatever, memory is cheap.
+	. = ALIGN(PAGE_SIZE);
+
+	.data : {
+    	*(.data)
+	}
+
+	. = ALIGN(8);
+
+	.rodata : {
+    	*(.rodata)
+	}
+
+	. = ALIGN(8);
+
+	.bss : {
+    	*(.bss)
+	}
+}