add simple sum example

examples/linker.ld

@@ -0,0 +1,70 @@
+/* Kernel entry function */
+ENTRY(_start)
+
+OUTPUT_FORMAT(elf32-i386)
+
+SECTIONS {
+
+    /DISCARD/ : {
+        *(".text.inlined*")
+        *(.comment)
+        *(.eh_frame)
+        *(.note.gnu.build-id)
+    }
+
+    /* Set kernel start address */
+    . = 0x100000;
+
+    /* Code and readonly data */
+    .text : {
+        /* fill gaps with int3 opcode to detect invalid jumps */
+        FILL(0xcc)
+
+        /* multiboot header */
+        multiboot_header = .;
+        KEEP (*(".rodata.multiboot"))
+
+        /* /\* fixed address for IRQ handlers *\/ */
+        /* . = 0x1000; */
+
+        /* /\* start of interrupt handlers *\/ */
+        /* _stext_irqs = .; */
+
+        /* /\* IRQ Handlers *\/ */
+        /* KEEP (*(".text.irqhandlers*")) /\* ASM *\/ */
+        /* KEEP (*(".text.irq_handler*")) /\* C *\/ */
+        /* *(".text.isrs*") /\* C *\/ */
+        /* *(".text.isr_*") /\* C *\/ */
+        /* KEEP (*(".text.OSEKOS_ISR*")) */
+        /* KEEP (*(".text.idt")) /\* ASM *\/ */
+
+        /* /\* sysenter handler *\/ */
+        /* KEEP (*(".text.sysenter_syscall")) */
+
+        /* _etext_irqs = .; */
+        /* . += 16; /\* padding after data, workaround for import-trace *\/ */
+
+        KEEP (*(".text.startup"))
+        *(".text*")
+        *(".rodata*")
+    }
+
+    /* Data and Stacks */
+    . = 0x200000;
+    .data : {
+        KEEP (*(".startup_stack"))
+        KEEP (*(".kernel_stack"))
+        *(".data*")
+        *(COMMON);
+    }
+
+    /* Memory-mapped I/O APIC */
+    _sioapic = 0xFEC00000;
+    ioapic = 0xFEC00000;
+    _eioapic = 0xFEC00FFF;
+
+    /* Memory-mapped Local APIC */
+    _slapic = 0xFEE00000;
+    lapic = 0xFEE00000;
+    _elapic = 0xFEE00FFF;
+}