Handout

kernel/compiler/libc.cc

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+#include "libc.h"
+
+/*! \brief Function pointer for initialization/finalization functions for global
+ * objects required since GCC 4.7 and later.
+ *
+ * These symbols appear kind of magically due to the compiler
+ */
+extern void (*__preinit_array_start[])();
+extern void (*__preinit_array_end[])();
+extern void (*__init_array_start[])();
+extern void (*__init_array_end[])();
+extern void (*__fini_array_start[])();
+extern void (*__fini_array_end[])();
+
+namespace CSU {
+
+void initializer() {
+	const unsigned int preinit_size =
+		__preinit_array_end - __preinit_array_start;
+	for (unsigned int i = 0; i != preinit_size; ++i) {
+		(*__preinit_array_start[i])();
+	}
+
+	const size_t size = __init_array_end - __init_array_start;
+	for (size_t i = 0; i < size; i++) {
+		(*__init_array_start[i])();
+	}
+}
+
+void finalizer() {
+	const unsigned int fini_size = __fini_array_end - __fini_array_start;
+	for (unsigned int i = 0; i != fini_size; ++i) {
+		(*__fini_array_start[i])();
+	}
+}
+
+}  // namespace CSU
+
+extern "C" int atexit(void (*func)(void)) {
+	// Registers a function that will be executed on exit.
+	// We simply ignore those functions, as we don't need them for our operating
+	// systems.
+	(void)func;
+
+	return 0;
+}

kernel/compiler/libc.h

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+/*! \file
+ *  \brief Initialization functions for global objects required by the compiler
+ */
+
+#pragma once
+#include "types.h"
+
+/*! \brief C StartUp (CSU)
+ * required by the compiler and provided by the c standard library
+ */
+namespace CSU {
+
+/*! \brief Call global constructors and initialization functions
+ * (this is usually done by __libc_csu_init)
+ */
+void initializer();
+
+/*! \brief Call global destructors and finalizer functions
+ * (this is usually done by __libc_csu_fini)
+ */
+void finalizer();
+
+}  // namespace CSU

kernel/compiler/libcxx.cc

@@ -0,0 +1,33 @@
+/*! \file
+ *  \brief C++ runtime support functions
+ */
+
+#include "../debug/assert.h"
+#include "../types.h"
+
+void* operator new([[maybe_unused]] size_t size, void* place) { return place; }
+
+void* operator new(size_t size) {
+	(void)size;
+	assert(!"Memory allocation not supported");
+}
+
+void* operator new[](size_t size) {
+	(void)size;
+	assert(!"Memory allocation not supported");
+}
+
+void operator delete(void* ptr) { (void)ptr; }
+void operator delete(void* ptr, [[maybe_unused]] size_t size) {
+	operator delete(ptr);
+}
+
+void operator delete[](void* ptr) { operator delete(ptr); }
+void operator delete[](void* ptr, size_t size) { operator delete(ptr, size); }
+
+extern "C" [[noreturn]] void __cxa_pure_virtual() {
+	// Pure virtual function was called -- this if obviously not valid,
+	// therefore we wait infinitely.
+	while (true) {
+	}
+}

kernel/compiler/sections.ld

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+/* Entry in our OS -- label 'startup_bsp' in file boot/startup.asm */
+ENTRY(startup_bsp)
+
+SECTIONS
+ {
+	/* start address of our kernel */
+	. = 16M;
+
+	___KERNEL_START___ = .;
+
+	.boot :
+	{
+		/* Multiboot Header should be at the very beginning */
+		*(.multiboot_header)
+	}
+
+
+	.text :
+	{
+		*(".text")
+		*(".text$")
+		*(".init")
+		*(".fini")
+		*(".gnu.linkonce.*")
+		KEEP(*(.note.gnu.build-id))
+	}
+
+	/* lists containing the start address of global constructors and destructors (generated by the compiler) */
+	.preinit_array :
+	{
+		PROVIDE_HIDDEN (__preinit_array_start = .);
+		KEEP (*(.preinit_array))
+		PROVIDE_HIDDEN (__preinit_array_end = .);
+	}
+	.init_array :
+	{
+		PROVIDE_HIDDEN (__init_array_start = .);
+		KEEP (*(SORT(.init_array.*)))
+		KEEP (*(.init_array))
+		PROVIDE_HIDDEN (__init_array_end = .);
+	}
+	.fini_array :
+	{
+		PROVIDE_HIDDEN (__fini_array_start = .);
+		KEEP (*(SORT(.fini_array.*)))
+		KEEP (*(.fini_array))
+		PROVIDE_HIDDEN (__fini_array_end = .);
+	}
+
+
+	.data :
+	{
+		*(".data")
+		*(".data$")
+		*(".rodata")
+		___CTOR_LIST__ = .;
+		*(".ctors")
+		*(".ctor")
+		___CTOR_LIST_END__ = .;
+		___DTOR_LIST__ = .;
+		*(".dtors")
+		*(".dtor")
+		___DTOR_LIST_END__ = .;
+		*(".got")
+		*(".got.plt")
+		*(".eh_frame")
+		*(".eh_fram")
+		*(".jcr")
+	}
+
+	/* Start for application processors, relocated by APIC::init()
+	 * to a below 1 MB address to boot from real mode.
+	 * It is possible to let the linker place it at a below 1 MB address,
+	 * while all the rest starts at 16 MB. This will work for multiboot
+	 * compliant boot loader like GRUB and PXELINUX, however,
+	 * the qemu boot loader cannot handle such ELF files (yet)...
+	 * That's why we have to do it in our software */
+	.setup_ap_seg ALIGN(0x10) :
+	{
+		___SETUP_AP_START__ = .;
+		*(".setup_ap_seg")
+		*(".setup_ap_seg$")
+	}
+	___SETUP_AP_END__ = .;
+
+	.bss :
+	{
+		*(".bss")
+		*(".bss.*")
+		*(COMMON)
+	}
+	___KERNEL_END___ = .;
+
+
+	/DISCARD/ :
+	{
+		*(".note")
+		*(".comment")
+/* Keep debug information
+		*(".debug_line")
+		*(".debug_info")
+		*(".debug_abbrev")
+		*(".debug_aranges")
+*/
+	}
+ }