dl-startup.h

ucLinux is a very good embeded sytem. Most of company use this as their development OS.

/* vi: set sw=4 ts=4: */
/*
 * Architecture specific code used by dl-startup.c
 * Copyright (C) 2000-2005 by Erik Andersen <[e-mail]>
 * Copyright (C) 2005 by Mike Frysinger <[e-mail]>
 *
 * Parts taken from glibc/sysdeps/x86_64/dl-machine.h
 */
asm(
	"	.text\n"
	"	.align 16\n"
	"	.global _start\n"
	"	.type   _start,%function\n"
	"_start:\n"
	"	movq %rsp, %rdi\n"
	"	call _dl_start\n"
	"	# Save the user entry point address in %r12.\n"
	"	movq %rax, %r12\n"
	"	# See if we were run as a command with the executable file\n"
	"	# name as an extra leading argument.\n"
	"	movl _dl_skip_args(%rip), %eax\n"
	"	# Pop the original argument count.\n"
	"	popq %rdx\n"
	"	# Adjust the stack pointer to skip _dl_skip_args words.\n"
	"	leaq (%rsp,%rax,8), %rsp\n"
	"	# Subtract _dl_skip_args from argc.\n"
	"	subl %eax, %edx\n"
	"	# Push argc back on the stack.\n"
	"	pushq %rdx\n"
	"	# Pass our finalizer function to the user in %rdx, as per ELF ABI.\n"
	"	leaq _dl_fini(%rip), %rdx\n"
	"	# Jump to the user's entry point.\n"
	"	jmp *%r12\n"
	"	.size	_start,.-_start\n"
	"	.previous\n"
);

/* Get a pointer to the argv array.  On many platforms this can be just
 * the address if the first argument, on other platforms we need to
 * do something a little more subtle here.  */
#define GET_ARGV(ARGVP, ARGS) ARGVP = (((unsigned long*) ARGS)+1)

/* Handle relocation of the symbols in the dynamic loader. */
static __always_inline
void PERFORM_BOOTSTRAP_RELOC(ELF_RELOC *rpnt, unsigned long *reloc_addr,
	unsigned long symbol_addr, unsigned long load_addr, Elf64_Sym *sym)
{
	switch (ELF64_R_TYPE(rpnt->r_info)) {
		case R_X86_64_GLOB_DAT:
		case R_X86_64_JUMP_SLOT:
			*reloc_addr = symbol_addr + rpnt->r_addend;
			break;
		case R_X86_64_DTPMOD64:
			*reloc_addr = 1;
			break;
		case R_X86_64_NONE:
		case R_X86_64_DTPOFF64:
			break;
		case R_X86_64_TPOFF64:
			*reloc_addr = sym->st_value + rpnt->r_addend - symbol_addr;
			break;
		default:
			_dl_exit(1);
	}
}

/* Transfer control to the user's application, once the dynamic loader is
 * done.  This routine has to exit the current function, then call the
 * _dl_elf_main function.  */
#define START() return _dl_elf_main