diff options
Diffstat (limited to 'libc/sysdeps/linux/x86_64/crt0.S')
| -rw-r--r-- | libc/sysdeps/linux/x86_64/crt0.S | 164 |
1 files changed, 164 insertions, 0 deletions
diff --git a/libc/sysdeps/linux/x86_64/crt0.S b/libc/sysdeps/linux/x86_64/crt0.S new file mode 100644 index 000000000..82dd9a9df --- /dev/null +++ b/libc/sysdeps/linux/x86_64/crt0.S @@ -0,0 +1,164 @@ +/* Startup code compliant to the ELF x86-64 ABI. + Copyright (C) 2001, 2002, 2003 Free Software Foundation, Inc. + This file is part of the GNU C Library. + Contributed by Andreas Jaeger <aj@suse.de>, 2001. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + In addition to the permissions in the GNU Lesser General Public + License, the Free Software Foundation gives you unlimited + permission to link the compiled version of this file with other + programs, and to distribute those programs without any restriction + coming from the use of this file. (The GNU Lesser General Public + License restrictions do apply in other respects; for example, they + cover modification of the file, and distribution when not linked + into another program.) + + Note that people who make modified versions of this file are not + obligated to grant this special exception for their modified + versions; it is their choice whether to do so. The GNU Lesser + General Public License gives permission to release a modified + version without this exception; this exception also makes it + possible to release a modified version which carries forward this + exception. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA + 02111-1307 USA. */ + +/* Originally based on glibc's sysdeps/x86_64/elf/start.S */ + +/* This is the canonical entry point, usually the first thing in the text + segment. The SVR4/i386 ABI (pages 3-31, 3-32) says that when the entry + point runs, most registers' values are unspecified, except for: + + %rdx Contains a function pointer to be registered with `atexit'. + This is how the dynamic linker arranges to have DT_FINI + functions called for shared libraries that have been loaded + before this code runs. + + %rsp The stack contains the arguments and environment: + 0(%rsp) argc + 8(%rsp) argv[0] + ... + (8*argc)(%rsp) NULL + (8*(argc+1))(%rsp) envp[0] + ... + NULL +*/ + +#include <features.h> + +.text + .global _start + .type _start,%function +#if defined L_crt0 || defined L_Scrt0 || ! defined __UCLIBC_CTOR_DTOR__ + .type __uClibc_main,%function +#else + .weak _init + .weak _fini + .type __uClibc_start_main,%function +#endif +/* Stick in a dummy reference to main(), so that if an application + * is linking when the main() function is in a static library (.a) + * we can be sure that main() actually gets linked in */ + .type main,%function + +_start: + /* Clear the frame pointer. The ABI suggests this be done, to mark + the outermost frame obviously. */ + xorq %rbp, %rbp + + /* Extract the arguments as encoded on the stack and set up + the arguments for __libc_start_main (int (*main) (int, char **, char **), + int argc, char *argv, + void (*init) (void), void (*fini) (void), + void (*rtld_fini) (void), void *stack_end). + The arguments are passed via registers and on the stack: + main: %rdi + argc: %rsi + argv: %rdx + init: %rcx + fini: %r8 + rtld_fini: %r9 + stack_end: stack. */ + + movq %rdx, %r9 /* Address of the shared library termination function. */ + popq %rsi /* Pop the argument count. */ + movq %rsp, %rdx /* argv starts just at the current stack top. */ + movq %rsi, %rbx /* now we calc envp ... envp = argc */ + shl $0x3, %rbx /* envp *= 8 */ + addq %rdx, %rbx /* envp += argv */ + /* Align the stack to a 16 byte boundary to follow the ABI. */ + andq $~15, %rsp + + pushq %rax /* Push garbage because we push 8 more bytes. */ + + /* Provide the highest stack address to the user code (for stacks + which grow downwards). */ + pushq %rsp + +/************** + * START TODO */ +#if defined L_Scrt0 || defined L_Scrt1 + call .L0 +.L0: + popq %rbx + addq $_GLOBAL_OFFSET_TABLE_+[.-.L0],%rbx +#endif + +#if (defined L_crt1 || defined L_Scrt1) && defined __UCLIBC_CTOR_DTOR__ + /* Push .init and .fini arguments to __uClibc_start_main() on the stack */ +#ifdef L_Scrt1 + pushl _fini@GOT(%rip) + pushl _init@GOT(%rip) +#else + pushl $_fini + pushl $_init +#endif + + /* Push envp, argc, and argc arguments to __uClibc_start_main() on the stack */ + pushq %rbx /* Environment pointer */ + pushq %rdx /* Argument pointer */ + pushq %rsi /* And the argument count */ + + /* Ok, now run uClibc's main() -- shouldn't return */ +#ifdef L_Scrt1 + call *__uClibc_start_main@GOT(%rip) +#else + call __uClibc_start_main +#endif +#else + /* Push envp, argc, and argc arguments to __uClibc_start_main() on the stack */ + pushq %rbx /* Environment pointer */ + pushq %rdx /* Argument pointer */ + pushq %rsi /* And the argument count */ + +#ifdef L_Scrt0 + call *__uClibc_main@GOT(%rip) +#else + call __uClibc_main +#endif +#endif +/* END TODO * + ************/ + + hlt /* Crash if somehow `exit' does return. */ +.size _start,.-_start + +/* Define a symbol for the first piece of initialized data. */ + .data + .globl __data_start +__data_start: + .long 0 + .weak data_start + data_start = __data_start |