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/* 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
*/
.text
.globl _start
.type _start,@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 operatingsystem_parameter_argc@GOTPCREL(%rip),%rax
movq %rsi,(%rax)
movq operatingsystem_parameter_argv@GOTPCREL(%rip),%rax
movq %rsp,(%rax) /* argv starts just at the current stack top. */
leaq 8(,%rsi,8),%rax
addq %rsp,%rax
movq operatingsystem_parameter_envp@GOTPCREL(%rip),%rsi
movq %rax,(%rsi)
/* 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
/* Pass address of our own entry points to .fini and .init. */
movq _init_dummy@GOTPCREL(%rip), %rcx
movq _fini_dummy@GOTPCREL(%rip), %r8
movq main_stub@GOTPCREL(%rip), %rdi
/* Call the user's main function, and exit with its value.
But let the libc call main. */
call __libc_start_main@PLT
hlt /* Crash if somehow `exit' does return. */
/* fake main routine which will be run from libc */
.globl main_stub
.type main_stub,@function
main_stub:
/* save return address */
popq %rax
// stack alignment
pushq %rax
movq ___fpc_ret_rbp@GOTPCREL(%rip),%rcx
movq %rbp,(%rcx)
movq ___fpc_ret@GOTPCREL(%rip),%rcx
movq %rax,(%rcx)
pushq %rax
/* Save initial stackpointer */
movq __stkptr@GOTPCREL(%rip),%rax
movq %rsp,(%rax)
/* start the program */
xorq %rbp,%rbp
call PASCALMAIN@PLT
hlt
.size main_stub,.-main_stub
.globl _haltproc
.type _haltproc,@function
_haltproc:
movq operatingsystem_result@GOTPCREL(%rip),%rax
movzwl (%rax),%eax
/* return to libc */
movq ___fpc_ret_rbp@GOTPCREL(%rip),%rcx
movq (%rcx),%rbp
movq ___fpc_ret@GOTPCREL(%rip),%rcx
movq (%rcx),%rdx
pushq %rdx
ret
.size _haltproc,.-_haltproc
.globl _init_dummy
.type _init_dummy, @function
_init_dummy:
ret
.size _init_dummy,.-_init_dummy
.globl _fini_dummy
.type _fini_dummy, @function
_fini_dummy:
ret
.size _fini_dummy,.-_fini_dummy
/* 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
.globl ___fpc_brk_addr /* heap management */
.type ___fpc_brk_addr,@object
.size ___fpc_brk_addr,8
___fpc_brk_addr:
.quad 0
___fpc_ret: /* return address to libc */
.quad 0
___fpc_ret_rbp:
.quad 0
.bss
.comm __stkptr,8
.comm operatingsystem_parameter_envp,8
.comm operatingsystem_parameter_argc,8
.comm operatingsystem_parameter_argv,8
/* We need this stuff to make gdb behave itself, otherwise
gdb will chokes with SIGILL when trying to debug apps.
*/
.section ".note.ABI-tag", "a"
.align 4
.long 1f - 0f
.long 3f - 2f
.long 1
0: .asciz "GNU"
1: .align 4
2: .long 0
.long 2,4,0
3: .align 4
.section .note.GNU-stack,"",@progbits
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