Why does an assembly program only work when linked with crt1.o crti.o and crtn.o?

问题

I like to know how programs work so to make it as bare bones as possible I fool around with assembly.

I just found out how to assemble code for x86_64 using wprintf function (found out wide chars are 32 bit). all I had to do was link to libc (-lc).

I'm trying to assemble code for 32-bit doing about the same thing but I stumbled quite a bit. Eventually I used gcc to do the linking ( and changed the _start: to main:). So then I did the linking myself using ld and included crt1.o crti.o and crtn.o. Then my program worked ( it wouldn't print out anything before ) So my question is, can I do something within my code to eliminate the need for these other 3 object files (and of course revert back to _start: instead of main:)?

test_lib.S

.section .data
locale:
  .string ""
  .align 4
printformat:
  .long '%','l','c',0

.section .text
.global main
main:

pushl   $locale
pushl   $6
call    setlocale
pushl   $12414
pushl   $printformat
call    wprintf
pushl   $2
call    exit

and running the following

as --32 test_lib.S -o test_lib.o
ld -m elf_i386 -L/lib/ -L/usr/lib/ -I/lib/ld-linux.so.2 /usr/lib/crt1.o /usr/lib/crti.o -lc /usr/lib/crtn.o test_lib.o -o test_lib
./test_lib

oh and the output is simply a japanese hiragana (ma)ま (notice there is no line break so it prints before the prompt)

回答1:

Here are what the files do for you. They are the c-runtime environment and setup that link to the OS.

crt1.o Newer style of the initial runtime code. Contains the _start symbol which sets up the env with argc/argv/libc _init/libc _fini before jumping to the libc main. glibc calls this file 'start.S'.
crti.o Defines the function prolog; _init in the .init section and _fini in the .fini section. glibc calls this 'initfini.c'.
crtn.o Defines the function epilog. glibc calls this 'initfini.c'.

There is an excellent write up and example code to be found at the following website http://wiki.osdev.org/Creating_a_C_Library for each of the libraries above.

回答2:

In 3-bit Linux, they're on the stack. At start up, 0(%esp) contains argc. At 4(%esp), you'll find a pointer to the program name (which is included in argc). After that comes an array of pointers to the arguments, concluded with a NULL pointer. After that comes another NULL-concluded array of pointers to system variables. I am told that there may be over 200 of them!!

Shiarta

来源：https://stackoverflow.com/questions/18091463/why-does-an-assembly-program-only-work-when-linked-with-crt1-o-crti-o-and-crtn-o

标签

assembly

linker

x86

32-bit