x86 - assembly, segmentation fault -

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this code results in segmentation fault, have no idea why it, code supposed pass current location of esp @ stack ebp , use indirect addressing mode on ebp value of address, don't know why os terminating results in segmentation fault

.section .data .section .text .globl _start _start: movl $50,%edx pushl, %edx movl %esp,%ebp movl (%ebp),%ebx  ## causes problem reason,  movl $1,%eax      int $0x80         ## program should return exit status of %ebx value

as jester says, problem 64bit linux tools default making 64bit programs. has bad habit of writing answers in comments, i'll duplicate here:

as --32 test.s -o test.o; ld -melf_i386 test.o -o test

or

gcc -m32 foo.s -ffreestanding -nostdlib -o foo

you segfault at

movl (%ebp),%ebx

because %rsp isn't all-zero in upper 32 bits, %esp different address %rsp. find problem gdb. you'd have noticed had 64bit registers. see https://stackoverflow.com/tags/x86/info info on using gdb asm.

i'm going pick on line more:

pushl, %edx

besides being syntax error (extra comma), _start doesn't need save registers. x86-64 abi says should assume they're full of random garbage, except stack pointer. says %rdx has address of function should register atexit(), on current linux, %rdx zeroed on process entry. (command line args on stack.)

i presume things pretty same x86 32bit process startup.


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