assembly - Linux AT&T command-line parameters -
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i'm trying learn assembly programming on linux, googled/created simple implementation of "cat", little program not work command-line arguments (it says "colud't open file"). when uncomment "fname" line, works, file i/o fine. think stack-part broken :/ here's code:
.code32 .section .data msg_err_open: .asciz "colud't open file.\n" msg_err_open_len: .long . - msg_err_open fname: .asciz "test.txt" .section .bss .equ bufsize, 1024 .lcomm buf, bufsize .section .text .globl _start .align 4 _start: # popl %ebx # argc # popl %ebx # argv[0] # popl %ebx # argv[1] (file) # open movl $5, %eax # open( # movl 8(%esp), %ebx # filename, ???????????????? movl $fname, %ebx movl $0, %ecx # readonly int $0x80 # ) test %eax, %eax # megnyitás sikerült? js err_open # ha negatív # read movl %eax, %ebx # file descriptor eax->ebx movl $3, %eax # read( fd (ebx), movl $buf, %ecx # buffer, movl $bufsize, %edx # size int $0x80 # ) # close movl $6, %eax # close( fd (ebx) int $0x80 # ) # write movl $4, %eax # write( movl $1, %ebx # stdout, movl $buf, %ecx # buffer int $0x80 #) # exit movl $1, %eax # exit( movl $0, %ebx # 0 int $0x80 # ) err_open: # write (msg_err_open) movl $4, %eax movl $1, %ebx movl $msg_err_open, %ecx movl $msg_err_open_len, %edx # length int $0x80 # exit(1) movl $1, %eax movl $1, %ebx int $0x80 i comple/link way:
pfile.s -o pfile.o ld pfile.o -o pfile my linux distro is:
debian 3.2.41-2+deb7u2 as version:
2.22 (x86_64-linux-gnu) i think solution trivial, don't see it. want run on 32 bit mode, x64 pretty hard me now. thank time!
oh, see problem. nice have included how build program (+1 that). if check resulting executable using file command, bet says 64 bit:
$ file pfile pfile: elf 64-bit lsb executable, x86-64, version 1 (sysv), statically linked, not stripped to make 32 bit program should use:
$ --32 pfile.s -o pfile.o $ ld -melf_i386 pfile.o -o pfile $ file pfile pfile: elf 32-bit lsb executable, intel 80386, version 1 (sysv), statically linked, not stripped $ ./pfile pfile.s .code32 .section .data ... alternatively can gcc -m32 -nostdlib pfile.s -o pfile
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