So I'm currently trying to get the command line arguments using masm, here is what I've done so far:
.386
.MODEL FLAT
includelib kernel32.lib
includelib msvcrt.lib
__getmainargs PROTO C :DWORD
printf PROTO C :DWORD
.data
str_argv db "argv[1]: %s",0
.fardata?
argc dd ?
argv db 255 DUP(?)
env dd ?
.code
START:
push 0
push OFFSET env
push OFFSET argv
push OFFSET argc
call __getmainargs
add esp, 4*4 ;4 args
push [edi]
push OFFSET str_argv
call printf
add esp, 4 * 2 ;2 args
ret
END START
However this returns me a garbage string that does not correspond to the cmdline argument, in this case the module name.
Any ideas why this doesn't work? -> Also are there any other alternatives for accessing cmdline args?
Thanks in advance
You're pushing [edi] without having put the correct value into edi.
Change the declaration of argv to argv dd ?.
Then change the push [edi] to:
mov edi,argv
push dword ptr [edi+4]
And make sure you use the /SUBSYSTEM:CONSOLE option when linking.
Related
Greetings to all the geniuses of the digital age
Yesterday's task is still on the agenda: "Use the GetOpenFileName function to select a file. Check if the file is less than 3 days old, execute it. Otherwise, display a dialog asking to delete the file. If the user needs it, wipe." (Note: If a task is told to use a structure, it must be placed in dynamically allocated memory)"
I figured out how to open the file and now everything works like a Swiss watch. But another trouble arose.
How to determine the age of a file?
In general, I first thought to use GetFileTime to extract all data about the file time, then use FileTimeToLocalFileTime to convert it to local time, and using FileTimeToSystemTime - to system time. Then subtract one from the other using sub, and so on as per the task.
Here, the FileTimeToLocalFileTime function requires a FILETIME structure with the following parameters:
DWORD dwLowDateTime;
DWORD dwHighDateTime;
And the FileTimeToSystemTime function requires a SYSTEMTIME structure with the following parameters:
WORD wYear;
WORD wMonth;
WORD wDayOfWeek;
WORD wDay;
WORD wHour;
WORD wMinute;
WORD wSecond;
WORD wMilliseconds;
And how to be then? How to find the age of a file? Is there any alternative way? And if my method works, then what exactly and from what should I take it?
File.inc
include WINDOWS.inc
include user32.inc
include kernel32.inc
include comdlg32.inc
includelib user32.lib
includelib kernel32.lib
includelib comdlg32.lib
.data
Time_title db ' Lab_3',0
format db 'More than 3 days. Delete file?', 0
buf db 255 dup(0)
hFile dd 0
readed dd 0
hmem dd 0
File.asm
.386
.model flat,STDCALL
option casemap :none ;case sensitive
include Third.inc
include RADbg.inc
Mem_Alloc PROC Buf_Size:DWORD
add Buf_Size,4
invoke GlobalAlloc,GMEM_MOVEABLE or GMEM_ZEROINIT,Buf_Size
push eax
invoke GlobalLock,eax
pop [eax]
add eax,4
Mem_Alloc endp
Mem_Free PROC DATA:DWORD
mov eax,DATA
sub eax,4
mov eax,[eax]
push eax
push eax
call GlobalUnlock
call GlobalFree
Mem_Free endp
.code
Begin:
call main
invoke ExitProcess,NULL
main proc
LOCAL ftCreate, ftLocale: FILETIME;
LOCAL stUTC, stLocal: SYSTEMTIME;
invoke Mem_Alloc, 1000h
mov hmem, eax
invoke Mem_Alloc, sizeof OPENFILENAME
mov edi, eax
assume edi: ptr OPENFILENAME
xor eax, eax
mov [edi].lStructSize, sizeof OPENFILENAME
mov [edi].lpstrFile, offset buf
mov [edi].nMaxFile, 255
invoke GetOpenFileName, edi
invoke CreateFile, [edi].lpstrFile, GENERIC_READ,\
FILE_SHARE_READ, NULL, OPEN_EXISTING,\
FILE_ATTRIBUTE_NORMAL, NULL
mov hFile,eax ;
invoke GetFileTime, hFile, addr ftCreate, NULL, NULL
invoke FileTimeToLocalFileTime, addr ftCreate, addr ftLocale
invoke FileTimeToSystemTime, addr ftCreate, addr stUTC
cmp eax, 1
jz l1
invoke ReadFile, hFile, hmem, 1000h, addr readed, 0
invoke MessageBox, 0, hmem, addr Time_title, MB_OKCANCEL
jmp l2
l1:
invoke MessageBox, 0, addr format, addr Time_title, MB_OKCANCEL
cmp eax, IDOK
jne l2
invoke DeleteFile, addr [edi].lpstrFile
l2:
assume edi: dword
invoke CloseHandle, hFile
invoke Mem_Free, hmem
invoke Mem_Free, edi
ret
main endp
end Begin
As FILETIME and RtlTimeToSecondsSince1970 said, You should copy the low- and high-order parts of the file time to a ULARGE_INTEGER structure, perform 64-bit arithmetic on the QuadPart member.
So, subtract the 64-bit value in the ULARGE_INTEGER structure initialized with the file time from the 64-bit value of the ULARGE_INTEGER structure initialized with the current system time.
I have been trying to use stat in NASM to get file sizes. However, st_size returns 0. Can anyone explain why this happens?
Here is my code:
global _main
extern _printf
section .bss
stat resb 144
section .text
filename:
db "test.asm", 0 ; The name of this NASM file
format:
db "%lld", 10, 0
_main:
mov rax, 0x20000bc ; system call for stat
mov rdi, filename
mov rsi, stat
syscall ; returns 0
push rax
mov rdi, format
mov rsi, stat
mov rsi, [rsi + 96] ; the offset of st_size in __DARWIN_STRUCT_STAT64 as defined in <sys/stat.h> is 96
call _printf
pop rax
ret
This is not a duplicate of Get file size with stat syscall
You're using the wrong syscall. That's the one for backward compatibility with the 32-bit-sized structure. Of course, that means that the st_size field is not at the offset your code is expecting.
The stat() function's symbol name is not _stat, by default, since 10.6. Rather, it's _stat$INODE64. If you look at the assembly for that in /usr/lib/system/libsystem_kernel.dylib, you'll find that it uses the syscall value 0x2000152.
I want to write a MASM program similar to the following C++ program :
#include <Windows.h>
#include <iostream>
typedef UINT (_stdcall *FuncPtr)(LPCSTR lpCmdLine, UINT uCmdShow);
int main(void)
{
HMODULE hDll = LoadLibrary(TEXT("Kernel32.dll"));
FuncPtr func_addr = reinterpret_cast<FuncPtr>(GetProcAddress(hDll, "WinExec"));
(*func_addr)("C:\\WINDOWS\\system32\\calc.exe", SW_SHOWDEFAULT);
FreeLibrary(hDll);
return (0);
}
As you can see, this code execute the microsoft calculator. I just want to do the same thing using MASM but the execution fails.
Here's the MASM source code :
.386
.model flat, stdcall
option casemap:none
include \masm32\include\windows.inc
include \masm32\include\user32.inc
include \masm32\include\kernel32.inc
include \masm32\include\masm32.inc
include \masm32\include\msvcrt.inc
includelib \masm32\lib\user32.lib
includelib \masm32\lib\kernel32.lib
includelib \masm32\lib\masm32.lib
includelib \masm32\lib\msvcrt.lib
.data
LpFileName db "kernel32.dll", 0
procName db "WinExec", 0
display db "addr_func = 0x%x", 0
.data?
hModule HMODULE ?
procAddr FARPROC ?
.code
start:
invoke LoadLibrary, offset LpFileName
mov hModule, eax
invoke GetProcAddress, hModule, ADDR procName
mov procAddr, eax
INVOKE crt_printf, ADDR display, procAddr
mov esi, procAddr
call esi
db "C:\WINDOWS\system32\calc.exe"
invoke FreeLibrary, hModule
invoke ExitProcess, NULL
end start
The crt_printf output is correct. The same address is printed like withe the C++ program. So the address passed to call is the same one. However the execution fails.
Here's a MASM32 code which works but this time the address of the function WinExec is hardcoded like this :
.386
.model flat, stdcall
option casemap:none
include \masm32\include\windows.inc
.code
start:
jmp _Debut
_Final:
TCHAR 233
dword 42424242h
_Suite:
mov esi, 779e304eh
call esi
jmp _Final
_Debut:
xor eax, eax
push eax
call _Suite
db "C:\WINDOWS\system32\calc.exe"
end start
See the line mov esi, 779e304eh. But dynamically, there is a problem. If I disassemble the code just above we can see that the order of bytes is reversed.
8EEH047E379
Maybe it's not the case dynamically and maybe I need a keyword in the following line (between the comma and procAddr):
mov esi, procAddr
I cannot find the solution. I'm lost. Can anyone help me?
Thanks a lot in advance for your help.
The execution fails because you are not passing it's parameters.
Here you just call the function without any arguments or rather with invalid arguments (because whatever is currently on the stack will be taken and the stack is corrupted in the process).
mov esi, procAddr
call esi
You should do
push SW_SHOWDEFAULT
push offset YourPathToCalc
mov esi, procAddr
call esi
In your samplecode this is what is done here implicitly
xor eax, eax
push eax ; uCmdShow
call _Suite ; Returnadress is the address of the commandline so this is bascially the "push path"
Another thing you are missing is, that when WinExec returns, it will start executing the path in your case so you need a jmp somewhere after the call.
And as Gunner pointed out, the path must be 0 terminated.
To add to the correct answer Devolus posted, your path to calc is not NULL terminated.
This
"C:\WINDOWS\system32\calc.exe" is not correct!
Instead it should be:
"C:\WINDOWS\system32\calc.exe", 0
Also, if you are going to put strings in the code section to use, you need to give them a label in order to use them and you need to jump over them otherwise the CPU will try to execute the bytes.
INVOKE crt_printf, ADDR display, procAddr
mov esi, procAddr
push SW_SHOWDEFAULT
push offset Calc
call esi
jmp #F
Calc db "C:\WINDOWS\system32\calc.exe", 0
##:
invoke FreeLibrary, hModule
invoke ExitProcess, NULL
* EDIT *
To convert that code to Assembly using MASM, all that is needed is this:
.data
LpFileName db "kernel32", 0
procName db "WinExec", 0
Calc db "calc", 0
.code
start:
invoke LoadLibrary, offset LpFileName
push eax
invoke GetProcAddress, eax, ADDR procName
push SW_SHOWDEFAULT
push offset Calc
call eax
call FreeLibrary
invoke ExitProcess, NULL
end start
[SOLVED]
I'm trying to do my own assembly code to do what similar C code will do:
main()
{
scanf("%d",&integer_var); // here must be the address of the integer_var
printf("Your Value is:%d",integer_var);
}
Well this is in C, so I'm doing with NASM under linux with extern functions. scanf and printf and compile first with nasm and then with gcc.
Here's my code (is not right :D)
SECTION .text
argstr: db "%d",10,0
str: db "Your value is:%d",10,0
extern printf
extern scanf
SECTION .data
global main
main:
push ebp
mov esp,ebp
sub esp, 0x10 ;ok integer right?
mov [ebp-0x4],0x0 ;just put 0 number on our integer variable
mov eax,(ebp-0x4) ;here i don't know how to push the address of ebp-0x4
push ecx ;first push is last argument so here's our address to scanf
push argstr ;just the string format
call scanf ;call that to input something
;I have no idea how to do this
;but if i don't do this i get an error
;because the scanf won't clear the arguments on stack
;and what scanf can't return
pop edx ;maybe help here? but it works fine
pop edx
push [-0x4(ebp)] ;i want the value of our var :D
push str
call printf
pop edx ;clear the stack to avoid "segment fault" or something similar
pop edx
mov esp,ebp
pop ebp
ret ;the end :(
Compiler error:
a.asm:18: error: invalid operand type
a.asm:28: error: parser: expecting ]
Another thing: Do I need to align the stack on this case, by the way?
thanks guys ! :)
EDIT solved whole program!
well at least, I can print the variable with printf. scanf i will do later and then I will share here the last result:
SECTION .text
str: db "Value is:%d",10,0
extern printf
SECTION .data
global main
main:
push ebp ;the main function starts here.
mov ebp,esp
;
sub esp,4 ;we need 4bytes of space for the integer
and esp,0xfffffff0 ;align the stack
mov [esp-4], dword 0xff ;move the value 0xff to our var
mov eax,[esp-4] ;move our variable value to the eax
push eax ;second argument of printf
push str ;first argument of printf
call printf ;printf
;
add esp,16 ;this add to the stack pointer what we pushed basicly
mov ebp,esp ;if we don't do add 16 to esp it shows us
pop ebp ;a segment fault cuz ret doesnt pop saved ebp
ret ;of who whatever called this program :)
To load the address EBP-4 into EAX, use lea eax, [ebp-4]. (this is NOT the same as pushing the address.)
In order to push the value at memory location EBP-4, push dword [ebp-4] should work.
Then you need to specify operand size for one of your movs, too: mov [ebp-4], dword 0x0.
These will fix your current assembler errors, and make your program compile, but there are a few other errors in there that will probably prevent it from running.
Here's a working attempt that is close to yours:
;note the sections, the string literals are better in .rodata
;all code goes in .text
SECTION .rodata
;no newline after scanf string
argstr: db "%d",0
str: db "Your value is: %d",10,0
SECTION .text
extern printf
extern scanf
global main
main:
push ebp
mov ebp,esp ;move esp to ebp, NOT other way round!
sub esp, 4 ;4 bytes are enough for the local variable
;there are NO alignment requirements for this program
lea eax,[ebp-4]
push eax
push dword argstr
call scanf
add esp, 8 ;since we don't actually need the popped values
;we can increment esp instead of two pop edx
push dword [ebp-4]
push dword str
call printf
add esp, 8
mov esp,ebp
pop ebp
ret
I am trying just to print out the value of argc using the CommandLineToArgvW Window's API function in NASM. The following is what I have:
extern _ExitProcess#4
extern _GetCommandLineA#0
extern _CommandLineToArgvW#8
extern printf
global _start
section .code
Format:
db "%d",10,0
FormatS:
db "%s",10,0
_start:
push ebp
mov ebp, esp
sub esp, 4 ; Create empty space for ArgC
call _GetCommandLineA#0
push eax; Push value beneath ArgC
mov ebx, ebp ; Set ebx to ebp
sub ebx, 4
push dword ebx ; pushes ArgC address onto stack
push dword [ebp - 8] ; pushes pointer to Command Line String
call _CommandLineToArgvW#8
push dword [ebp - 4]
push Format
call printf
push dword 0
call _ExitProcess#4
No matter what I do, the value for argc is 1. What am I doing wrong?
I assemble and link with these commands:
nasm -fwin32 FunctionTests.asm
golink FunctionTests.obj kernel32.dll msvcrt.dll shell32.dll /console /entry _start
FunctionTests.exe hi asdf asdf asdf asdf
As you can see, from the last line, argc should be 6.
Change _GetCommandLineA to _GetCommandLine*W* CommandLineToArgv expects a pointer to a UNICODE string.
MASM but just about the same:
start:
push ebp
mov ebp, esp
sub esp, 4
call GetCommandLineW
lea ecx, dword ptr[ebp - 4] ; need the address of local
push ecx ; address of local
push eax ; pointer to unicode string
call CommandLineToArgvW
push dword ptr [ebp - 4] ; value of local
push offset Format
call crt_printf
add esp, 8
; this is all? Then we don't have to restore stack.
push 0
call ExitProcess
end start
and this is the output:
D:\Projects>ConTest.exe boo boo I see you
6
D:\Projects>
Set a breakpoint just before you call CommandLineToArgvW and inspect the parameters you're about to pass. Observe that the first parameter you are passing is not a pointer to a string. It is a pointer to a pointer to a string.
You need to use GetCommandLineW rather than GetCommandLineA.
You are using CommandLineToArgvW with an ANSI string, use GetCommandLineW to get the command line in unicode.
You are also not dereferencing the pointer to the command line:
push ebx ; pushes ArgC address onto stack