importing stdin

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m

Joined: 28 Dec 2006
Posts: 304
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m 03 Jun 2007, 00:27

Code:

cinvoke fgets,buff,128,[stdin]

i cant get it work,Why?

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03 Jun 2007, 00:27

kohlrak

Joined: 21 Jul 2006
Posts: 1421
Location: Uncle Sam's Pad

kohlrak 03 Jun 2007, 00:39

MSDN wrote:

char *fgets(
char* string,
int n,
FILE *stream
);

The third parameter is a pointe,r in your code, it's the value referanced by the pointer. Give it a pointer, unless the pointer is stored in the variable stdin, which in that case, you'll have to show the rest of the program to see what is wrong.

03 Jun 2007, 00:39

m

Joined: 28 Dec 2006
Posts: 304
Location: in

m 03 Jun 2007, 00:57

The code is written for PE console format. fgets is supposed to be imported with the help of import32.inc macros and the stdin is the famous stdin that we can use in C.

I wanted to do what looks like this in C:

Code:

fgets(buff,128,stdin);

Help !

03 Jun 2007, 00:57

kohlrak

Joined: 21 Jul 2006
Posts: 1421
Location: Uncle Sam's Pad

kohlrak 03 Jun 2007, 01:01

Try this...

Code:

invoke  GetStdHandle, STD_INPUT_HANDLE
cinvoke fgets, buff, 128, eax

GetStdHandle is in kernel32.dll i think... Not sure, but it *MIGHT* have A and W versions, so if you get an error that it's not found, just put an A there.

03 Jun 2007, 01:01

m

Joined: 28 Dec 2006
Posts: 304
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m 03 Jun 2007, 01:10

Thanks a lot Mr Kohlrak !
Any thoughts on why we can't access the stdin directly ?
I am worried cause if I use GetStdHandle it will make my code unportable on Linux.

03 Jun 2007, 01:10

kohlrak

Joined: 21 Jul 2006
Posts: 1421
Location: Uncle Sam's Pad

kohlrak 03 Jun 2007, 01:12

It's because STDIN is program specific. If you want STDIN, you have to get it dynamically (from what i've seen)... In windows that is. I don't know how to do so in linux.

03 Jun 2007, 01:12

m

Joined: 28 Dec 2006
Posts: 304
Location: in

m 03 Jun 2007, 01:21

Thanks a lot again Mr. Kohlrak !
Looks like, when you think Assembly, then you forget Portability !

03 Jun 2007, 01:21

kohlrak

Joined: 21 Jul 2006
Posts: 1421
Location: Uncle Sam's Pad

kohlrak 03 Jun 2007, 01:26

True, but anything that uses something outside the standard library, and it looses compatability, and many forget this. I'm looking at your window code, now.

03 Jun 2007, 01:26

Goplat

Joined: 15 Sep 2006
Posts: 181

Goplat 03 Jun 2007, 02:34

kohlrak wrote:

Try this...
Code:
invoke  GetStdHandle, STD_INPUT_HANDLE
cinvoke fgets, buff, 128, eax    
GetStdHandle is in kernel32.dll i think... Not sure, but it *MIGHT* have A and W versions, so if you get an error that it's not found, just put an A there.

That won't work; GetStdHandle returns a win32 HANDLE, but fgets expects a pointer to a FILE structure.

Usually C's stdin/stdout/stderr are not actual variables, but macros. If you look in stdio.h you will find something like #define stdin &_iob[0], #define stdout &_iob[1], and #define stderr &_iob[2], where _iob is an array of FILEs.

03 Jun 2007, 02:34

kohlrak

Joined: 21 Jul 2006
Posts: 1421
Location: Uncle Sam's Pad

kohlrak 03 Jun 2007, 02:42

Then how do you propose he gets the pointer?

03 Jun 2007, 02:42

m

Joined: 28 Dec 2006
Posts: 304
Location: in

m 03 Jun 2007, 02:56

Yeah Goplat, please tell me how do I get the pointer !

03 Jun 2007, 02:56

Goplat

Joined: 15 Sep 2006
Posts: 181

Goplat 03 Jun 2007, 05:07

I assume you're using msvcrt? Just import _iob, then [_iob] is the address of stdin. To get stdout or stderr you add 32 or 64, since there are 32 bytes in a FILE structure.

There are also functions called __p__iob and __iob_func, which seem to always just return the same address you get from importing _iob. If you're using a different version of the C library which doesn't have plain _iob then try those.

03 Jun 2007, 05:07

m

Joined: 28 Dec 2006
Posts: 304
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m 03 Jun 2007, 11:23

Hi Mr. Goplat, I believe that in PE console format fasm (or the macros) does not allow me to import a variable !
I'll try other option suggested by you. And yes I was using msvcrt.dll.

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03 Jun 2007, 11:23

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
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LocoDelAssembly 03 Jun 2007, 14:43

Do you really need stdin because your code should read both files and stdin or you just need to read from stdin? If the latter is the case use gets instead http://board.flatassembler.net/topic.php?t=3895

If you need pointer to _iob[0] then according to what I see in IDApro you have "__iob_func" and "__p__iob" which returns it. Also you have "_iob" which is a variable. To import a variable just add it in the import table like if it were a function but never call it, just access it with "[_iob]".

03 Jun 2007, 14:43

vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid 03 Jun 2007, 15:30

yeah, doing it "the right way" in assembly isn't very nice:

MSVC headers say:

Code:

#define stdin  (&__iob_func()[0])

03 Jun 2007, 15:30

kohlrak

Joined: 21 Jul 2006
Posts: 1421
Location: Uncle Sam's Pad

kohlrak 03 Jun 2007, 16:57

Just out of shear curiosity, would it be the same in crtdll as msvcrt? And is there another stdin, because i feel 32 bytes is a bit small for client data...

APJ 9 wrote:

CGI Environment
---------------
A CGI program is not required to read data, but it is required to send it.
Client data is availiable on the StdIn. The length is in the CONTENT_LENGTH
environment variable. Also, 255 bytes of the data is in the QUERY_STRING
EnvVar. All out put must start with "Content-Type:" a space, the type, and two
newlines (CrLf). Common types include: "text/plain", "text/html", or
"image/gif". Example output:

03 Jun 2007, 16:57

Goplat

Joined: 15 Sep 2006
Posts: 181

Goplat 03 Jun 2007, 17:23

m wrote:

Hi Mr. Goplat, I believe that in PE console format fasm (or the macros) does not allow me to import a variable !

It worked when I tried it...

LocoDelAssembly wrote:

Do you really need stdin because your code should read both files and stdin or you just need to read from stdin? If the latter is the case use gets instead http://board.flatassembler.net/topic.php?t=3895

Only if you don't mind crashing when the user types a line that's too long.

kohlrak wrote:

Just out of shear curiosity, would it be the same in crtdll as msvcrt?

Yep, although crtdll only exports _iob itself; it doesn't have either of the functions.

Quote:

And is there another stdin, because i feel 32 bytes is a bit small for client data...

The FILE struct doesn't contain the buffer directly, just pointers to it. Here's the complete definition, if you're curious.

Code:

struct _iobuf {
        char *_ptr;
        int   _cnt;
        char *_base;
        int   _flag;
        int   _file;
        int   _charbuf;
        int   _bufsiz;
        char *_tmpfname;
        };
typedef struct _iobuf FILE;

03 Jun 2007, 17:23

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 03 Jun 2007, 17:31

Goplat wrote:

Only if you don't mind crashing when the user types a line that's too long.

Yeah sorry, I forgot it doesn't have the "n" parameter.

03 Jun 2007, 17:31

kohlrak

Joined: 21 Jul 2006
Posts: 1421
Location: Uncle Sam's Pad

kohlrak 03 Jun 2007, 17:50

Explains a bit. Now to figure out how to imporat all the other data for CGI apps, but that's for another topic, since that would be off topic. So i'm assuming _ptr would be to the first thing in the string, or would that be _base? ...hm, that is an interesting structure...

03 Jun 2007, 17:50

vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid 03 Jun 2007, 17:55

this is the problem with using libc in assembly. You need to code at least some small wrapper for libc to use it

03 Jun 2007, 17:55

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