[Assembler] scanf How-To

Na akumulator?! EAX register tukaj ne igra nobene vloge.

Pri scanf bi pričakoval vsaj še kakšen "%s" format string. V stilu "push naslov" (oz. najbrz lahko kar "push sporocilo"), "push formatstr", "call _scanf", "add esp, 8". Oz glede na to, da hočeš tisto kar je bilo prebrano takoj spet izpisati najbrž lahko narediš kar brez tega in direktno pokličeš printf s "%s" in naslov.

Če daš "add esp, 4" in pokličeš le printf s sporočilom od uporabnika si ranljiv na format string napade. Druga stvar je pa preveč vpisanih znakov pri scanf (buffer overflow), ampak to lahko rešiš npr. z uporabo "%10s".

whatever je 7. nov 2010 ob 18:54 izjavil:

One great advantage of interfacing C and assembly is that allows as-
sembly code to access the large C library and user-written functions. For
example, what if one wanted to call the scanf function to read in an integer
from the keyboard? Figure 4.14 shows code to do this. One very important
point to remember is that scanf follows the C calling standard to the letter.
This means that it preserves the values of the EBX, ESI and EDI registers;
however, the EAX, ECX and EDX registers may be modified! In fact, EAX
will definitely be changed, as it will contain the return value of the scanf
call. For other examples of using interfacing with C, look at the code in
asm io.asm which was used to create asm io.obj.

Torej v EAX shrani.

Ok to že - EAX je ponavadi za return value, odvisno od načina klica. Se popravljam, ni tako da EAX ne bi igral nobene vloge. Samo kaj shrani tja scanf()...

Return Value
On success, the function returns the number of items succesfully read. This count can match the expected number of readings or fewer, even zero, if a matching failure happens.
In the case of an input failure before any data could be successfully read, EOF is returned.

To pa najbrž ni tisto, kar te zanima.