CODEWITHSUNDEEP
cassemblyx86
gnometorule
gnometorule

Reputation: 2139

X86 32b assembly - using atoll

Under Ubuntu 12.04., and using x86 32 bit assembly possibly with C libraries, I need to use a number n which is 

 2^31 - 1 < n <= 2^63 -1

On my system, C ints are 32 bit; and long longs 64 bit. I know how to proceed after having the number, but am stuck on getting the number ready.

My planned approach was as follows: 

 - store n as a string in the .data segment    

- use atoll (pushl $n_Str, call atoll)   

 - retrieve the converted value, and store it in two consecutive int-sized storage locations (taking note of likely little-endian storage)

As the usual 32 bit return value convention through %eax cannot apply (or only possibly through a pointer, which I have checked seems to not be the case (%eax points to inaccessible memory after)), I assumed the value might be in (%eax, %ebx). I checked all permutations of high/low assuming this were the case, but it doesn't seem to be (if it is, and I messed up, kindly point out the proper way). The man (and man 3) page for atoll doesn't help.

How do I retrieve the converted integer? If this approach is impossible (strtoll has the same issue), any suggestions for alternatives?

Upvotes: 1

Views: 1440

Answers (1)

Sedat Kapanoglu
Sedat Kapanoglu

Reputation: 47640

It seems to depend on calling convention and compiler. __stdcall functions return 64-bit integers in pairs in EAX:EDX registers. __cdecl functions return a pointer to stack to the integer on GCC. __cdecl functions on Visual C++ return a pair in EAX:EDX.

Here is the source: http://en.wikibooks.org/wiki/X86_Assembly/High-Level_Languages

Upvotes: 2

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