Programming Forums > Application Development > Assembly

rsnd · Aug 12th, 2006, 10:37 PM

What is this?

lea     ecx, ds:80h[ecx*4]

is it simply ecx = ecx * 4? Does it have anything to do with the data segment?

it appears here:

(Toggle Plain Text)

this::0 = &some_vector_table;
this::8 = 0;

if (unknown_global_1000EA80 == 0 || unknown_global_1000EA84 & 31==0) {
	mov     ecx, unknown_global_1000EA84
	lea     ecx, ds:80h[ecx*4]
	unknown_global_1000EA80 = realloc(unknown_global_1000EA80, ecx);
}

unknown_global_1000EA80[unknown_global_1000EA84] = &this;
unknown_global_1000EA84++;
this::12 = 0;
if (someglobalsocketvariable == 0) {
	some_fdset.fd_count = 0;
	other_fd.fd_count = 0;
}

thanks

Harakim · Aug 13th, 2006, 4:35 AM

I haven't programmed in x86 assembly for years.

lea is load effective address

lea ecx, ds:80h[ecx*4]

This loads an address into ecx. It doesn't actually load anything from memory. It just calculates the address. I think it basically allows you to use mathmatical operations rather than instructions to make code cleaner.

ds is one of the segmentation registers. It seems like I used ds to access the hard drive. Since you have the word socket in there, it makes me think it could be the network, although I'm speculating now.

Hopefully I helped a little.

DaWei · Aug 13th, 2006, 1:07 PM

Using lea is like setting a pointer to point to a variable, rather than fetching the variable. DS is the data segment register. It is not required that one use if strictly for that, more in the nature of a convention.

rsnd · Aug 14th, 2006, 3:09 AM

hmm... I dont understand that data segment register bit: "ds:80h." There are a couple of strings declared on 80h offset of data segment and should not be relevent. What is its purpose there? From what I see its calculating the new size of a buffer. From what I remember, my college professor used to use "rAB:rCD:rEF" notation to denote higher resolution numbers.

Aug 12th, 2006, 10:37 PM	#1
rsnd Hobbyist Programmer Join Date: Jun 2005 Location: Helltown Posts: 162 Rep Power: 4	someone help out this newbie What is this? (Toggle Plain Text) lea ecx, ds:80h[ecx4] lea ecx, ds:80h[ecx4] is it simply ecx = ecx * 4? Does it have anything to do with the data segment? it appears here: (Toggle Plain Text) this::0 = &some_vector_table; this::8 = 0; if (unknown_global_1000EA80 == 0 \|\| unknown_global_1000EA84 & 31==0) { *mov ecx, unknown_global_1000EA84 lea ecx, ds:80h[ecx4]** unknown_global_1000EA80 = realloc(unknown_global_1000EA80, ecx); } unknown_global_1000EA80[unknown_global_1000EA84] = &this; unknown_global_1000EA84++; this::12 = 0; if (someglobalsocketvariable == 0) { some_fdset.fd_count = 0; other_fd.fd_count = 0; } this::0 = &some_vector_table; this::8 = 0; if (unknown_global_1000EA80 == 0 \|\| unknown_global_1000EA84 & 31==0) { mov ecx, unknown_global_1000EA84 lea ecx, ds:80h[ecx*4] unknown_global_1000EA80 = realloc(unknown_global_1000EA80, ecx); } unknown_global_1000EA80[unknown_global_1000EA84] = &this; unknown_global_1000EA84++; this::12 = 0; if (someglobalsocketvariable == 0) { some_fdset.fd_count = 0; other_fd.fd_count = 0; } thanks __________________ Spread your wings and fly! Chicken!

Aug 13th, 2006, 1:07 PM	#3
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	Using lea is like setting a pointer to point to a variable, rather than fetching the variable. DS is the data segment register. It is not required that one use if strictly for that, more in the nature of a convention. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Aug 14th, 2006, 3:09 AM	#4
rsnd Hobbyist Programmer Join Date: Jun 2005 Location: Helltown Posts: 162 Rep Power: 4	hmm... I dont understand that data segment register bit: "ds:80h." There are a couple of strings declared on 80h offset of data segment and should not be relevent. What is its purpose there? From what I see its calculating the new size of a buffer. From what I remember, my college professor used to use "rAB:rCD:rEF" notation to denote higher resolution numbers. __________________ Spread your wings and fly! Chicken!

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Aug 13th, 2006, 4:35 AM	#2
Harakim Hobbyist Programmer Join Date: May 2006 Location: West Jordan, Utah, United States Posts: 176 Rep Power: 3	I haven't programmed in x86 assembly for years. lea is load effective address lea ecx, ds:80h[ecx*4] This loads an address into ecx. It doesn't actually load anything from memory. It just calculates the address. I think it basically allows you to use mathmatical operations rather than instructions to make code cleaner. ds is one of the segmentation registers. It seems like I used ds to access the hard drive. Since you have the word socket in there, it makes me think it could be the network, although I'm speculating now. Hopefully I helped a little.

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Programming Forums > Application Development > Assembly

someone help out this newbie