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  • How is a relative JMP (x86) implemented in an Assembler?

    - by Pindatjuh
    While building my assembler for the x86 platform I encountered some problems with encoding the JMP instruction: enc inst size in bytes EB cb JMP rel8 2 E9 cw JMP rel16 4 (because of 0x66 16-bit prefix) E9 cd JMP rel32 5 ... (from my favourite x86 instruction website, http://siyobik.info/index.php?module=x86&id=147) All are relative jumps, where the size of each encoding (operation + operand) is in the third column. Now my original (and thus fault because of this) design reserved the maximum (5 bytes) space for each instruction. The operand is not yet known, because it's a jump to a yet unknown location. So I've implemented a "rewrite" mechanism, that rewrites the operands in the correct location in memory, if the location of the jump is known, and fills the rest with NOPs. This is a somewhat serious concern in tight-loops. Now my problem is with the following situation: b: XXX c: JMP a e: XXX ... XXX d: JMP b a: XXX (where XXX is any instruction, depending on the to-be assembled program) The problem is that I want the smallest possible encoding for a JMP instruction (and no NOP filling). I have to know the size of the instruction at c before I can calculate the relative distance between a and b for the operand at d. The same applies for the JMP at c: it needs to know the size of d before it can calculate the relative distance between e and a. How do existing assemblers implement this, or how would you implement this? This is what I am thinking which solves the problem: First encode all the instructions to opcodes between the JMP and it's target, and if this region contains a variable-sized opcode, use the maximum size, i.e. 5 for JMP. Then in some conditions, the JMP is oversized (because it may fit in a smaller encoding): so another pass will search for oversized JMPs, shrink them, and move all instructions ahead), and set absolute branching instructions (i.e. external CALLs) after this pass is completed. I wonder, perhaps this is an over-engineered solution, that's why I ask this question.

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  • How to find the jmp address during a x86 function call?

    - by Bruce
    Suppose we have a call foo statement. So when the assembler encounters a call statement it breaks it down into - push ip + 6 jmp <addr of foo> I have the return address in a register ebx. Now I want to find out the "addr of foo". How do I do it? I want to confirm that the push statement is present before the jmp. Will the memory map look something like this? ------- push (what will be the value stored in this byte?? opcode ??) ------- jmp (what will be the value stored in this byte?? opcode ??) ------- jmp byte 1 ------- jmp byte 2 ------- jmp byte 3 ------- jmp byte 4 ------- return address stored in ebx ------- What are the opcodes for push and jmp?

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  • JMP instruction in Flex/bison

    - by Imran
    Hallo everybody, Can someone help me out of my situation, im searching for a instrucior that implements the JMP (Jump) instructior like in Assembler. I've found out that it could be withe the goto function of Flex/Bison but i have no really idea how to do. Have got anyone idea. Im very grateful of yours help. Thanks. Here is an example how it looks like. with the JMP instructor, he goes to the label L1. :L1 IF FLAG AND X"0001" EVT 23; ELSE WAIT 500 ms; JMP L1; END IF;

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  • Why is the CLR's jmp instruction unverifiable?

    - by naasking
    The title says it all. I've known about the jmp instruction for awhile, but it never struck me as being even remotely unsafe. I recently had cause to check the CIL specs and was very surprised to discover jmp is considered unverifiable. Any explanations would be much appreciated.

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  • ASM x86 relative JMP

    - by benlaug
    Hi, I'm doing some ASM code in a C code with the asm function. My environment is DVL with gcc version 3. Hi need to make a JMP to a relative address like %eip+0x1f. How can I do this ? Thanks

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  • Switch case assembly level code

    - by puffadder
    Hi All, I am programming C on cygwin windows. After having done a bit of C programming and getting comfortable with the language, I wanted to look under the hood and see what the compiler is doing for the code that I write. So I wrote down a code block containing switch case statements and converted them into assembly using: gcc -S foo.c Here is the C source: switch(i) { case 1: { printf("Case 1\n"); break; } case 2: { printf("Case 2\n"); break; } case 3: { printf("Case 3\n"); break; } case 4: { printf("Case 4\n"); break; } case 5: { printf("Case 5\n"); break; } case 6: { printf("Case 6\n"); break; } case 7: { printf("Case 7\n"); break; } case 8: { printf("Case 8\n"); break; } case 9: { printf("Case 9\n"); break; } case 10: { printf("Case 10\n"); break; } default: { printf("Nothing\n"); break; } } Now the resultant assembly for the same is: movl $5, -4(%ebp) cmpl $10, -4(%ebp) ja L13 movl -4(%ebp), %eax sall $2, %eax movl L14(%eax), %eax jmp *%eax .section .rdata,"dr" .align 4 L14: .long L13 .long L3 .long L4 .long L5 .long L6 .long L7 .long L8 .long L9 .long L10 .long L11 .long L12 .text L3: movl $LC0, (%esp) call _printf jmp L2 L4: movl $LC1, (%esp) call _printf jmp L2 L5: movl $LC2, (%esp) call _printf jmp L2 L6: movl $LC3, (%esp) call _printf jmp L2 L7: movl $LC4, (%esp) call _printf jmp L2 L8: movl $LC5, (%esp) call _printf jmp L2 L9: movl $LC6, (%esp) call _printf jmp L2 L10: movl $LC7, (%esp) call _printf jmp L2 L11: movl $LC8, (%esp) call _printf jmp L2 L12: movl $LC9, (%esp) call _printf jmp L2 L13: movl $LC10, (%esp) call _printf L2: Now, in the assembly, the code is first checking the last case (i.e. case 10) first. This is very strange. And then it is copying 'i' into 'eax' and doing things that are beyond me. I have heard that the compiler implements some jump table for switch..case. Is it what this code is doing? Or what is it doing and why? Because in case of less number of cases, the code is pretty similar to that generated for if...else ladder, but when number of cases increases, this unusual-looking implementation is seen. Thanks in advance.

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  • Using memcpy to change a jnz to a jmp.

    - by Phil
    Not used memcpy much but here's my code that doesn't work. memcpy((PVOID)(enginebase+0x74C9D),(void *)0xEB,2); (enginebase+0x74C9D) is a pointer location to the address of the bytes that I want to patch. (void *)0xEB is the op code for the kind of jmp that I want. Only problem is that this crashes the instant that the line tries to run, I don't know what I'm doing wrong, any incite?

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  • GCC/X86, Problems with relative jumps

    - by Ian Kelly
    I'm trying to do a relative jump in x86 assembly, however I can not get it to work. It seems that for some reason my jump keeps getting rewritten as an absolute jump or something. A simple example program for what I'm trying to do is this: .global main main: jmp 0x4 ret Since the jmp instruction is 4 bytes long and a relative jump is offset from the address of the jump + 1, this should be a fancy no-op. However, compiling and running this code will cause a segmentation fault. The real puzzler for me is that compiling it to the object level and then disassembling the object file shows that it looks like the assembler is correctly doing a relative jump, but after the file gets compiled the linker is changing it into another type of jump. For example if the above code was in a file called asmtest.s: $gcc -c asmtest.s $objdump -D asmtest.o ... Some info from objdump 00000000 <main>: 0: e9 00 00 00 00 jmp 5 <main+0x5> 5: c3 ret This looks like the assembler correctly made a relative jump, although it's suspicious that the jmp instruction is filled with 0s. I then used gcc to link it then disassembled it and got this: $gcc -o asmtest asmtest.o $objdump -d asmtest ...Extra info and other disassembled functions 08048394 <main>: 8048394: e9 6b 7c fb f7 jmp 4 <_init-0x8048274> 8048399: c3 ret This to me looks like the linker rewrote the jmp statement, or substituted the 5 in for another address. So my question comes down to, what am I doing wrong? Am I specifying the offset incorrectly? Am I misunderstanding how relative jumps work? Is gcc trying to make sure I don't do dangerous things in my code?

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  • How to keep unreachable code?

    - by Gabriel
    I'd like to write a function that would have some optional code to execute or not depending on user settings. The function is cpu-intensive and having ifs in it would be slow since the branch predictor is not that good. My idea is making a copy in memory of the function and replace NOPs with jumps when I don't want to execute some code. My working example goes like this: int Test() { int x = 2; for (int i=0 ; i<10 ; i++) { x *= 2; __asm {NOP}; // to skip it replace this __asm {NOP}; // by JMP 2 (after the goto) x *= 2; // Op to skip or not x *= 2; } return x; } In my test's main, I copy this function into a newly allocated executable memory and replace the NOPs by a JMP 2 so that the following x *= 2 is not executed. The problem is that I would have to change the JMP operand every time I change the code to be skipped. An alternative that would fix this problem would be: __asm {NOP}; // to skip it replace this __asm {NOP}; // by JMP 2 (after the goto) goto dont_do_it; x *= 2; // Op to skip or not dont_do_it: x *= 2; This way, as a goto uses 2 bytes of binary, I would be able to replace the NOPs by a fixed JMP of alway 2 in order to skip the goto. Unfortunately, in full optimization mode, the goto and the x*=2 are removed because they are unreachable at compilation time. Hence the need to keep that dead code.

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  • Assembly Language bug with space character

    - by Bobby
    Having a bit of difficulty getting my input to print once a white space character is inputted. So far, i have it to display the uppercase/lowercase of the input but once i enter a string it doesnt read whats after the white space character. any suggestions? EDIT: intel x86 processor and im using EMU8086 org 100h include 'emu8086.inc' printn "Enter string to convert" mov dx,20 call get_string printn mov bx,di mov ah,0eh mov al,[ds+bx] cmp al, 41h cmp al, 5Ah jle ToLower1 cmp al, 61h cmp al, 7ah jle ToUpper1 ToLower1: add al, 20h int 10h jmp stop1 ToUpper1: sub al, 20h int 10h stop1: inc bx mov al,[ds+bx] cmp al, 41h cmp al, 5Ah jle ToLower2 cmp al, 61h cmp al, 7ah jle ToUpper2 ToLower2: add al, 20h int 10h jmp stop2 ToUpper2: sub al, 20h int 10h stop2: inc bx mov al,[ds+bx] cmp al, 41h cmp al, 5Ah jle ToLower3 cmp al, 61h cmp al, 7ah jle ToUpper3 ToLower3: add al, 20h int 10h jmp stop3 ToUpper3: sub al, 20h int 10h stop3: inc bx mov al,[ds+bx] cmp al, 41h cmp al, 5Ah jle ToLower4 cmp al, 61h cmp al, 7ah jle ToUpper4 ToLower4: add al, 20h int 10h jmp stop4 ToUpper4: sub al, 20h int 10h stop4: inc bx mov al,[ds+bx] cmp al, 41h cmp al, 5Ah jle ToLower5 cmp al, 61h cmp al, 7ah jle ToUpper5 ToLower5: add al, 20h int 10h jmp stop5 ToUpper5: sub al, 20h int 10h stop5: printn hlt define_get_string define_print_string end

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  • Runtime error of TASM language help!

    - by dominoos
    .model small .stack 400h .data message db "hello. ", 0ah, 0dh, "$" firstdigit db ? seconddigit db ? thirddigit db ? number dw ? newnumber db ? anumber dw 0d bnumber dw 0d Firstn db 0ah, 0dh, "Enter first 3 digit number: ","$" secondn db 0ah, 0dh, "Enter second 3 digit number: ","$" messageB db 0ah, 0dh, "HCF of two number is: ","$" linebreaker db 0ah, 0dh, ' ', 0ah, 0dh, '$' .code Start: mov ax, @data ; establish access to the data segment mov ds, ax ; mov number, 0d mov dx, offset message ; print the string "yob choi 0648293" mov ah, 9h int 21h num: mov dx, offset Firstn ; print the string "put 1st 3 digit" mov ah, 9h int 21h ;run JMP FirstFirst ; jump to FirstFirst FirstFirst: ;first digit mov ah, 1d ;bios code for read a keystroke int 21h ;call bios, it is understood that the ascii code will be returned in al mov firstdigit, al ;may as well save a copy sub al, 30h ;Convert code to an actual integer cbw ;CONVERT BYTE TO WORD. This takes whatever number is in al and ;extends it to ax, doubling its size from 8 bits to 16 bits ;The first digit now occupies all of ax as an integer mov cx, 100d ;This is so we can calculate 100*1st digit +10*2nd digit + 3rd digit mul cx ;start to accumulate the 3 digit number in the variable imul cx ;it is understood that the other operand is ax ; the result will use both dx::ax ;dx will contain only leading zeros add anumber, ax ;save ;Second Digit mov ah, 1d ;bios code for read a keystroke int 21h ;call bios, it is understood that the ascii code will be returned in al mov seconddigit, al ;may as well save a copy sub al, 30h ;Convert code to an actual integer cbw ;CONVERT BYTE TO WORD. This takes whatever number is in al and ;extends it to ax, boubling its size from 8 bits to 16 bits ;The first digit now occupies all of ax as an integer mov cx, 10d ;continue to accumulate the 3 digit number in the variable mul cx ;it is understood that the other operand is ax, containing first digit ;the result will use both dx::ax ;dx will contain only leading zeros. add anumber, ax ;save ;third Digit mov ah, 1d ;samething as above int 21h ; mov thirddigit, al ; sub al, 30h ; cbw ; add anumber, ax ; jmp num2 ;go to checks Num2: mov dx, offset secondn ; print the string "put 2nd 3 digits" mov ah, 9h int 21h ;run JMP SecondSecond SecondSecond: ;first digit mov ah, 1d ;bios code for read a keystroke int 21h ;call bios, it is understood that the ascii code will be returned in al mov firstdigit, al ;may as well save a copy sub al, 30h ;Convert code to an actual integer cbw ;CONVERT BYTE TO WORD. This takes whatever number is in al and ;extends it to ax, doubling its size from 8 bits to 16 bits ;The first digit now occupies all of ax as an integer mov cx, 100d ;This is so we can calculate 100*1st digit +10*2nd digit + 3rd digit mul cx ;start to accumulate the 3 digit number in the variable imul cx ;it is understood that the other operand is ax ; the result will use both dx::ax ;dx will contain only leading zeros add bnumber, ax ;save ;Second Digit mov ah, 1d ;bios code for read a keystroke int 21h ;call bios, it is understood that the ascii code will be returned in al mov seconddigit, al ;may as well save a copy sub al, 30h ;Convert code to an actual integer cbw ;CONVERT BYTE TO WORD. This takes whatever number is in al and ;extends it to ax, boubling its size from 8 bits to 16 bits ;The first digit now occupies all of ax as an integer mov cx, 10d ;continue to accumulate the 3 digit number in the variable mul cx ;it is understood that the other operand is ax, containing first digit ;the result will use both dx::ax ;dx will contain only leading zeros. add bnumber, ax ;save ;third Digit mov ah, 1d ;samething as above int 21h ; mov thirddigit, al ; sub al, 30h ; cbw ; add bnumber, ax ; jmp compare ;go to compare compare: CMP ax, anumber ;comparing numbB and Number JA comp1 ;go to comp1 if anumber is bigger CMP ax, anumber ; JB comp2 ;go to comp2 if anumber is smaller CMP ax, anumber ; JE equal ;go to equal if two numbers are the same JMP compare ;go to compare (avioding error) comp1: SUB ax, anumber; subtract smaller number from bigger number JMP compare ; comp2: SUB anumber, ax; subtract smaller number from bigger number JMP compare ; equal: mov ah, 9d ;make linkbreak after the 2nd 3 digit number mov dx, offset linebreaker int 21h mov ah, 9d ;print "HCF of two number is:" mov dx, offset messageB int 21h mov ax,anumber ;copying 2nd number into ax add al,30h ; converting to ascii mov newnumber,al ; copying from low part of register into newnumb mov ah, 2d ;bios code for print a character mov dl, newnumber ;we had saved the ascii code here int 21h ;call to bios JMP exit; exit: mov ah, 4ch int 21h ;exit the program End hi, this is a program that finds highest common factor of 2 different 3digit number. if i put 200, 235,312 (low numbers) it works fine. but if i put 500, 550, 654(bigger number) the program crashes after the 2nd 3digit number is entered. can you help me to find out what problem is?

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  • Delay On Assembler?

    - by Norm
    Hey, I want to know how i can do delay (Timer) on assembler 16 bit on PC. Thank You for helping, Norm. OS: Windows CODE: delay: inc bx cmp bx,WORD ptr[time] je delay2 jmp delay delay2: inc dx cmp dx,WORD ptr[time2] je delay3 jmp delay mov bx,0 delay3: inc cx cmp cx,WORD ptr[time3] je Finish_delay jmp delay its not work good i need less complicated code

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  • invalid effective address calculation!

    - by Zia ur Rahman
    Hay Dear! Please look at the following program, the error is invalid effective address calculation and i have mentioned that line please tell me why its invalid effective address calculation here is the program [org 0x100] jmp start array1: dw 10,15,20,25,30,35,40,45,50,55 array2: dw 15,10,20,35,40,30,55,50,25,45 start: mov bx,0 mov dx,0 loop: mov ax,[array2+bx] cmp ax,[array1+cx]//here is the error invalid effective address calculation jne NextElementOfArray1 NextElementOfArray2: add bx,2 cmp bx,20 je end mov cx,0 jmp loop NextElementOfArray1: add cx,2 cmp cx,20 je NextElementOfArray2 jmp loop end: mov ax,0x4c00 int 0x21

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  • Throwing a C++ exception after an inline-asm jump

    - by SoapBox
    I have some odd self modifying code, but at the root of it is a pretty simple problem: I want to be able to execute a jmp (or a call) and then from that arbitrary point throw an exception and have it caught by the try/catch block that contained the jmp/call. But when I do this (in gcc 4.4.1 x86_64) the exception results in a terminate() as it would if the exception was thrown from outside of a try/catch. I don't really see how this is different than throwing an exception from inside of some far-flung library, yet it obviously is because it just doesn't work. How can I execute a jmp or call but still throw an exception back to the original try/catch? Why doesn't this try/catch continue to handle these exceptions as it would if the function was called normally? The code: #include <iostream> #include <stdexcept> using namespace std; void thrower() { cout << "Inside thrower" << endl; throw runtime_error("some exception"); } int main() { cout << "Top of main" << endl; try { asm volatile ( "jmp *%0" // same thing happens with a call instead of a jmp : : "r"((long)thrower) : ); } catch (exception &e) { cout << "Caught : " << e.what() << endl; } cout << "Bottom of main" << endl << endl; } The expected output: Top of main Inside thrower Caught : some exception Bottom of main The actual output: Top of main Inside thrower terminate called after throwing an instance of 'std::runtime_error' what(): some exception Aborted

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  • Slow transfer to external USB3 hard drive

    - by JMP
    Trying to backup data from hard drive before reloading windows following some issue with its load. Having trouble with the file transfer to a USB3/2 external hard drive NTFS. Getting transfer speed of about 116.7kB/sec. In other words its taking about 5 hours to transfer 1.4GB. I've got about 80GB to go. So the transfer is going to take 11days. Seems a little on the slow side. Am I missing something? Is there a way to make this faster. No issue with the external drive transferring this amount in windows. But don't have that option at the moment.

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  • Slow tranfer to external USB3 hard drive

    - by JMP
    Trying to backup data from hard drive before reloading windows following some issue with its load. Having trouble with the file transfer to a USB3/2 external hard drive NTFS. Getting transfer speed of about 116.7kB/sec. In other words its taking about 5 hours to tranfer 1.4GB. I've got about 80GB to go. So the transfer is going to take 11days. Seems a little on the slow side. Am I missing something? Is there a way to make this faster. No issue with the external drive tranferring this amount in windows. But don't have that option at the moment.

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  • Getting to grips with the stack in nasm

    - by MarkPearl
    Today I spent a good part of my day getting to grips with the stack and nasm. After looking at my notes on nasm I think this is one area for the course I am doing they could focus more on… So here are some snippets I have put together that have helped me understand a little bit about the stack… Simplest example of the stack You will probably see examples like the following in circulation… these demonstrate the simplest use of the stack… org 0x100 bits 16 jmp main main: push 42h push 43h push 44h mov ah,2h ;set to display characters pop dx    ;get the first value int 21h   ;and display it pop dx    ;get 2nd value int 21h   ;and display it pop dx    ;get 3rd value int 21h   ;and display it int 20h The output from above code would be… DCB Decoupling code using “call” and “ret” This is great, but it oversimplifies what I want to use the stack for… I do not know if this goes against the grain of assembly programmers or not, but I want to write loosely coupled assembly code – and I want to use the stack as a mechanism for passing values into my decoupled code. In nasm we have the call and return instructions, which provides a mechanism for decoupling code, for example the following could be done… org 0x100 bits 16 jmp main ;---------------------------------------- displayChar: mov ah,2h mov dx,41h int 21h ret ;---------------------------------------- main: call displayChar int 20h   This would output the following to the console A So, it would seem that call and ret allow us to jump to segments of our code and then return back to the calling position – a form of segmenting the code into what we would called in higher order languages “functions” or “methods”. The only issue is, in higher order languages there is a way to pass parameters into the functions and return results. Because of the primitive nature of the call and ret instructions, this does not seem to be obvious. We could of course use the registers to pass values into the subroutine and set values coming out, but the problem with this is we… Have a limited number of registers Are threading our code with tight coupling (it would be hard to migrate methods outside of their intended use in a particular program to another one) With that in mind, I turn to the stack to provide a loosely coupled way of calling subroutines… First attempt with the Stack Initially I thought this would be simple… we could use code that looks as follows to achieve what I want… org 0x100 bits 16 jmp main ;---------------------------------------- displayChar: mov ah,2h pop dx int 21h ret ;---------------------------------------- main: push 41h call displayChar int 20h   However running this application does not give the desired result, I want an ‘A’ to be returned, and I am getting something totally different (you will to). Reading up on the call and ret instructions a discovery is made… they are pushing and popping things onto and off the stack as well… When the call instruction is executed, the current value of IP (the address of the instruction to follow) is pushed onto the stack, when ret is called, the last value on the stack is popped off into the IP register. In effect what the above code is doing is as follows with the stack… push 41h push current value of ip pop current value of ip to dx pop 41h to ip This is not what I want, I need to access the 41h that I pushed onto the stack, but the call value (which is necessary) is putting something in my way. So, what to do? Remember we have other registers we can use as well as a thing called indirect addressing… So, after some reading around, I came up with the following approach using indirect addressing… org 0x100 bits 16 jmp main ;---------------------------------------- displayChar: mov bp,sp mov ah,2h mov dx,[bp+2] int 21h ret ;---------------------------------------- main: push 41h call displayChar int 20h In essence, what I have done here is used a trick with the stack pointer… it goes as follows… Push 41 onto the stack Make the call to the function, which will push the IP register onto the stack and then jump to the displayChar label Move the value in the stack point to the bp register (sp currently points at IP register) Move the at the location of bp minus 2 bytes to dx (this is now the value 41h) display it, execute the ret instruction, which pops the ip value off the stack and goes back to the calling point This approach is still very raw, some further reading around shows that I should be pushing the value of bp onto the stack before replacing it with sp, but it is the starting thread to getting loosely coupled subroutines. Let’s see if you get what the following output would be? org 0x100 bits 16 jmp main ;---------------------------------------- displayChar: mov bp,sp mov ah,2h mov dx,[bp+4] int 21h mov dx,[bp+2] int 21h ret ;---------------------------------------- main: push 41h push 42h call displayChar int 20h The output is… AB Where to from here? If by any luck some assembly programmer comes along and see this code and notices that I have made some fundamental flaw in my logic… I would like to know, so please leave a comment… appreciate any feedback!

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  • How do i implement If statement in Flex/bison

    - by Imran
    Hallo, I need help in flex/bison. Im a beginner in flex/bison, and i hav already looked out these programs and somethings i inderstood, but im learning. My problem is, i want to implement a If-statement via Flex/Bison and i dont know how to start how to do, someone any idea, im very thankful for all your help. here is an example i want to implement: :L1 IF FLAG AND X"0001" EVT 23; ELSE WAIT 500 ms; JMP L1; END IF; how do i implement JMP (jump), when JMP comes it has to jump to the Label L1.

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  • What is required to use LODSB in assembly?

    - by Harvey
    What is the minimum set of steps required to use LODSB to load a relative address to a string in my code? I have the following test program that I'm using PXE to boot. I boot it two ways: via pxelinux.0 and directly. If I boot it directly, my program prints both strings. If I boot via pxelinux.0, it only prints the first string. Why? Working technique (for both): Set the direction flag to increment, cld Set ds to cs Put the address (from start) of string in si Add the starting offset to si Non-working technique (just for pxelinux): Calculate a new segment address based on (((cs << 4) + offset) >> 4) Set ds to that. (either A000 or 07C0) text here to fix bug in markdown // Note: If you try this code, don't forget to set // the "#if 0" below appropriately! .text .globl start, _start start: _start: _start1: .code16 jmp real_start . = _start1 + 0x1fe .byte 0x55, 0xAA // Next sector . = _start1 + 0x200 jmp real_start test1_str: .asciz "\r\nTest: 9020:fe00" test2_str: .asciz "\r\nTest: a000:0000" real_start: cld // Make sure %si gets incremented. #if 0 // When loaded by pxelinux, we're here: // 9020:fe00 ==> a000:0000 // This works. movw $0x9020, %bx movw %bx, %ds movw $(test1_str - _start1), %si addw $0xfe00, %si call print_message // This does not. movw $0xA000, %bx movw %bx, %ds movw $(test2_str - _start1), %si call print_message #else // If we are loaded directly without pxelinux, we're here: // 0000:7c00 ==> 07c0:0000 // This works. movw $0x0000, %bx movw %bx, %ds movw $(test1_str - _start1), %si addw $0x7c00, %si call print_message // This does, too. movw $0x07c0, %bx movw %bx, %ds movw $(test2_str - _start1), %si call print_message #endif // Hang the computer sti 1: jmp 1b // Prints string DS:SI (modifies AX BX SI) print_message: pushw %ax jmp 2f 3: movb $0x0e, %ah /* print char in AL */ int $0x10 /* via TTY mode */ 2: lodsb (%si), %al /* get token */ cmpb $0, %al /* end of string? */ jne 3b popw %ax ret .balign 0x200 Here's the compilation: /usr/bin/ccache gcc -Os -fno-stack-protector -fno-builtin -nostdinc -DSUPPORT_SERIAL=1 -DSUPPORT_HERCULES=1 -DSUPPORT_GRAPHICS=1 -DHAVE_CONFIG_H -I. -Wall -ggdb3 -Wmissing-prototypes -Wunused -Wshadow -Wpointer-arith -falign-jumps=1 -falign-loops=1 -falign-functions=1 -Wundef -g -c -o ds_teststart_exec-ds_teststart.o ds_test.S /usr/bin/ccache gcc -g -o ds_teststart.exec -nostdlib -Wl,-N -Wl,-Ttext -Wl,8000 ds_teststart_exec-ds_teststart.o objcopy -O binary ds_teststart.exec ds_teststart

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  • MSBuild (.NET 4.0) access problems

    - by JMP
    I'm using Cruise Control .NET as my build server (Windows 2008 Server). Yesterday I upgraded my ASP.NET MVC project from VS 2008/.NET 3.5 to VS 2010/.NET 4.0. The only change I made to my ccnet.config's MSBuild task was the location of MSBuild.exe. Ever since I made that change, the build has been broken with the error: MSB4019 - The imported project "C:\Program Files (x86)\MSBuild\Microsoft\VisualStudio\v10.0\WebApplications\Microsoft.WebApplication.targets" was not found. Confirm that the path in the declaration is correct, and that the file exists on disk. This file does, in fact, exist in the location specified (I solved a problem similar to this when setting up the build server for VS2008/.NET 3.5 by copying the files from my dev environment to my build environment). So I RDP'ed into the build machine and opened a command prompt, used MSBUILD to attempt to build my project. MSBUILD returns the error: MSB3021 - Unable to copy file "obj\debug....dll". Access to the path 'bin....dll' is denied. Since I'm running MSBUILD from the command prompt, logged in with an account that has administrative privileges, I'm assuming that MSBUILD is running with the same privileges that I have. Next, I tried to copy the file that MSBUILD was attempting to copy. In this case, I get the UAC dialog that makes me click the [Continue] button to complete the copy. I'd like to avoid installing Visual Studio 2010 on my build machine, can anyone suggest other fixes I might try?

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  • C++ class with char pointers returning garbage

    - by JMP
    I created a class "Entry" to handle Dictionary entries, but in my main(), I create the Entry() and try to cout the char typed public members, but I get garbage. When I look at the Watch list in debugger, I see the values being set, but as soon as I access the values, there is garbage. Can anyone elaborate on what I might be missing? #include <iostream> using namespace std; class Entry { public: Entry(const char *line); char *Word; char *Definition; }; Entry::Entry(const char *line) { char tmp[100]; strcpy(tmp, line); Word = strtok(tmp, ",") + '\0'; Definition = strtok(0,",") + '\0'; } int main() { Entry *e = new Entry("drink,What you need after a long day's work"); cout << "Word: " << e->Word << endl; cout << "Def: " << e->Definition << endl; cout << endl; delete e; e = 0; return 0; }

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  • How can I handle maxRequestLength exceptions elegantly?

    - by JMP
    In my ASP.NET MVC (v2 if it matters) app, I have a page that allows the user to upload a file. I've configured the maxRequestLength for my app to allow files up to 25MB. As a test, I send it a 500MB file which throws the exception: Maximum request length exceeded. (I only know this because ELMAH catches the error and logs it.) In my web.config, I've set customErrors mode="On" with a defaultRedirect, but the user isn't redirected at all, they don't even get a yellow-screen-of-death. In Chrome, for example, you'll see the error: Error 101 (net::ERR_CONNECTION_RESET): Unknown error. Is it possible to provide a more elegant user experience for this situation?

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  • Attempting to convert an if statement to assembly

    - by Malfist
    What am I doing wrong? This is the assmebly I've written: char encode(char plain){ __asm{ mov al, plain ;check for y or z status cmp al, 'y' je YorZ cmp al, 'z' je YorZ cmp al, 'Y' je YorZ cmp al, 'Z' je YorZ ;check to make sure it is in the alphabet now mov cl, al sub cl, 'A' cmp cl, 24 jl Other sub cl, '6' ;there are six characters between 'Z' and 'a' cmp cl, 24 jl Other jmp done ;means it is not in the alphabet YorZ: sub al, 24 jmp done Other: add al, 2 jmp done done: leave ret } } and this is the C code it's supposed to replace, but doesn't char encode(char plain){ char code; if((plain>='a' && plain<='x') || (plain>='A' && plain <='X')){ code = plain+2; }else if(plain == 'y' || plain=='z' || plain=='Y' || plain == 'y'){ code = plain - 24; }else{ code = plain; } return code; } It seems to convert every character that isn't an y,z,Y,Z into a plus 2 equivalent instead of just A-Xa-x. Any ideas why?

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  • Am I Writing Assembly Or NASM?

    - by cam
    I'm fed up with this. I've been trying to just get a grip on assembly for awhile, but I feel like I'm coding towards my compiler rather than a language. I've been using this tutorial, and so far it's giving me hell. I'm using NASM, which may be the problem, but I figured it was the most popular one. I'm simply trying to learn the most general form of assembly, so I decided to learn x86. I keep running into stupid errors, like not being able to increment a variable. Here's the latest one: not being able to use div. mov bx, 0; mov cx, 0; jmp start; start: inc cx; mov ax, cx; div 3; <-- invalid combination of opcode and operand cmp ah,0; jz totalvalue; mov ax, cx; div 5; <-- invalid combination of opcode and operand cmp ah, 0; jz totalvalue; cmp cx, 1000; jz end; totalvalue: add bx,cx; jmp start; jmp end; end: mov ah,4ch; mov al,00; int 21h; Should I change compilers? It seems like division should be standard. Do I need to read two tutorials (one on NASM, and one on x86?). Any specific help on this problem?

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