Hard to understand GCC assembly instructions to calculate conditional jump

Hard to understand GCC assembly instructions to calculate conditional jump

By : user2949264
Date : November 16 2020, 06:23 AM
I hope this helps . It's jge because the compiler swapped both the operands and the condition. It's doing global_count >= a. Notice that 0x10(%ebp) is a and %eax is global_count. To complicate matters further, at&t syntax itself has operands reversed.
code :

Share : facebook icon twitter icon
Conditional Jump instructions?

Conditional Jump instructions?

By : Jim Lu
Date : March 29 2020, 07:55 AM
hope this fix your issue
Many processors have conditional jump instructions only for conditional jumps with a limited range. For example, the target of the jump may not be further than 128 bytes away from the current program counter.
code :
jnz distant_label
[other instructions]
jz nearby_label
jmp distant_label
[other instructions]
What are the conditional jump instructions for Go's assembler?

What are the conditional jump instructions for Go's assembler?

By : user3616206
Date : March 29 2020, 07:55 AM
wish help you to fix your issue I'm answering this so I don't lose the information, and so other people don't have to go through the same sleuthing game as me. Looking at optab.c and the x86 jumps we can match up the instruction encodings to solve the puzzle.
code :
JCS     JB
JGT     JG
JHI     JA
JLT     JL
JMI     JS
JOS     JO
x86 Assembly two jump instructions with the same target

x86 Assembly two jump instructions with the same target

By : Jacob
Date : March 29 2020, 07:55 AM
I wish did fix the issue. The result of assembly code compilation is a piece of native code, more specifically a sequence of bytes, where different parts of this sequence correspond to instructions from the original assembly. Intel x86 processors have a so-called CISC instruction set, which basically means that instruction length in bytes can vary from 1 to some 12, and that's without considering instruction set extensions that are available nowadays. The technique presented makes use of this fact.
The whole point is to mislead the person with a potential mischief in their mind. Code of the second example (with pop eax and retn) is what we want to execute and what will be executed. However, because we inserted a fake byte in front of the pop eax instruction, disassembled code will without paying close attention appear as if there was a call to some location in memory, since most of the less bright disassemblers automatically assume that machine code of a binary has no gaps in it.
difference between conditional instructions (cmov) and jump instructions

difference between conditional instructions (cmov) and jump instructions

By : ap-2
Date : March 29 2020, 07:55 AM
Hope that helps movcc is a so-called predicated instruction. That's fancy-speak for "this instruction executes under a condition (predicate)".
Many processors, including the x86, after doing an arithmetic operation (especially compare instructions), sets the condition code bits to indicate the status of the result of the operation.
How do we use jump in assembly using these instructions?

How do we use jump in assembly using these instructions?

By : somil lohani
Date : March 29 2020, 07:55 AM
help you fix your problem Branching in assembly is flexible, in a sense that you can arrange the code blocks in any order you want. You can also merge the branches by jumping to the same block. To archive this the instructions must to able to jump both forward and backward. The following example shows a use of backward jumping.
code :
073000:  bf 08 00 00 00          mov    edi, 0x8
073005:  31 c0                   xor    eax, eax
073007 <loop>:
073007:  01 f8                   add    eax, edi
073009:  83 ef 01                sub    edi, 0x1
07300c:  75 f9                   jne    073007 <loop>
Unsigned numbers:
0x1234 =  1*16^3 +  2*16^2 + 3*16^1 +  4 = 4660 
0x3420 =  3*16^3 +  4*16^2 + 2*16^1 +  0 = 13344 
0x0A0B =  0*16^3 + 10*16^2 + 0*16^1 + 11 = 2571   (A is 10; B is 11)
0x8000 =  8*16^3 +  0*16^2 + 0*16^1 +  0 = 37268
0xFF7A = 15*16^3 + 15*16^2 + 7*16^1 + 10 = 65402  (F is 15)

Signed numbers:
0x1234 =   ; positive because 1 is smaller than 8
0x3420 =   ; positive because 3 is smaller than 8 
0x0A0B =   ; positive because 0 is smaller than 8
0x8000 =   ; negative because 8 is NOT smaller than 8
0xFF7A =   ; negative because F (15) is NOT smaller than 8

Signed numbers:
0x1234 = 4460  ; positive numbers are calculated like unsigned number
0x3420 = 13344 ; positive numbers are calculated like unsigned number
0x0A0B = 2571  ; positive numbers are calculated like unsigned number
0x8000 = 32768 - 65536 = -32768 ; a simple way to calculate negative number
0xFF7A = 65402 - 65536 = -134 ; a simple way to calculate negative number
Related Posts Related Posts :
  • multiple definition and making sure function is correctly written
  • MD4 openssl core dumped
  • Undefined-Behavior at its best, is it -boundary break? -bad pointer arithmetic? Or just -ignore of aliasing?
  • Why am i getting problem3.c:20:23: error: expected expression before ‘int’?
  • Right Justified Zero filled String in C
  • C Function with parameter without type indicator still works?
  • How to transmit data from an interrupt handler to an user application?
  • Why do I get the error "bash: ./a.out: Permission denied" when I execute a C program in Linux mint 15
  • syntax of sigchld and its declaration
  • error using g_idle_add() in C++, same thing works in C
  • why if else or nested if else are called single statement in C
  • How do I interpret this printf in C
  • load the functions of a shell script without executing it
  • Is FilterSendNetBufferLists handler a must for an NDIS filter to use NdisFSendNetBufferLists?
  • How to write to flash memory using inline assembly?
  • More Return Statements vs. More Indentation
  • How to show an image on a PictureBox from resource?
  • Having malloced some memory,I could't calculator the proper size of the memories I malloced.I don't know why
  • What is the main difference between integer pointer and character pointer?
  • Why are some functions declared extern and header file not included in source in Git source code?
  • what is the use of fflush(stdin) in c programming
  • Is it safe to return file File descriptor locally allocated from another function In C
  • Changing undefined values of an array
  • What does an empty parameter list mean?
  • using strtol on a string literal causing segmentation fault
  • Same structure objects memory overlap?
  • C-Linux-Any way to pass command "history" to Linux shell?
  • Using #define in defining string size C
  • How to use thread pool and message queues in Multithreaded Matrix Multiplication?
  • Can't find how to select path to run a C program
  • Automatic variable in C not initialized but given fixed value within loop
  • main() function defined without return type gives warning
  • Output of following code with integer, float, char variable
  • why buffer memory allocation error in opencl
  • Why am I getting this error during run-time?
  • Strange behaviour of the pow function
  • task in increment , decrement , printf() , why these are evaluated in this manner in C
  • 28 extra bytes in bss
  • Waiting for multiple events without polling
  • Why are my variables reporting as "undeclared identifier" when compiling?
  • Correct AddNode function but somehing happens when I printf
  • When I traverse in the splay tree, then now which one is root?
  • Data type conversion in Postfix evaluation
  • No output in terminal (Head First C)
  • Data writes over after realloc
  • function: findnextchar() doesn't work
  • Getting file-size property from Nautilus
  • Forward declare entities in C standard library?
  • Static array in C
  • Function signature indicates return type void*, but returns pointer of a different type
  • How do I measure time per thread in C?
  • Online judgeProblem (Wrong Answer)
  • Use function pointer initialized in other source file
  • last line of file is duplicated using fscanf
  • How to print files with same month of modification using directory in c?
  • ADT Circular Queue enqueue and dequeue
  • What events can cause ferror to return non-zero?
  • Accessing dynamically allocated structure received through socket
  • Vim with C Conditional Parsing
  • C can pointers be aligned with any other data type?
  • shadow
    Privacy Policy - Terms - Contact Us © ourworld-yourmove.org