Stack Overflow
Stack Overflow

Questions tagged [opcode]

The binary number that represents a machine instruction for a specific processor type.

An Opcode is the binary number that represents a machine instruction for a specific processor type.

Use this tag only for questions specific to the binary representation of machine instructions. Do not use this tag for general assembly language questions.

470 questions
242
votes
4 answers

What does a \ (backslash) do in PHP (5.3+)?

What does a \ do in PHP? For example, CSRF4PHP has \FALSE, \session_id, and \Exception: public function __construct($timeout=300, $acceptGet=\FALSE){ $this->timeout = $timeout; if (\session_id()) { $this->acceptGet = (bool)…
Alfred
  • 60,935
  • 33
  • 147
  • 186
80
votes
4 answers

How to get opcodes of PHP?

Its opcode is: 1:
Mask
  • 33,129
  • 48
  • 101
  • 125
46
votes
3 answers

Unintuitive expression evaluation with incrementation

For the following code
Daniel
  • 7,684
  • 7
  • 52
  • 76
41
votes
7 answers

Intel x86 Opcode Reference?

What is a relatively quick and easy method of looking up what an arbitrary opcode means (say, 0xC8) in x86? The Intel Software Developer's manual isn't very fun to search through...
user541686
  • 205,094
  • 128
  • 528
  • 886
34
votes
2 answers

What is the purpose of the ACC_SUPER access flag on Java Class files?

The invokespecial JVM instruction is used for calling initialisation methods () when creating new objects. The description of the instruction suggests (but doesn't clarify) that the decision on whether to call the constructor of a superclass…
Jivings
  • 22,834
  • 6
  • 60
  • 101
33
votes
2 answers

How does a class extension or Interface work?

Have come across this so many times and am not sure why so it got me curious. Some classes work before they are declared and others don't; Example 1 $test = new TestClass(); // top of class class TestClass { function __construct() { …
Baba
  • 94,024
  • 28
  • 166
  • 217
32
votes
4 answers

Is stack in CPU or RAM?

I have a few question about stack. Is stack in CPU or RAM? Is stack a place to run OPcode? Is EIP in CPU or RAM?
abiati madana
  • 331
  • 1
  • 3
  • 3
31
votes
6 answers

Translation of machinecode into LLVM IR (disassembly / reassembly of X86_64. X86. ARM into LLVM bitcode)

I would like to translate X86_64, x86, ARM executables into LLVM IR (disassembly). What solution do you suggest ?
Grzegorz Wierzowiecki
  • 10,545
  • 9
  • 50
  • 88
31
votes
3 answers

Processing ELF relocations - understanding the relocs, symbols, section data, and how they work together

TL;DR I tried to make this a short question but it's a complicated problem so it ended up being long. If you can answer any part of this or give any suggestions or tips or resources or anything at all, it would be extremely helpful (even if you…
thehelix
  • 578
  • 1
  • 6
  • 10
30
votes
2 answers

Avoiding getfield opcode

In Java's String class, the trim method contains this: int off = offset; /* avoid getfield opcode */ char[] val = value; /* avoid getfield opcode */ I'm a bit puzzled by the comment "avoid getfield opcode"... What does this mean? (I take it…
SyntaxT3rr0r
  • 27,745
  • 21
  • 87
  • 120
27
votes
3 answers

How to check if APC opcode cache is working fine in PHP?

I am using PHP with APC cache enabled: apc.cache_by_default => On apc.enabled => On apc.ttl => 7200 Now how can I know if it is using the opcode cache 100%. For example, let us say that I have this PHP file: Now after…
Lina
  • 2,090
  • 4
  • 20
  • 23
23
votes
4 answers

VM Design: More opcodes or less opcodes? What is better?

Don't be shocked. This is a lot of text but I'm afraid without giving some detailed information I cannot really show what this is all about (and might get a lot of answers that don't really address my question). And this definitely not an assignment…
Mecki
  • 125,244
  • 33
  • 244
  • 253
20
votes
2 answers

execute binary machine code from C

following this instructions I have managed to produce only 528 bytes in size a.out (when gcc main.c gave me 8539 bytes big file initially). main.c was: int main(int argc, char** argv) { return 42; } but I have built a.out from this assembly…
4pie0
  • 29,204
  • 9
  • 82
  • 118
18
votes
2 answers

Is there an x86 opcode for moving an immediate byte to a direct memory location (without using registers)?

Is there a way to 'mov'e a specific immediate byte-size number into a direct memory location? I.e. MOV 10h,ffffh to write the value 16 into the memory address 65535? If so, which opcode is that, orwould I have to store a memory address into a…
Nicholas Hill
  • 191
  • 1
  • 2
  • 4
18
votes
3 answers

Optimize APC Caching

here is a link to how my APC is running : [removed] As you can see, it fills up pretty quickly and my Cache Full Count goes over 1000 sometimes My website uses Wordpress. I notice that every time I make a new post or edit a post, 2 things happen.…
GreatestSwordsman
  • 1,175
  • 5
  • 20
  • 39
1
2 3
…
31 32