65
votes
3
answers
3K
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How do you use gcc to generate assembly code in Intel syntax?
The gcc -S option will generate assembly code in AT&T syntax, is there a way to generate files in Intel sy
66
votes
13
answers
1.7K
views
Can num++ be atomic for 'int num'?
In general, for int num, num++ (or ++num), as a read-modify-write operation, is not atomic. But I often see co
54
votes
4
answers
2K
views
What are the calling conventions for UNIX & Linux system calls (and user-space functions) on i386 and x86-64
Following links explain x86-32 system call conventions for both UNIX (BSD flavor) & Linux: http://www.int
50
votes
3
answers
1.8K
views
Why does GCC generate such radically different assembly for nearly the same C code?
While writing an optimized ftol function I found some very odd behaviour in GCC 4.6.1. Let me show you the cod
64
votes
21
answers
380
views
Is inline assembly language slower than native C++ code?
I tried to compare the performance of inline assembly language and C++ code, so I wrote a function that add tw
66
votes
24
answers
1.4K
views
Protecting executable from reverse engineering?
I've been contemplating how to protect my C/C++ code from disassembly and reverse engineering. Normally
56
votes
4
answers
3K
views
Why would introducing useless MOV instructions speed up a tight loop in x86_64 assembly?
Background: While optimizing some Pascal code with embedded assembly language, I noticed an unnecessary MOV i
62
votes
5
answers
2.5K
views
Why does GCC use multiplication by a strange number in implementing integer division?
I've been reading about div and mul assembly operations, and I decided to see them in action by writing a
62
votes
10
answers
2.4K
views
Assembly code vs Machine code vs Object code?
What is the difference between object code, machine code and assembly code? Can you give a visual example of
53
votes
7
answers
1.5K
views
What is exactly the base pointer and stack pointer? To what do they point?
Using this example coming from wikipedia, in which DrawSquare() calls DrawLine(), (Note that this diagram h
49
votes
12
answers
1.4K
views
Is 'switch' faster than 'if'?
Is a switch statement actually faster than an if statement? I ran the code below on Visual Studio 2010's
50
votes
3
answers
1.7K
views
What is a retpoline and how does it work?
In order to mitigate against kernel or cross-process memory disclosure (the Spectre attack), the Linux kernel1
54
votes
10
answers
1.6K
views
What does multicore assembly language look like?
Once upon a time, to write x86 assembler, for example, you would have instructions stating "load the EDX regis
58
votes
16
answers
655
views
Is it possible to "decompile" a Windows .exe? Or at least view the Assembly?
A friend of mine downloaded some malware from Facebook, and I'm curious to see what it does without infec
63
votes
5
answers
1.7K
views
Why does Java switch on contiguous ints appear to run faster with added cases?
I am working on some Java code which needs to be highly optimized as it will run in hot functions that are inv
48
votes
10
answers
1.6K
views
Using GCC to produce readable assembly?
I was wondering how to use GCC on my C source file to dump a mnemonic version of the machine code so I could s
55
votes
17
answers
1.5K
views
How do you get assembler output from C/C++ source in gcc?
How does one do this? If I want to analyze how something is getting compiled, how would I get the emitted ass
52
votes
4
answers
663
views
How do I achieve the theoretical maximum of 4 FLOPs per cycle?
How can the theoretical peak performance of 4 floating point operations (double precision) per cycle be achiev
58
votes
11
answers
1.9K
views
Why does C++ code for testing the Collatz conjecture run faster than hand-written assembly?
I wrote these two solutions for Project Euler Q14, in assembly and in C++. They implement identical brute forc
64
votes
11
answers
1.9K
views
Replacing a 32-bit loop counter with 64-bit introduces crazy performance deviations with _mm_popcnt_u64 on Intel CPUs
I was looking for the fastest way to popcount large arrays of data. I encountered a very weird effect: Changin
