CPU Architecture and Alignment

Do different CPU architectures handle alignment differently?

Yes, different CPU architectures have varying alignment requirements and behaviors. Let's look at some key differences:

x86/x64 (Intel/AMD)

Modern x86 processors are relatively forgiving:

#include <iostream>

#pragma pack(1)
struct Misaligned {
  char A;
  int B;
};
#pragma pack()

int main() {
  Misaligned Data{'X', 42};
  // On x86/x64: Works, but slower
  std::cout << Data.B << "\n";
}

ARM

ARM processors are stricter about alignment:

#include <iostream>

#pragma pack(1)
struct Misaligned {
  char A;
  int B;
} Data{'X', 42};
#pragma pack()

int main() {
  // On older ARM: May cause hardware exception!
  // On newer ARM: May trigger alignment fault handler
  std::cout << Data.B << "\n";
}

RISC Architectures

RISC processors often have strict alignment rules:

#include <iostream>

struct AlignmentMatters {
  // On RISC:
  short Value;// Must be 2-byte aligned
  int Data;// Must be 4-byte aligned
  double Price;// Must be 8-byte aligned
};

int main() {
  std::cout << "Size on RISC: "
    << sizeof(AlignmentMatters) << "\n";
}

To write portable code that works across architectures:

  • Let the compiler handle alignment
  • Don't use #pragma pack unless absolutely necessary
  • Test on different platforms when possible
  • Use standard C++ serialization when sharing data
  • Be extra careful with embedded systems

The key takeaway is that while modern PC architectures handle misalignment gracefully (with performance penalties), other platforms may be less forgiving. Writing properly aligned code ensures maximum portability.

Padding and Alignment

Learn how memory alignment affects data serialization and how to handle it safely

Questions & Answers

Answers are generated by AI models and may not have been reviewed. Be mindful when running any code on your device.

Why Computer Memory Needs Padding
Why do we need padding at all? Can't the computer just read the bytes it needs?
Consequences of Misaligned Memory
What happens if we try to read memory that isn't properly aligned?
Memory Impact of Padding
Does padding waste a lot of memory in real programs?
Understanding Natural Alignment
How do I know what the natural alignment of a type should be?
Alignment with Virtual Functions
How does alignment work with inheritance and virtual functions?
Understanding Union Alignment
How does alignment work with unions?
SIMD and Memory Alignment
How does alignment work with SIMD instructions?
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