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Editorial Team
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Asked: 2026-05-20T07:28:44+00:00

This question is not about any error I’m currently seeing, it’s more about theory

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This question is not about any error I’m currently seeing, it’s more about theory and getting educated on the variations in HW architecture design and implementation.

Scenario 1: Assuming a 16-bit processor with 16-bit registers, 16-bit addressing, and sizeof(int) = 16 bits:

unsigned int a, b, c, d;
a=0xFFFF;
b=0xFFFF;
c=a+b;

Is it possible for the memory location next to c to be overwritten?
(In this case I would expect that an overflow flag would be raised during the add operation, and c either remain unchanged or be filled with undefined data.)

Scenario 2: Assuming a 32-bit processor with 32-bit registers, 32-bit addressing, sizeof(int) = 32 bits, and sizeof(short int)=16 bits:

unsigned int a, b;
unsigned short int c, d;
a=0xFFFF;
b=0xFFFF;
c=a+b;

Is it possible for the memory location next to c to be overwritten?
(I would expect that no overflow flag be raised during the add operation, but whether or not a memory access or overflow flag be raised during the assignment operation would depend on the actual design and implementation of the HW. If d was located in the upper 16 bits of the same 32-bit address location (probably not even possible with 32-bit addressing), it might be overwritten.)

Scenario 3: Assuming a 32-bit processor with 32-bit registers, 16-bit addressing, sizeof(int) = 32 bits, and sizeof(short int)=16 bits:

unsigned int a, b;
unsigned short int c, d;
a=0xFFFF;
b=0xFFFF;
c=a+b;

Is it possible for the memory location next to c to be overwritten?
(I would expect some overflow flag or memory violation flag to be raised during the type conversion and assignment operation.)

Scenario 4: Assuming a 32-bit processor with 32-bit registers, 32-bit addressing, and sizeof(int) = 32 bits:

unsigned int a, b;
struct {
    unsigned int c:16;
    unsigned int d:16;
} e;
a=0xFFFF;
b=0xFFFF;
e.c=a+b;

Is it possible for the memory location next to c, namely d, to be overwritten? (In this case, since c and d are expected to reside in the same 32-bit address and both are technically 32-bit integers, it’s conceivable that no overflow flags be raised during addition or assignment, and d could be affected.)

I have not tried to test this on actual hardware because my question is more about theory and possible variations in design and implementation. Any insight would be appreciated.

  • Is it possible for a binary integer operation that results in an overflow to overwrite adjacent memory?
  • Are there currently any HW implementations that suffer from similar memory overwrite problems, or have there been systems in the past that had this problem?
  • What devices do typical processors use to guard against neighboring memory from being overwritten by arithmetic and assignment operations?
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1 Answer

  1. Editorial Team

    The addition operation is processed inside the processor afaik, so whatever you do, the add operation will be done inside the CPU (in the ALU more precisely)
    The overflow register would be set in case of overflow, and the result will still be in the register, and then copied back to your memory location without risk of corrupting adjacent memory.
    This is how the code would (sort of) be translated in asm: 

    mov ax, ptr [memory location of a]
mov bx, ptr [memory location of b]
add ax,bx
mov ptr [memory location of c], ax

    so as you can see, c would only hold what was in ax (which is of a known and fixed size) no matter if an overflow occurred or not

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