5 replies

Segmentation Fault in C Function Printing Double from Assembly Code

I'm encountering a

segmentation fault

segmentation fault

while calling a

function from assembly code to print floating point values. The

function employs a switch statement to handle different data types, including doubles.
Been able to confirm that the issue lies within the

printf

printf

function when handling

double values

double values

, as converting the

double

double

to an

integer

integer

before printing works correctly. But directly printing the

double

double

using

%f

%f

results in a segmentation fault.
I'm running this on a 64 bit system (Ubuntu 22.04) and the GCC compiler.

Any insights into resolving this issue ?

Solution

@Marvee Amasi It sounds like you’re dealing with an

alignment

alignment

issue or possibly an issue with how the

double

double

is being accessed in

memory

memory

. When you cast a

long

long

to a

double

double

, there’s a chance that the

address

address

isn’t properly

aligned

aligned

for accessing

double-precision floating

double-precision floating

point numbers, especially on a

64-bit system

64-bit system

.

A quick test would be to ensure that

val

val

is aligned correctly before casting it to a

double

double

. You can add an

assertion

assertion

to check the

alignment

alignment

case 6:
  assert(val % sizeof(double) == 0);  // Ensure alignment
  c = *(double*) val;
  printf("%f\n", c); /* seg fault */
  break;

case 6:
  assert(val % sizeof(double) == 0);  // Ensure alignment
  c = *(double*) val;
  printf("%f\n", c); /* seg fault */
  break;

If the

assertion

assertion

fails, then the

address

address

val

val

isn’t properly

aligned

aligned

for a

double

double

, which would cause the

segmentation

segmentation

fault.

Also, consider checking how the value of

val

val

is being

passed

passed

from the

assembly code

assembly code

. If there's any chance that it’s being

misaligned

misaligned

before it’s passed to the

function.

Jump to solution

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5 replies

Marvee Amasi

Segmentation Fault in C Function Printing Double from Assembly Code

I'm encountering a

segmentation fault

segmentation fault

while calling a

function from assembly code to print floating point values. The

function employs a switch statement to handle different data types, including doubles.
Been able to confirm that the issue lies within the

printf

printf

function when handling

double values

double values

, as converting the

double

double

to an

integer

integer

before printing works correctly. But directly printing the

double

double

using

%f

%f

results in a segmentation fault.
I'm running this on a 64 bit system (Ubuntu 22.04) and the GCC compiler.

Any insights into resolving this issue ?

Solution

@Marvee Amasi It sounds like you’re dealing with an

alignment

alignment

issue or possibly an issue with how the

double

double

is being accessed in

memory

memory

. When you cast a

long

long

to a

double

double

, there’s a chance that the

address

address

isn’t properly

aligned

aligned

for accessing

double-precision floating

double-precision floating

point numbers, especially on a

64-bit system

64-bit system

.

A quick test would be to ensure that

val

val

is aligned correctly before casting it to a

double

double

. You can add an

assertion

assertion

to check the

alignment

alignment

case 6:
  assert(val % sizeof(double) == 0);  // Ensure alignment
  c = *(double*) val;
  printf("%f\n", c); /* seg fault */
  break;

case 6:
  assert(val % sizeof(double) == 0);  // Ensure alignment
  c = *(double*) val;
  printf("%f\n", c); /* seg fault */
  break;

If the

assertion

assertion

fails, then the

address

address

val

val

isn’t properly

aligned

aligned

for a

double

double

, which would cause the

segmentation

segmentation

fault.

Also, consider checking how the value of

val

val

is being

passed

passed

from the

assembly code

assembly code

. If there's any chance that it’s being

misaligned

misaligned

before it’s passed to the

function.

Jump to solution

Segmentation Fault in C Function Printing Double from Assembly Code

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