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Author: Admin | 2025-04-27
Integer offset.Critically, trying to run code within a non-code segment, read code as data, access a non-existent address, or similar action, can lead to a Segmentation fault, which is irrecoverable. In short, this means the program tries to access data outside of the segment where that data resides because a base-pointer combination goes outside the respective segment size. Due to this critical misbehavior, the kernel kills the program.3. Example 0xbadc0deTo demonstrate, we compile a minimal executable file that causes a segmentation fault.3.1. Write CodeFirst, we create a simple C file:$ cat segfault.cint main() { int *address = 0; *address = 666; return 0;}Here, we have a standard main() function, which [return]s 0 upon success. However, the first two lines of code in the main function are of interest in this case:int *address = 0; declares a * pointer to an [int]eger variable at address 0*address = 666; attempts to assign the value 666 to the address (0) pointed to by the pointer variable addressNow, we can create a binary file from this code.3.2. Compile Binary ExecutableAt this point, let’s compile an executable binary from segfault.c via gcc:$ gcc -O0 -s -nostdlib --entry main segfault.c -o segfault.binTo minimize the footprint of our resulting file, we use a number of options:-O0: 0 [O]ptimizations, meaning the compiler doesn’t attempt any special handling of the code-s: omit symbol tables and relocation information-nostdlib: no linking to the standard library, since we don’t use any standard library functions or optimizations–entry main: assume the address of main() as the program –entry pointImportantly, we minimize and simplify the final binary executable file for clarity when debugging later.3.3. Run Binary ExecutableAfter writing and compiling our code, let’s run the resulting executable:$ ./segfault.binSegmentation faultAs expected, we get a Segmentation fault. Basically, the attempt to assign a value to the cell
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