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Computer systems

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Assume that x is a double variable and that f is a pointer to a function taking a double and returning a double.

Tick all the possible calls to f.

Penalty for wrong ticks.

x = f(*x);

None of these calls is possible.

What does the following code print?

#include <stdio.h>
#include <string.h>
void f(char* string)
{
  const size_t size = strlen(string);
  if (size >= 8) string[7] = '\0';
  if (size >= 5) string[4] = 'a';
  puts(string);
}
int main(void) 
{
  f("How qre you?");
  return 0;
}

Howaqr0 you?

Howaqre0you?

Nothing (but an error message) because the code does not run properly (e.g. Segmentation Fault).

Nothing because the code does not compile.

Howaqre

100%

Something else than the other proposals.

How qre

How are you?

How are

How qre0you?

How are0you?

How qre you?

Howaqre you?

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What is the correct way to define a type funct to point to a function taking a pointer to an int

an returning a pointer to an int?

None of the others

typedef int* *funct(int*);

typedef int* funct*(int*);

typedef *int (*funct)(*int);

typedef int*(*funct)(int*);

100%

typedef *int funct*(*int);

typedef (int*) *funct(int*);

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We want to write a generic function that can add all the elements of an array (of unknown type, e.g. real numbers, complex numbers, vectors, matrices, ...) and get the result of the sum (of unknown type), either as a return value or passed by reference (then returning some error code).

What are the possible prototypes for such a function?

Penalty for wrong ticks.

double add_all(void* tab, size_t el_size, size_t nb_el, double (*add_element)(void*, void*));

void* add_all(void* tab, size_t el_size, void* (*add_element)(void*, void*));

100%

int add_all(void* tab, size_t el_size, size_t nb_el, void* (*add_element)(void*, void*), void** result);

100%

void* add_all(void* tab, void* (*add_element)(void*, void*));

100%

void* add_all(void* tab);

void* add_all(void* tab, size_t el_size, size_t nb_el, void* (*add_element)(void*, void*));

100%

double add_all(void* tab, size_t el_size, size_t nb_el, void* (*add_element)(void*, void*));

void* add_all(void* tab, size_t el_size, size_t nb_el);

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Select all the correct statements about a void* variable.

Penalty for wrong ticks.

It can point to any type.

100%

It cannot be used.

It is useless.

It does not require any explicit casting to be assigned to another pointer.

100%

It can point only into the heap.

It can point only into the stack.

It is always NULL.

It cannot exist in C (invalid C).

It does not point anywhere.

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Consider a system that uses paging. Which of the following statements are true?

Many may be true.

If a process references a page that is currently stored on disk, the process makes a read syscall to read the page from disk.

The MMU knows whether a page is present in physical memory or not thanks to the "present" bit in page-table entries.

100%

If the memory images of all the processes do not fit in main memory, some pages are temporarily stored on disk.

100%

If a process references a page that is currently stored on disk, the MMU triggers a page fault, which causes the OS to map the page to a frame in physical memory.

100%

If the memory image of a new process does not fit in physical memory, the process is always terminated by the OS.

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Which of the following statements about the Table Look-aside Buffer (TLB) are true?

Many answers may be correct.

Without the TLB, some addresses would be correctly translated but others not.

Without the TLB, address translation would be significantly slower.

100%

The TLB caches the results of the most recently/frequently performed address translations.

100%

Without the TLB, address translation would not work.

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Which of the following statements are true?

Many may be true.

A multi-level page table enables faster address translation than a linear page table.

100%

A linear page table can map more memory addresses than a multi-level page table.

A multi-level page table consumes more space than a linear page table.

A multi-level page table consumes less space than a linear page table.

100%

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[Don't be alarmed if this question feels hard. Just try your best.]

This is the complete page table of a process:

Page 0 ---> Frame 0

Page 1 ---> Frame 10

Page 2 ---> Frame 3

Page 3 ---> Frame 203

Page 4 ---> Frame 127

Page 5 ---> Frame 67

Page 6 ---> Frame 84

Page 7 ---> Frame 16

Assume that these pages cover the entire virtual address space of the process.

Which of the following statements are certainly true about the system where this process belongs?

Many may be certainly true.

The 3 most significant bits of a virtual memory address represent the virtual page number.

100%

The 4 least significant bits of a virtual memory address represent the offset.

100%

Virtual memory address 0b0 maps to physical memory address 0b0.

100%

Virtual memory address 0b1 maps to physical memory address 0b1010.

100%

The 6 most significant bits of a physical memory address represent the frame number.

100%

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[Don't be alarmed if this question feels hard. Just try your best.]

Consider a system where each virtual memory address consists of:

A 10-bit virtual page number.
A 6-bit page offset number.

Which of the following statements are true?

Many may be true.

Each process can have 2^10 = 1024 pages.

100%

Each page fits 2^6 = 64 bytes.

100%

Each frame fits 2^6 = 64 bytes.

100%

Virtual memory address 0b1000000001100001 may map to physical memory address 0b1100101101111000.

100%

Virtual memory address 0b0 necessarily maps to physical memory address 0b0.

100%

Virtual memory address 0b1 necessarily maps to the second byte of a frame.

100%

Each process's memory image must fit within 2^6=64 bytes.

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