Section Exercises
Last updated
Last updated
printf takes only one argument which represents the memory address of the first byte of a string.False!
printf takes a variable number of arguments depending on how many format specifiers are in your string (if you want to deepen you knowledge regarding the printf functionality try ). More important, the first argument is always the format string.
scanf takes a variable number of arguments, the first one being a format string.True!
Note: Because of this, for scanf, the number of vector registers specified in the al registers will be 0.
scanf are needed throughout the program/subroutines.False!
The base pointer relative addressing is useful in this case. Stack pointer relative addressing is useful for values used once or for a short period of time.
False!
Base pointer relative addressing is useful when the value of a variable is needed throughout a program/subroutine.
True!
Stack pointer relative addressing is useful when the value should only be stored on the stack until it can be moved to registers for further usage, so for values that are only used once or for a short time.
The following assembly code shows a correct usage of scanf:
.text
.input: .asciz "%d"
main:
# prolog
subq $8, %rsp
# ...
leaq input(%rip), %rsi
leaq -8(%rbp), %rdi
movb $0, %al
call scanfFalse!
The first argument of scanf, stored in rdi, is the address of the string/format that it will read and the second argument, stored in rsi, is the location on the stack where the read value will be stored. Moreover, regarding calling conventions, the stack is misaligned as we only subtract 8 from rsp instead of 16 or a multiple of 16.
movq $0, %al instead of movb $0, %al.False!
In the register section, we saw that the name of the register can indicate its size and location. In this case, al stores 8 bits (1 byte), so we need to use movb to indicate that we move one byte.
Which directive tells the assembler that a string should be placed in a text section as ASCII-encoded characters?
.ascizCorrect!
The .asciz directive indicates that a string should be placed in a text section as ASCII-encoded characters, but it also indicates the fact that the string will be followed by a zero byte.
.textWrong!
The .text directive specifies that the following line should be placed in the text section of the program, but does not indicate the type or encoding of the content of the line.
.equWrong!
The .equ directive can be used to define symbolic names for expressions, such as numeric constants.
Which format specifiers indicate a signed long, a zero-terminated string and hexadecimal integer?