5.7 · exercise

Practice: Mental Memory Tracing

Act as the CPU. Trace the memory addresses and register states through these AArch64 snippets.

0 of 10 correct

mov x20, 0x1000
ldr x21, [x20, 16]!

What is the exact hex address stored inside register x20 AFTER this code executes?

mov x28, 0x2000
str w20, [x28], 8

What exact hex memory address does the 'str' instruction write to?

mov x28, 0x2000
str w20, [x28], 8

What is the exact hex address stored inside register x28 AFTER this code executes?

mov x21, 5
ldr x22, [x29, x21, LSL 3]

What exact decimal offset is ultimately added to x29 to calculate the memory address?

add sp, sp, -28 & -16

What exact decimal integer is ultimately added to the Stack Pointer by the assembler?

fp .req x29
c_s = -4
add sp, sp, -4 & -16
mov w21, 10
str w21, [fp, c_s]

Is the variable 'c' stored above (higher address) or below (lower address) the frame record in memory?

main: stp x29, x30, [sp, -(16 + 12) & -16]!

How many total decimal bytes are allocated on the stack by this instruction?

main: stp x29, x30, [sp, -32]!

How many 'pad bytes' (unused bytes) exist in this specific stack frame if only three 4-byte integers are stored as local variables?

ldrsb w20, [x29]
// Address holds the byte 0xFF

If the byte 0xFF (-1 in 8-bit signed) is loaded, what is the exact hex value of w20 after execution?

ldrb w20, [x29]
// Address holds the byte 0xFF

If the byte 0xFF is loaded using ldrb, what is the exact hex value of w20 after execution?