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Questions and Answers
What does the term 'caller-saved' imply in a function call?
What does the term 'caller-saved' imply in a function call?
Which of the following registers is classified as callee-saved?
Which of the following registers is classified as callee-saved?
In the context of register usage, which register is responsible for returning values from a function?
In the context of register usage, which register is responsible for returning values from a function?
When a function uses the stack, what must the callee do with its frame pointer?
When a function uses the stack, what must the callee do with its frame pointer?
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Which of the following registers can be modified by the procedure without saving its value first?
Which of the following registers can be modified by the procedure without saving its value first?
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What is the purpose of the %rsp register in a function call?
What is the purpose of the %rsp register in a function call?
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What should a programmer do to ensure the values in the callee-saved registers are preserved across function calls?
What should a programmer do to ensure the values in the callee-saved registers are preserved across function calls?
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In the provided example of a function call, what does the function incr actually do?
In the provided example of a function call, what does the function incr actually do?
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What is the usual restriction on the use of caller-saved registers during a function call?
What is the usual restriction on the use of caller-saved registers during a function call?
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What does the term 'temporary values' refer to in the context of stack memory?
What does the term 'temporary values' refer to in the context of stack memory?
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What is the purpose of the subq $16, %rsp instruction in the call_incr function?
What is the purpose of the subq $16, %rsp instruction in the call_incr function?
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In the call_incr function, what does the movl $3000, %esi instruction accomplish?
In the call_incr function, what does the movl $3000, %esi instruction accomplish?
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What does the leaq 8(%rsp), %rdi instruction do before the function call to incr?
What does the leaq 8(%rsp), %rdi instruction do before the function call to incr?
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What is the significance of the return value stored in %rax after the call instruction?
What is the significance of the return value stored in %rax after the call instruction?
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How does the function incr affect the value of the variable v1?
How does the function incr affect the value of the variable v1?
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What does the addq 8(%rsp), %rax instruction achieve?
What does the addq 8(%rsp), %rax instruction achieve?
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What is implied by the presence of movq $15213, 8(%rsp) in the function?
What is implied by the presence of movq $15213, 8(%rsp) in the function?
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Why is the addq $16, %rsp instruction used before the ret instruction?
Why is the addq $16, %rsp instruction used before the ret instruction?
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What is the role of the stack pointer (%rsp) in x86-64 stack management?
What is the role of the stack pointer (%rsp) in x86-64 stack management?
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Which of the following is true regarding procedure calling conventions on x86-64 architecture?
Which of the following is true regarding procedure calling conventions on x86-64 architecture?
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In the context of function calls, what does the 'call' instruction do?
In the context of function calls, what does the 'call' instruction do?
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What happens to local variables in a stack-based language during function execution?
What happens to local variables in a stack-based language during function execution?
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During a 'push' operation in stack management, which of the following occurs?
During a 'push' operation in stack management, which of the following occurs?
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When returning from a procedure using the 'ret' instruction, what is executed?
When returning from a procedure using the 'ret' instruction, what is executed?
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What is a characteristic of stack-based languages regarding function calls?
What is a characteristic of stack-based languages regarding function calls?
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In a sparse switch statement, which technique is often employed?
In a sparse switch statement, which technique is often employed?
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What aspect of control flow does the 'switch' statement primarily handle?
What aspect of control flow does the 'switch' statement primarily handle?
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Which register is used to store the return value of functions in x86-64 architecture?
Which register is used to store the return value of functions in x86-64 architecture?
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Which of the following best describes variable scope in a stack-based language?
Which of the following best describes variable scope in a stack-based language?
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When the stack grows downwards in x86-64 architecture, what happens to the stack pointer during a 'pop' operation?
When the stack grows downwards in x86-64 architecture, what happens to the stack pointer during a 'pop' operation?
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Which technique is commonly used in implementing larger switch statements for efficiency?
Which technique is commonly used in implementing larger switch statements for efficiency?
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Study Notes
Register Usage in x86-64 Linux
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Caller-Saved Registers:
- %rax: Holds return value and can be modified by the procedure.
- %rdi, %rsi, %rdx, %rcx, %r8, %r9: Used to pass arguments, and can be modified by the procedure.
- %r10, %r11: Used as caller-saved temporaries and can be modified by the procedure.
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Callee-Saved Registers:
- %rbx, %r12, %r13, %r14: Callee must save and restore these registers before and after using them.
- %rbp: Acts as a frame pointer:
- The callee must save and restore it.
- Can be used to access local variables.
- %rsp:
- Acts as a stack pointer.
- Restored to its original value upon exiting the procedure.
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Register Usage Roles:
- Caller-Saved: The responsibility of saving and restoring these registers lies with the caller of the function.
- Callee-Saved: The responsibility of saving and restoring these registers lies with the function itself.
Procedures
- A procedure is a named sequence of instructions that perform a specific function.
- A procedure can execute multiple times with different sets of arguments.
- Procedures pass control and data to other parts of the program.
- Procedures manage memory by allocating and deallocating space during execution.
x86-64 Stack
- The x86-64 stack is a region of memory managed using the last-in, first-out (LIFO) principle.
- The stack grows towards lower memory addresses.
- The stack pointer register %rsp points to the top of the stack.
- The pushq instruction decrements the stack pointer and writes the value to the stack.
- The popq instruction reads a value from the stack, increments the stack pointer, and stores the value in a register.
Procedure Data Flow
- The first six arguments are passed to a procedure through registers %rdi, %rsi, %rdx, %rcx, %r8, and %r9.
- The return value is passed through register %rax.
- The stack is used to store arguments beyond the first six and local variables.
Stack-Based Languages
- Stack-based languages, such as C, Pascal, and Java, support recursion and require code to be reentrant.
- Reentrant code allows multiple simultaneous instantiations of a procedure without interfering with each other.
- The stack stores local variables, arguments, and return pointers for each instantiation.
- Stack frames are used to allocate space for a single procedure instantiation.
x86-64/Linux Stack Frame
- The x86-64/Linux stack frame consists of:
- The caller's frame pointer (%rbp)
- The return address
- Arguments passed to the called procedure
- Local variables of the called procedure
- Saved registers
- The stack pointer (%rsp) points to the top of the current stack frame.
- The stack frame is managed using push and pop instructions.
Example: incr
- The incr function takes a pointer to a long integer (p) and a long integer (val) as arguments.
- The function increments the value pointed to by p by val.
- The function returns the original value pointed to by p.
- The function uses registers for all arguments and local variables.
- The value of p is stored in %rdi, val is stored in %rsi, and the return value is stored in %rax.
Call Stack
- The code snippet demonstrates a function call stack. This call stack is used to store information required for subsequent function calls.
- The "call_incr" function calls the "incr" function.
- When a function is called, its return address is added to the call stack.
- In the case of "call_incr", the address "18213" is added to the call stack as it is used as the return address when the "incr" function is executed.
- When a function is called, local variables are allocated in the space allocated to the function on the stack.
- In the case of "call_incr" the value of variable "v1" is allocated space on the stack at address "%rsp+8".
- The function "call_incr" pushes 16 bytes onto the stack to create space for these values.
- The instruction "addq $16, %rsp" pops the values from the stack, removing the temporary space occupied by the variables.
- The instruction "ret" returns control flow to the instruction following the "call" instruction.
- The function "call_incr" takes the return value of "incr" (which is placed in %rax) adds it to the value of "v1" on the stack, then adds the two together.
- The value "v1" is taken from the call stack at the address "%rsp+8".
- The value of variable "v1" is located at address "%rsp+8".
- The function "call_incr" places its return value into the %rax register.
Increment Function ("incr")
- The function "incr" increments the value of the pointer "v1" and stores the new value in the register %rax.
- The "incr" function requires two parameters: a pointer to a variable and a value to add to the variable.
- The "incr" function is called from within the function "call_incr".
- This code illustrates how functions are called and how data is stored in the stack.
- The values passed as arguments to the "incr" function are passed in the %rdi and %rsi registers.
- The value of "v1" is taken from the call stack and addressed using the %rdi register and the value "3000" is stored in the %rsi register.
- The function "incr" first adds the value of the register %rsi (3000) to the value of the memory address stored in %rdi.
- The function "incr" finally returns the incremented value in the %rax register.
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Description
This quiz covers the usage of registers in x86-64 Linux, including caller-saved and callee-saved registers. It discusses the responsibilities of both the caller and the callee related to these registers. Test your knowledge on how these registers are utilized in procedures.
