Assembly Language Programming

There is no difference between the SAL and SHL instructions. They both perform the same operations.

The SAR instruction is used for signed data and performs an arithmetic right shift.

The SHR instruction is used for unsigned data and performs a logical right shift.

<p>The purpose of using C structs in assembly code is to access and manipulate structured data in a more organized and efficient manner.</p> Signup and view all the answers

<p>To access the value of 't.x' in assembly code, you would use the instruction 'movl (%edx), %eax', where 'edx' is the pointer to the struct and 'eax' is the register to store the value.</p> Signup and view all the answers

<p>The left shift instructions (SAL/SHL) are used to shift the bits in a byte, word, or long word by a variable number of positions, and are commonly used to implement the C language operators &gt;.</p> Signup and view all the answers

<p>SAL and SHL instructions perform the same operations, which is left shifting the bits. The only difference is that SAL is used for signed data (arithmetic left shift) and SHL is used for unsigned data (logical left shift).</p> Signup and view all the answers

<p>The SAR instruction is used for right shifting signed data (arithmetic right shift). It preserves the sign bit and shifts the remaining bits to the right.</p> Signup and view all the answers

<p>The SHR instruction is used for right shifting unsigned data (logical right shift). It shifts all the bits to the right, including the sign bit, which is set to 0.</p> Signup and view all the answers

<p>The purpose of using C structs in assembly code is to access and manipulate structured data in a high-level language like C, while still being able to optimize and control the low-level details of the assembly code.</p> Signup and view all the answers

<p>To access the value of 't.y' in assembly code, you would use the appropriate memory address offset of 't.y' relative to the base address of the structure.</p> Signup and view all the answers

<p>The left shift instructions (SAL / SHL) are used to shift the bits in a byte, word, or long word to the left by a variable number of positions, implementing the left shift operator in the C language.</p> Signup and view all the answers

<p>The purpose of the CMPB instruction in Gas code is to set/reset the flags based on the comparison between two values.</p> Signup and view all the answers

<p>The condition for the jl jump instruction in signed comparisons is 'less than'.</p> Signup and view all the answers

<p>The carry flag indicates underflow in unsigned comparisons.</p> Signup and view all the answers

<p>The purpose of the loop instruction is to decrement, test, and jump based on the value of the %ecx register.</p> Signup and view all the answers

<p>Jump instructions are used to implement branching and looping in assembly language, similar to 'if-else' and 'for' statements in higher-level languages.</p> Signup and view all the answers

<p>A jump instruction transfers control to a different part of the program without pushing a return address onto the stack, while a 'call' instruction transfers control to a subroutine and pushes a return address onto the stack.</p> Signup and view all the answers

<p>The flowchart is a design technique commonly used in assembly language programming to represent the flow of control and logic in a program, with circles representing labels and arrows representing 'go-to' instructions.</p> Signup and view all the answers

<p>The purpose of a conditional jump instruction in assembly code is to modify the flow of control based on the state of specific flags in the %eflags register. If the condition specified by the flags is true, the instruction will load a new value into the %eip register, otherwise the instruction will let the %eip be incremented to the next sequential instruction.</p> Signup and view all the answers

<p>The flags that can be set by arithmetic or logical instructions in assembly code are the Carry Flag, Zero Flag, Sign Flag, Parity Flag, Overflow Flag, and Auxiliary Carry Flag.</p> Signup and view all the answers

<p>The purpose of the Carry Flag in assembly code is to indicate whether an addition or subtraction operation resulted in a carry out or borrow into the most significant bits added or subtracted.</p> Signup and view all the answers

<p>The purpose of the Overflow Flag in assembly code is to indicate whether the sum of two numbers with the sign bits off yields a result number with the sign bit on, or whether the sum of two numbers with the sign bits on yields a result number with the sign bit off.</p> Signup and view all the answers

<p>.text for the code section and .data for the data section.</p> Signup and view all the answers

<p>Indirect addressing allows the use of a register as the address of the memory location to access in an instruction.</p> Signup and view all the answers

<p>The Intel instruction set does not support instructions to move a value from memory to memory. It always requires a register as an intermediate location for the value being moved.</p> Signup and view all the answers

<p>The cpuid function retrieves the CPU ID value and stores it in a string buffer.</p> Signup and view all the answers

<p>Easier to read and understand source code; Requires fewer lines of code for same function; Does not require knowledge of the hardware.</p> Signup and view all the answers

<p>It is a good way to learn how a processor works; It is possible to improve performance in time-critical sections of code; It is necessary in writing a new operating system or in porting an existing system to a new machine.</p> Signup and view all the answers

<p>To let C do most of the work and integrate with assembly code where needed; To make gas routines callable from C by using C compiler conventions for function calls and preserving registers that C compiler expects saved.</p> Signup and view all the answers

<p>Label, Mnemonic, Operand(s), Comment.</p> Signup and view all the answers

<p>Self-modifying code refers to the practice of a program modifying its own instructions during runtime. However, self-modifying code may not work in situations where the code is physically located in PROM/ROM or if there is an operating system like UNIX/Linux that protects the code space from being modified.</p> Signup and view all the answers

<p>Here is an example of self-modifying code in C:</p> <p>int main(int argc, char **args) { // array to hold the machine code bytes of the function static char function;</p> <pre><code>// put code instructions byte by byte into the function array function[0] = 0xb8; // move address of the string to %eax. function[1] = 0xc3; // and return. // execute the function whose address is the array printf(&quot;%s\n&quot;, (* (char * (*)()) function) ()); return 0; </code></pre> <p>}</p> Signup and view all the answers

<p>The CMPB instruction in Gas code is used to compare two bytes or characters. It subtracts the second operand from the first operand and sets the flags accordingly. The result of the subtraction is not stored, but the flags are updated based on the result.</p> Signup and view all the answers