Windows interrupts asm

What you understand of assembly for that class of CPU is applicable to all operating systems running on it. When you get to the point that you understand the C calling convention from an assembler point of view the light-bulb moment will happen for you. Second, my personal opinion is that learning the intricacies of DOS is a waste of time.

DOS has been dead for over a decade. The learning curve is nearly identical. From an applications programmer point of view it's actually easier since you don't have to worry about interrupts or IO ports the OS won't let you touch them anyways unless your writing kernel drivers.

Finally, Linux is nothing like DOS. While it's true that both have a command line so does Windows Linux is a multi-user, multi-tasking, operating system suitable for running on your desktop, server, various hardware devices such as Android cell phones or even NASA space probes.

In a nutshell: when starting out pick an OS you're comfortable using and start there. I recommend using C library calls when obtaining input or printing out strings simply because you avoid having to learn OS-specific APIs and the knowledge you gain from that is easily transferable to just about any other OS.

Thank you for the info. If you could, please tell me more about what you are referring to when you mean C Calling convention from an assembler point of view? The sign is changed by inverting all of the bits and adding one. For example, if we are talking about an array, BX contains the address of the beginning of the array, and DI contains the index into the array. It also introduces a new naming convention that must be used for these new registers and can also be used for the old ones except that AH, CH, DH and BH have no equivalents.

In the new convention:. CPU Operation Modes. Real Mode is a holdover from the original Intel The Intel accessed memory using bit addresses. But, as the processor itself was bit, Intel invented an addressing scheme that provided a way of mapping a bit addressing space into bit words.

Today's x86 processors start in the so-called Real Mode, which is an operating mode that mimics the behavior of the , with some very tiny differences, for backwards compatibility. If programming in a modern operating system such as Linux, Windows , you are basically programming in flat bit mode. Any register can be used in addressing, and it is generally more efficient to use a full bit register instead of a bit register part. Additionally, segment registers are generally unused in flat mode, and it is generally a bad idea to touch them.

Using a bit register to address memory, the program can access almost all of the memory in a modern computer. For earlier processors with only bit registers the segmented memory model was used. For larger memory models, these 'segments' can point to different locations.

When writing code, it is very helpful to use some comments explaining what is going on. A comment is a section of regular text that the assembler ignores when turning the assembly code into the machine code. Strictly speaking, assembly has no predefined data types like higher-level programming languages. Any general purpose register can hold any sequence of two or four bytes, whether these bytes represent numbers, letters, or other data.

In the same way, there are no concrete types assigned to blocks of memory; you can assign to them whatever value you like. That said, one can group data in assembly into two categories: integer and floating point.

While you could load a floating point value into a register and treat it like an integer, the results would be unexpected, so it is best to keep them separate. Some assembly instructions behave slightly differently in regards to the sign bit; as such, there is a minor distinction between signed and unsigned integers. Unlike integers where the decimal point is understood to be after all digits, in floating point numbers the decimal point floats anywhere in the sequence of digits.

Originally, floating point was not part of the main processor, requiring the use of emulating software. However, there were floating point coprocessors that allowed operations on this data-type, and starting with the DX, were integrated directly with the CPU.

As such, floating point operations are not necessarily compatible with all processors. If you need to perform this type of arithmetic, you may want to use a software library as a backup code path. Instructions that take 2 operands. Notice how the format of the instruction is different for different assemblers. Instructions that take 3 operands. Operation Suffixes. Some instructions require the use of suffixes to specify the size of the data which will be the subject of the operation, such as:.

An example of the usage with the mov instruction on a bit architecture, GAS syntax:. The mov instruction copies the src operand into the dest operand. The xchg instruction swaps the src operand with the dest operand. It's like doing three move operations: from dest to a temporary another register , then from src to dest, then from the temporary to src , except that no register needs to be reserved for temporary storage.

If one of the operands is a memory address, then the operation has an implicit LOCK prefix, that is, the exchange operation is atomic. This can have a large performance penalty. Almost all programming languages have the ability to change the order in which statements are evaluated, and assembly is no exception. The instruction pointer EIP register contains the address of the next instruction to be executed. To change the flow of control, the programmer must be able to modify the value of EIP.

This is where control flow functions come in. Temp is then discarded. Pushes the address of the next opcode onto the top of the stack, and jumps to the specified location. This is used mostly for subroutines. Loads the next value on the stack into EIP, and then pops the specified number of bytes off the stack. If val is not supplied, the instruction will not pop any values off the stack after returning. The loop instruction decrements ECX and jumps to the address specified by arg unless decrementing ECX caused its value to become zero.

For example:. Using Intel syntax this is equivalent to:. Halts the processor. Execution will be resumed after processing next hardware interrupt, unless IF is cleared. No operation. This instruction doesn't do anything, but wastes an instruction cycle in the processor. This instruction decrements the stack pointer and stores the data specified as the argument into the location pointed to by the stack pointer.

This instruction loads the data stored in the location pointed to by the stack pointer into the argument specified and then increments the stack pointer.

Interrupts are special routines that are defined on a per-system basis. This means that the interrupts on one system might be different from the interrupts on another system. Therefore, it is usually a bad idea to rely heavily on interrupts when you are writing code that needs to be portable.

Hardware interrupts are triggered by hardware devices. Kaustubh Kulkarni. Kaustubh Kulkarni Kaustubh Kulkarni 1 1 1 bronze badge. You just have to vary the calling conventions, but the actual high-level APIs are the same. Also, Windows literally does not have a stable int or syscall ABI for system calls; the call numbers vary by Windows kernel version.

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