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klaudiagrz
reviewed
Jun 22, 2024
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Hi ! I started working on rewording the first article, but then saw you already had a big head start. |
klaudiagrz
reviewed
Jul 15, 2024
| - `rsi` - Used to pass `2nd` argument to a function. | ||
| - `rdx` - Used to pass `3rd` argument to a function. | ||
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| There is more details related to the Linux `x86_64` calling conventions but the description above should be enough for now. Knowing the meaning and the way of use of these registers we can return to the code. What do we need to write a `hello world` program? Usually we just pass a `hello world` string to a library function like [printf](https://en.wikipedia.org/wiki/Printf) or so. But these functions usually goes from a [standard library](https://en.wikipedia.org/wiki/Standard_library) of a programming languages we are using. Assembly does not have a standard library. What to do in this case? Well, we have at least the two following approaches: |
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| There is more details related to the Linux `x86_64` calling conventions but the description above should be enough for now. Knowing the meaning and the way of use of these registers we can return to the code. What do we need to write a `hello world` program? Usually we just pass a `hello world` string to a library function like [printf](https://en.wikipedia.org/wiki/Printf) or so. But these functions usually goes from a [standard library](https://en.wikipedia.org/wiki/Standard_library) of a programming languages we are using. Assembly does not have a standard library. What to do in this case? Well, we have at least the two following approaches: | |
| This knowledge about Linux `x86_64` calling conventions should be enough for now. Knowing the meaning and the usage of the registers, we can return to the code. What do we need to write a `hello world` program? Usually, we just pass a `hello world` string to a library function like [printf](https://en.wikipedia.org/wiki/Printf). But this function usually goes from a [standard library](https://en.wikipedia.org/wiki/Standard_library) of a programming language we use. Assembly does not have a standard library. What to do in this case? Well, we have at least two options: |
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this function usually goes from...
I don't like "goes from", can we replace it with another verb?
| - Link our assembly program with C standard library and use [printf](https://man7.org/linux/man-pages/man3/printf.3.html) or any other function that may help us to write a text to the [standard output](https://en.wikipedia.org/wiki/Standard_streams). | ||
| - Use the operating system API | ||
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| We will go through the second way. Each operating system provides an interface that a user level application may use to interact with the operating system. Usually the functions of this API are called `system calls`. Linux kernel also provides set of system calls to interact with it. The full list of system calls with the respective numbers for the Linux `x86_64` could be found [here](https://github.com/torvalds/linux/blob/master/arch/x86/entry/syscalls/syscall_64.tbl). Looking in this table, we may see: |
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Maybe it's good to mention why we do not explain the first option?
Signed-off-by: Alexander Kuleshov <kuleshovmail@gmail.com>
Signed-off-by: Alexander Kuleshov <kuleshovmail@gmail.com>
Signed-off-by: Alexander Kuleshov <kuleshovmail@gmail.com>
Signed-off-by: Alexander Kuleshov <kuleshovmail@gmail.com>
Signed-off-by: Alexander Kuleshov <kuleshovmail@gmail.com>
Signed-off-by: Alexander Kuleshov <kuleshovmail@gmail.com>
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This PR provides significant rework for the first chapter.