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Merge pull request #210 from pjvandehaar/patch-1

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syscall-1.md: Fix a couple grammar mistakes.
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0xAX 2015-09-17 13:04:00 +06:00
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SysCall/syscall-1.md
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@ -120,7 +120,7 @@ _exit(0) = ?
+++ exited with 0 +++
```
In the first line of the `strace` output, we can see [execve](https://github.com/torvalds/linux/blob/master/arch/x86/entry/syscalls/syscall_64.tbl#L68) system call that executes our program, and the second and third are system calls that we have used in our program: `write` and `exit`. Note that we pass the parameter through the general purpose registers in our example. The order of the registers is not not accidental. The order of the registers is defined by the following agreement - [x86-64 calling conventions](https://en.wikipedia.org/wiki/X86_calling_conventions#x86-64_calling_conventions). This and other agreement for the `x86_64` architecture explained in the special document - [System V Application Binary Interface. PDF](http://www.x86-64.org/documentation/abi.pdf). In a general way, argument(s) of a function are placed either in registers or pushed on the stack. The right order is:
In the first line of the `strace` output, we can see [execve](https://github.com/torvalds/linux/blob/master/arch/x86/entry/syscalls/syscall_64.tbl#L68) system call that executes our program, and the second and third are system calls that we have used in our program: `write` and `exit`. Note that we pass the parameter through the general purpose registers in our example. The order of the registers is not accidental. The order of the registers is defined by the following agreement - [x86-64 calling conventions](https://en.wikipedia.org/wiki/X86_calling_conventions#x86-64_calling_conventions). This and other agreement for the `x86_64` architecture explained in the special document - [System V Application Binary Interface. PDF](http://www.x86-64.org/documentation/abi.pdf). In a general way, argument(s) of a function are placed either in registers or pushed on the stack. The right order is:
* `rdi`;
* `rsi`;
@ -152,7 +152,7 @@ int main(int argc, char **argv)
}
```
There are no `fopen`, `fgets`, `printf` and `fclose` system calls in the Linux kernel, but `open`, `read` `write` and `close` instead. I think you know that these four functions `fopen`, `fgets`, `printf` and `fclose` are just functions that defined in the `C` [standard library](https://en.wikipedia.org/wiki/GNU_C_Library). Actually these functions are wrappers for the system calls. We do not call system calls directly in our code, but using [wrapper](https://en.wikipedia.org/wiki/Wrapper_function) functions from the standard library. The main reason of this is simple: a system call must be performed quickly, very quickly. As a system call must be quick, it must be small. The standard library takes responsibility to perform system calls with the correct set parameters and makes different check before it will call the given system call. Let's compile our program with the following command:
There are no `fopen`, `fgets`, `printf` and `fclose` system calls in the Linux kernel, but `open`, `read` `write` and `close` instead. I think you know that these four functions `fopen`, `fgets`, `printf` and `fclose` are just functions that defined in the `C` [standard library](https://en.wikipedia.org/wiki/GNU_C_Library). Actually these functions are wrappers for the system calls. We do not call system calls directly in our code, but using [wrapper](https://en.wikipedia.org/wiki/Wrapper_function) functions from the standard library. The main reason of this is simple: a system call must be performed quickly, very quickly. As a system call must be quick, it must be small. The standard library takes responsibility to perform system calls with the correct set parameters and makes different checks before it will call the given system call. Let's compile our program with the following command:
```
$ gcc test.c -o test
@ -178,7 +178,7 @@ The `ltrace` util displays a set of userspace calls of a program. The `fopen` fu
write@SYS(1, "Hello World!\n\n", 14) = 14
```
Yes, system calls are ubiquitous. Each program needs to open/write/read file, network connection, allocate memory and many other things that can be provided only by the kernel. The [proc](https://en.wikipedia.org/wiki/Procfs) file system contains special file in a format: `/proc/pid/systemcall` that exposes the system call number and argument registers for the system call currently being executed by the process. For example, pid 1, that is [systemd](https://en.wikipedia.org/wiki/Systemd) for me:
Yes, system calls are ubiquitous. Each program needs to open/write/read file, network connection, allocate memory and many other things that can be provided only by the kernel. The [proc](https://en.wikipedia.org/wiki/Procfs) file system contains special files in a format: `/proc/pid/systemcall` that exposes the system call number and argument registers for the system call currently being executed by the process. For example, pid 1, that is [systemd](https://en.wikipedia.org/wiki/Systemd) for me:
```
$ sudo cat /proc/1/comm