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en:multiasm:paarm:chapter_5_8 [2025/12/04 15:50] – [Bare-Metal program code] eriks.klavinsen:multiasm:paarm:chapter_5_8 [2026/05/27 09:41] (current) – [Bare-Metal program code] ktokarz
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-Build it by calling "''as -o hello.o hello.s''" and then "''ld -o hello hello.o''" commands in the Linux OS command line. After that it can be executed by the "''./hello''" command. During program execution time, the “''Text Message!''” should be shown in the terminal. This example uses the Linux OS system calls.+Build it by calling "''as -o hello.o hello.s''" and then "''ld -o hello hello.o''" commands in the Linux-based OS command line. After that, it can be executed by the "''./hello''" command. During program execution time, the “''Text Message!''” should be shown in the terminal. This example uses the Linux system calls.
  
 ===== System calls  ===== ===== System calls  =====
  
-The way Raspberry Pi OS calls created code depends on how it is built and how it runs, because this can be done at several different levels. The code can be written and executed as a user-space program on some OS, such as Linux. It is the most common and at the same time the easiest way to create and execute assembly code. Raspberry Pi Os will build and create assembly code into an ELF executable.\\+The way Raspberry Pi OS calls created code depends on how it is built and how it runs, because this can be done at several different levels. The code can be written and executed as a user-space program on some OS, such as Linux-based. It is the most common and at the same time the easiest way to create and execute assembly code. Raspberry Pi Os will build and create assembly code into an ELF executable.\\
 Commands “''as -o program.o program.s''” and “''ld -o program program.o''” create a Linux executable file. This file follows the ELF format (Executable and Linkable Format). After that, the developed program can be executed as an ordinary Linux program (i.e. ‘./program’). At this moment, the shell (bash) calls the Linux kernel using the ''execve()'' system call. The Linux kernel reads the ELF header of the newly created program and loads the code and data into memory. The kernel also arranges the stack and, if arguments are passed to the program, prepares the registers and their initial values. And the last thing for the kernel is to set the program counter register to the ''_start'' symbol in the program, the memory address where the Linux kernel copied the program code it created. At this point, the created program code begins executing - the designed program is being called like an ordinary function - we can pass the arguments and receive the data. Commands “''as -o program.o program.s''” and “''ld -o program program.o''” create a Linux executable file. This file follows the ELF format (Executable and Linkable Format). After that, the developed program can be executed as an ordinary Linux program (i.e. ‘./program’). At this moment, the shell (bash) calls the Linux kernel using the ''execve()'' system call. The Linux kernel reads the ELF header of the newly created program and loads the code and data into memory. The kernel also arranges the stack and, if arguments are passed to the program, prepares the registers and their initial values. And the last thing for the kernel is to set the program counter register to the ''_start'' symbol in the program, the memory address where the Linux kernel copied the program code it created. At this point, the created program code begins executing - the designed program is being called like an ordinary function - we can pass the arguments and receive the data.
  
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 After that, the code will continue to execute until the power is switched off, the processor is RESET, or an unexpected exception occurs. Here, the code is responsible for everything, including setting up the stack pointer, enabling caches, handling interrupts, and working with devices directly at hardware addresses. This requires reviewing all hardware-related documentation. But these programs tend to be much faster and more robust than OS related programs. This is a typical way to design programs such as device firmware, RTOS, or bootloader. After that, the code will continue to execute until the power is switched off, the processor is RESET, or an unexpected exception occurs. Here, the code is responsible for everything, including setting up the stack pointer, enabling caches, handling interrupts, and working with devices directly at hardware addresses. This requires reviewing all hardware-related documentation. But these programs tend to be much faster and more robust than OS related programs. This is a typical way to design programs such as device firmware, RTOS, or bootloader.
  
-The same code can be adjusted to work as a kernel module or a driver. In such a case, the code will require much more editing and investigation into OS-related documentation. The kernel must know how often this program should execute, and it may also need to work with mutexes. This is better implemented in C, as it involves multiple runtime libraries from the Linux OS.+The same code can be adjusted to work as a kernel module or a driver. In such a case, the code will require much more editing and investigation into OS-related documentation. The kernel must know how often this program should execute, and it may also need to work with mutexes. This is better implemented in C, as it involves multiple runtime libraries from the Linux-based OS.
  
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