Книга: Embedded Linux Primer: A Practical, Real-World Approach
5.1.2. Architecture Objects
5.1.2. Architecture Objects
Following the build sequence further, a number of small modules are compiled. These include several assembly language files (head.o, head-xscale.o, and so on) that perform low-level architecture and processor-specific tasks. Each of these objects is summarized in Table 5-1. Of particular note is the sequence creating the object called piggy.o. First, the Image file (binary kernel image) is compressed using this gzip command:
gzip -f -9 < Image > piggy.gz
This creates a new file called piggy.gz, which is simply a compressed version of the binary kernel Image. You can see this graphically in Figure 5-1. What follows next is rather interesting. An assembly language file called piggy.S is assembled, which contains a reference to the compressed piggy.gz. In essence, the binary kernel image is being piggybacked into a low-level assembly language bootstrap loader.[38] This bootstrap loader initializes the processor and required memory regions, decompresses the binary kernel image, and loads it into the proper place in system memory before passing control to it. Listing 5-2 reproduces .../arch/arm/boot/compressed/piggy.S in its entirety.
Listing 5-2. Assembly File Piggy.S
.section .piggydata,#alloc
.globl input_data
input_data:
.incbin "arch/arm/boot/compressed/piggy.gz"
.globl input_data_end
input_data_end:This small assembly language file is simple yet produces a complexity that is not immediately obvious. The purpose of this file is to cause the compressed, binary kernel image to be emitted by the assembler as an ELF section called .piggydata. It is triggered by the .incbin assembler preprocessor directive, which can be viewed as the assembler's version of a #include file. In summary, the net result of this assembly language file is to contain the compressed binary kernel image as a payload within another imagethe bootstrap loader. Notice the labels input_data and input_data_end. The bootstrap loader uses these to identify the boundaries of the binary payload, the kernel image.
Оглавление книги
- LINQ Architecture
- LINQ to Objects
- Architecture of Silverlight
- Creating and Deleting Device Objects
- 3.2.13. Other Architectures
- 5.2.3. Architecture Setup
- 8.1.2. Device Driver Architecture
- 16.1.1. The Architecture Branch
- 16.4.1. Other Architectures
- 1.4 Microcontroller Architectures
- 2.1 PIC18FXX2 Architecture
- 6.6.1. Objects