[Blue forest-free software] - FreeBSD startup-code study notes (reproduced)

FreeBSD Kernel initialization code study notes (1)

Yale Huang

Mailto : goldx@iname.com

FreeBSD Kernel initialization code study notes (1) 1

1. I386/i386/locore.s. 3

2. I386/i386/machdep.c. 4

3. Kern/init_main.c. 5

4. Summary. . . 5

All thanks to Linux, FreeBSD, and GNU utilities, such as Freeware the people who have made contributions.

Recently the FreeBSD Kernel continue studying the initialization code to tidy up a little bit of experience, please correct me.

Due to limitations of the study restricted from beginning for the i386, the other not yet covered platform; The sake of simplicity, there are no details see SMP, KDB have jumped the past, a considerable number of local knowledge is very one-sided. I also saw some of the Linux source, because the Linux source of information to learn more, this knowledge will be very useful for the study of FreeBSD. Taiwan compatriots thinker some six months ago has been written on this part of the document, a great deal of help to these files, see http://cnpa.yzu.edu.tw/~thinker/bsd_kern/, this paper extracts a lot of things in this document.

It is important to point out, from a copy of "FreeBSD startup-code study notes," until now, and I see the initialization process is starting, and the structure and function of many still do not function. I hope it will be sorted out after a rough structure in accordance with the needs and focus of interest in certain parts of a comprehensive look at the source code, I am afraid I have not the power.

I grasped months Global (http://www.tamacom.com/global/) have done a 2.4.16 Linux, FreeBSD 4.3, NetBSD 1.5.2 and Kernel 3.0 OPENBSD the cross reference. But it's good reading source code Eastern also be embedded in emacs, vi Lane use, but HTML to do so if the hard disk on the Linux 2.4.16 too much of a cross reference in the HTML 370MB-- I have them carved R, Three 700MB disc ah.

1. I386/i386/locore.s
Thinker's files, the kernel from locoer.s btext started; Procedures really look like, but I could not find any specific Kernel Makefile is the text of the corresponding things, so there is little doubt. Let us here from the start now.

Locoer.s mainly done several things :

1) initialization page catalog (pde) and the page (ptd), and functions such as paging;

2) Call the i386/i386/machdep.c init386 (), re-instated gdt, ldt and slide, initialization terminal, ISA IRQ, random number generator, tss, virtual 8086 mode (vm86) and the message buffer;

3) Call the mi_startup kern/init_main.c (), "has officially entered the core Kernel" (thinker language).

Say light, it would still take a closer look at the effort, part of this initialization paging function, the need to refer to the files from beginning for the i386. I find from the website of the Inter manual can also find some Chinese from other places, "Pentium II-III, technical architecture and expansion" on the very good.

Thinker that needs some attention, I stole some lazy, there are two important, I think, on the copy (not on the number of firms) :

1) 920-923 Bank. map of the page to a page table directory, the first entry. This is a page table will be "temporary" in the page directory map twice. mainly because the actual implementation of the directive to address the physical address. When I started to enable paging, will be a gray area, so we address the values are still in the physical address map, which is not what we had hoped for the KERNBASE base. Therefore, we do this map. to enable paging, can smooth the implementation of the correct code.

2) 932-935 Bank, PDE will be installed in PDE, it is a recursive approach and make the PDE is on the second floor mapping, turn into the page table. so that the page table mapping the original PDE has become the final destination memory. We can read each page directly through a direct mapping table.

2. I386/i386/machdep.c
Init386 (), a considerable number of tasks :

1), and re-instated gdt ldt. Count re-established the next slide, boot throwing away a part of the whole thing. Gdt use of the provision is the so-called soft_segment_descriptor gdt_segs from ssdtosd () converted into actual descriptor, so as to avoid a lot of spaces to operate trouble.

2) re-instated slide. Init386 () suspended all its worst first 0-255 IDTVEC (rsvd), and then to set up a 0-18 interruption and disruption descriptor 0x80, 0x80 interrupting system call. And the realization of the very system interrupt 0x80 i386/i386/exception.s China.

3) terminal initialization.

4) to set up default IRQ ISA equipment.

5) initialization random number generator.

6) Identification and CPU initialization.

7) failure to prepare TSS.

8) prepared vm86 environment, the actual allocation of space has not only prepared a corresponding table.

9) getmemsize () computer memory size. Thinker described as follows :

1971 trip getmemsize (), i386/i386/machdep.c, 1,419 firms to identify and calculate the memory is available, and reservations msgbuf. Getmemsize will set up a few global variables.

Physmem the page number actually available.

Maxmem physcial memory address to the maximum.

Phys_avail list of available mem block.

Avail_start by pmap_bootstrap ().

Avail_end largest physcial memory address is available. All this is less than the location of the distribution are essential.

10) initialization msg_buf.

11) set up a re-enter (reenter) Kernel with the door. This is the shift in the ldt LSYS5CALLS_SEL (System V Calls?) segement.h said it is "forced by intel BCS." I did not understand.

3. Kern/init_main.c
It was the. Comparing with the init386 (), mi_startup () -- According to the much simpler and sysinit_elem_order system_sub_id sysinit implementation of the sequence of function. Enum:sysinit_sub_id and sysinit_elem_order sys/kernel.h definition of the two, we should pay attention to the SI_SUB_CONSOLE and SI_SUB_SWAP sysinit_sub_id no practical use. Mi_startup () Finally, it should be SI_SUB_RUN_SCHEDULER into sub id for the function. And the sub id SI_SUB_KLD to add a new function in the process of implementing the init function.

Thinker said :

"Mi_startup () linker will use the same section of the initiative to form a continuous block of data characteristics, the initial collection of all sub-system function. This macro function by SYSINIT (). sys/kernel.h, 225 firms reached. mi_startup basis of the information gathered, according to the order of the initial implementation of the sub-system function. sysinit_sub_id definition of the various sub-system implementation of the order. sys/kernel.h, 107 firms, followed by the implementation of mi_startup from small to large. If the same number of initial sub-system function, from sysinit_elem_order, sys/kernel.h, 163 firms. definition of the order of implementation. "

Sysinit the structure is more troublesome, it can be used as a symbol of a particular value end of the array (like string, but elements of a struct). Program structure is scattered when the actual transfer SYSINIT macro structure contains a function pointer, type and priority of struct and insert a section (ELF documents. A.out document processing use. " Stubs "pseudo instructions, gas understand that neither the www.info.gov.hk). This is related to operation and the format of the executable files, the operating system has only a one-off occasion, I think in general with the application or not at all.

4. Summary
Mi_startup () call the init function of the many that I have read the beginning, it is estimated that the structure will be watching Kernel out of the side after I was looking at some notes bars.

Juveniles were not perverts live