I`m still reading all the resources, but I found a few more.
I didn`t find a few answers yet, but how a module is loaded ?
When you do a insmod the kernel take some pages and load all the module's sections to these pages ?
How this work ? Where I can find more information about memory allocation for a new module.
If I don`t find, I will read the source code for that part, but I try to find a better way to learn. I know that source code is the best and updated, but takes more time too.
And when I do a int inside my module I suppose that my int will be inside that pages that kernel allocated for my new module. Right ??
But if I do this inside kernel code ? It's compiler task do allocate this memory in sections ? How the kernel runs ? Like my module is driven by kernel, but how kernel driven it's self ???
Thanks
On Tue, Aug 5, 2014 at 12:31 AM, Peter Teoh <htmldeveloper@xxxxxxxxx> wrote:
And Q2:Just want to comment that the load address has to be fixed initially, because unlike normal ELF, after loading ELF, there is a relocation tasks done by the linker. In vmlinuz we cannot have relocation, before executing the kernel is the BIOS / uboot / bootloader etc. One possible answer. Others:
And perhaps some of the links below may help you:Q6 and 7 makes no sense to me....sorry.--On Mon, Aug 4, 2014 at 11:22 PM, Lucas Tanure <tanure@xxxxxxxxx> wrote:
Thanks!
A quick look in all of that show me that there a lot of information
about how kernel manage memory.
But, I will find the answer for question 2, 6 and 7 in it ?
Thanks!
On Sun, Aug 3, 2014 at 8:58 PM, Peter Teoh <htmldeveloper@xxxxxxxxx> wrote:
> I like your curiosities and interests in Linux
> kernel.http://virtuallyhyper.com/2013/07/rhcsa-and-rhce-chapter-10-the-kernel/
>
> Instead of answering one by one, I think I will just identify the knowledge
> you are lacking:
>
> Memory management (from both x86/intel and linux kernel perspective).
>
> There are many many resources out there for you in these area, eg:
>
> http://en.wikipedia.org/wiki/Page_table
> http://en.wikipedia.org/wiki/X86-64
>
> (both boring, but just understand it well enough)
>
> http://wiki.osdev.org/Paging (good explanation....understand it very very
> well).
>
> The ultimate classic ebook:
>
> https://www.kernel.org/doc/gorman/pdf/understand.pdf
>
> And this blog site has tons of good info on intel/memory etc:
>
> http://duartes.org/gustavo/blog/post/cpu-rings-privilege-and-protection/
> http://duartes.org/gustavo/blog/post/anatomy-of-a-program-in-memory/
>
> http://virtuallyhyper.com/2013/07/rhcsa-and-rhce-chapter-10-the-kernel/
>
> http://www.cse.psu.edu/~anand/spring01/linux/memory.ppt
>
> One more thing:
>
> "readelf -S -W vmlinux" shows u the sections and the address where the
> different sections are supposed to be loaded in memory. If u replace the
> vmlinux with the kernel module, eg: ip_tables.ko, then it says:
>
> starting at offset 0x328c blah blah....
>
> so the loaded address is with respect to ZERO, but then the actual module
> address is:
>
> sudo cat /proc/modules |grep ip_table
>
> ip_tables 18106 1 iptable_filter, Live 0xf8bf5000
>
> So all the output from your readelf, just add 0xf8bf5000 to it and you will
> get the actual virtual address of that section IN MEMORY.
>
> Just only in memory. In file, the file offset of the section is different.
> And many parts inside the ELF is also different from memory too: you will
> need to add the virtual load address (above) to the offset as specified
> inside the relocation tables (objdump -r), and for each section there is a
> separate relocation table (all independent from another, meaning that the
> different section CAN BE loaded to different parts in memory).
>
> Thanks.
>
>
> On Sun, Aug 3, 2014 at 11:59 PM, Lucas Tanure <tanure@xxxxxxxxx> wrote:
>>
>> Hi,
>>
>> I'm looking for some site, pdf, book etc, that can answer this questions.
>> For now I have :
>>
>> http://unix.stackexchange.com/questions/5124/what-does-the-virtual-kernel-memory-layout-in-dmesg-imply
>>
>>
>> I want to understand a few things about the memory and the execution
>> of Linux kernel.
>> Taking from a X86 and grub I have:
>>
>> 1) Grub loads kernel and root file system in memory, and the vmlinux
>> has the code to decompress it self, right ? linux
>>
>> 2) The address of load kernel is always the same ? And It's at
>> compilation time that is chosen ?
>>
>> 2a) The kernel takes places in 3g-4g memory place, and user space from 0
>> to 3gb.
>> But if the pc has only 256mb of memory ?
>> And when pc has 16gb of memory, the user space will be split in two ?
>>
>> 2b) And if kernel has soo many modules that needs more than 1gb to run ?
>>
>> 2c) How we configure all of that memory configs ? make menuconfig and
>> friends ?
>>
>> 3) The function A will call functon B. B is at 0xGGGGGG in .text
>> section, but kernel was loaded in address 0xJJJJJJJJJJ, how A will
>> find B ?
>>
>> 4) Please consider this:
>> $ readelf -S -W vmlinux
>> There are 37 section headers, starting at offset 0xe05718:
>>
>> Section Headers:
>> [Nr] Name Type Address
>> Off Size ES Flg Lk Inf Al
>> [ 0] NULL
>> 0000000000000000 000000 000000 00 0 0 0
>> [ 1] .text PROGBITS
>> ffffffff81000000 200000 53129a 00 AX 0 0 4096
>> [ 2] .notes NOTE
>> ffffffff8153129c 73129c 0001d8 00 AX 0 0 4
>> [ 3] __ex_table PROGBITS ffffffff81531480
>> 731480 002018 00 A 0 0 8
>> [ 4] .rodata PROGBITS
>> ffffffff81600000 800000 1655ee 00 A 0 0 64
>> [ 5] __bug_table PROGBITS ffffffff817655f0
>> 9655f0 005424 00 A 0 0 1
>> [ 6] .pci_fixup PROGBITS ffffffff8176aa18
>> 96aa18 002f88 00 A 0 0 8
>> [ 7] .tracedata PROGBITS ffffffff8176d9a0
>> 96d9a0 00003c 00 A 0 0 1
>> [ 8] __ksymtab PROGBITS ffffffff8176d9e0
>> 96d9e0 00e710 00 A 0 0 16
>> [ 9] __ksymtab_gpl PROGBITS ffffffff8177c0f0
>> 97c0f0 00a150 00 A 0 0 16
>> [10] __kcrctab PROGBITS ffffffff81786240
>> 986240 007388 00 A 0 0 8
>> [11] __kcrctab_gpl PROGBITS ffffffff8178d5c8
>> 98d5c8 0050a8 00 A 0 0 8
>> [12] __ksymtab_strings PROGBITS ffffffff81792670
>> 992670 01cb42 00 A 0 0 1
>> [13] __init_rodata PROGBITS ffffffff817af1c0
>> 9af1c0 0000e8 00 A 0 0 32
>> [14] __param PROGBITS ffffffff817af2a8
>> 9af2a8 000b00 00 A 0 0 8
>> [15] __modver PROGBITS ffffffff817afda8
>> 9afda8 000258 00 A 0 0 8
>> [16] .data PROGBITS
>> ffffffff81800000 a00000 0e1180 00 WA 0 0 4096
>> [17] .vvar PROGBITS
>> ffffffff818e2000 ae2000 001000 00 WA 0 0 16
>> [18] .data..percpu PROGBITS 0000000000000000
>> c00000 015300 00 WA 0 0 4096
>> [19] .init.text PROGBITS
>> ffffffff818f9000 cf9000 0503ea 00 AX 0 0 16
>> [20] .init.data PROGBITS
>> ffffffff8194a000 d4a000 09e4c8 00 WA 0 0 4096
>> [21] .x86_cpu_dev.init PROGBITS ffffffff819e84c8
>> de84c8 000018 00 A 0 0 8
>> [22] .parainstructions PROGBITS ffffffff819e84e0
>> de84e0 00bd3c 00 A 0 0 8
>> [23] .altinstructions PROGBITS ffffffff819f4220
>> df4220 005f40 00 A 0 0 1
>> [24] .altinstr_replacement PROGBITS ffffffff819fa160
>> dfa160 001a69 00 AX 0 0 1
>> [25] .iommu_table PROGBITS ffffffff819fbbd0
>> dfbbd0 0000f0 00 A 0 0 8
>> [26] .apicdrivers PROGBITS ffffffff819fbcc0
>> dfbcc0 000020 00 WA 0 0 8
>> [27] .exit.text PROGBITS ffffffff819fbce0
>> dfbce0 0009bc 00 AX 0 0 1
>> [28] .smp_locks PROGBITS ffffffff819fd000
>> dfd000 005000 00 A 0 0 4
>> [29] .data_nosave PROGBITS ffffffff81a02000
>> e02000 001000 00 WA 0 0 4
>> [30] .bss NOBITS
>> ffffffff81a03000 e03000 122000 00 WA 0 0 4096
>> [31] .brk NOBITS
>> ffffffff81b25000 e03000 425000 00 WA 0 0 1
>> [32] .comment PROGBITS 0000000000000000
>> e03000 000027 01 MS 0 0 1
>> [33] .debug_frame PROGBITS 0000000000000000
>> e03028 002560 00 0 0 8
>> [34] .shstrtab STRTAB
>> 0000000000000000 e05588 00018a 00 0 0 1
>> [35] .symtab SYMTAB 0000000000000000
>> e06058 1a29f8 18 36 43659 8
>> [36] .strtab STRTAB
>> 0000000000000000 fa8a50 180d92 00 0 0 1
>> Key to Flags:
>> W (write), A (alloc), X (execute), M (merge), S (strings), l (large)
>> I (info), L (link order), G (group), T (TLS), E (exclude), x (unknown)
>> O (extra OS processing required) o (OS specific), p (processor specific)
>>
>> So the vmlinux is loaded in memory like a dd ?
>>
>> 5) In my function A, inside the module that I wrote, a non-initialized
>> variable will take place in non-initialized section that was loaded in
>> memory ?
>> Or my modules has a new sections for it's own use, and my module is
>> loaded my memory like a process, with all his sections?
>> So how another module or kernel code will fin my exported
>> variable/function ?
>>
>>
>> 6) Let's suppose:
>> I have a int variable, with 17 as content, and the address is 0xGGGGGG.
>> If I stop the linux in this time, read my memory at address 0xGGGGGG I
>> will got 17, right ?
>> 0xGGGGGGG will be bigger than 0xc0000000 always, right ?
>>
>>
>> 7) Now take int from question and change for:
>> struct mystruct * foo = (struct mystruct* ) kmalloc(sizeof(struct
>> mystruct));
>>
>> I will be able to read at address 0xGGGGGG the struct that created,
>> and it address will be greater than 0xc0000000, right ?
>> But for this struct, the memory will be allocated for ever, until I
>> free the pointer, right ?
>>
>>
>>
>> Well, this just a start. I really want to understand how kernel is
>> run, loaded etc. Any help is appreciate, answering my questions, links
>> to read, books to read.
>> Actually, I didn't find any book with that kind of information .
>>
>>
>> --
>> Lucas Tanure
>> +55 (19) 988176559
>>
>> --
>> To unsubscribe, send a message with 'unsubscribe linux-mm' in
>> the body to majordomo@xxxxxxxxx. For more info on Linux MM,
>> see: http://www.linux-mm.org/ .
>> Don't email: <a href="" href="mailto:dont@xxxxxxxxx" target="_blank">dont@xxxxxxxxx"> email@xxxxxxxxx </a>
>
>
>
>
> --
> Regards,
> Peter Teoh
Regards,
Peter Teoh
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