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:
https://groups.google.com/forum/#!topic/comp.os.linux.embedded/0-SAzCqQKFM And perhaps some of the links below may help you: http://jianggmulab.blogspot.sg/2010_01_01_archive.html http://stackoverflow.com/questions/5647279/why-does-the-module-start-from-address-0xbf000000 http://www.arm.linux.org.uk/developer/memory.txt http://en.wikipedia.org/wiki/High_memory bottomline: keep googling. Q6 and 7 makes no sense to me....sorry. On Mon, Aug 4, 2014 at 11:22 PM, Lucas Tanure <[email protected]> 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! > -- > Lucas Tanure > +55 (19) 988176559 > > > On Sun, Aug 3, 2014 at 8:58 PM, Peter Teoh <[email protected]> > 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 <[email protected]> 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 [email protected]. For more info on Linux MM, > >> see: http://www.linux-mm.org/ . > >> Don't email: <a href=mailto:"[email protected]";> [email protected] </a> > > > > > > > > > > -- > > Regards, > > Peter Teoh > -- Regards, Peter Teoh
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