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Compiling enough of the kernel to get symbols for EXTMODs, but no more
by David Wuertele July 27, 2011

July 27, 2011

I have a problem where I seem to need to compile the kernel twice, and I am looking for a way to not have to repeat any compilation steps. I have an embedded system kernel into which I'm bundling an initramfs. That initramfs contains some modules that must be compiled external to the kernel (due to my vendor's funky build system). Before I do that I must compile the kernel, so that the external module compilation can insert the kernel symbols into mymodule.mod.c. But after the module is compiled, I must install it into the initramfs and recompile the kernel. I want the kernel to contain a bundled initramfs to simplify distribution. But I would rather not compile the kernel twice. I'm wondering if there is a target in the kernel makefile that will allow me to compile just enough of the kernel such that when I compile the external module it gets the proper symbols. I tried something like this: make -C $(LINUX) prepare scripts make -C $(LINUX) M=$(PATH_TO_MY_MODULE) modules cp $(PATH_TO_MY_MODULE)/mymodule.ko $(PATH_TO_MY_ROOTFS_STAGING)/lib make -C $(LINUX) CONFIG_INITRAMFS_SOURCE=$(PATH_TO_MY_ROOTFS_STAGING) but after booting that kernel, mymodule.ko would not load because it was missing the proper symbols. When I look at the file $(PATH_TO_MY_MODULE)/mymodule.mod.c, the block assigned to section("__versions") is empty. Apparently I need to compile more than just "prepare scripts" in my first step. I find that this works: make -C $(LINUX) CONFIG_INITRAMFS_SOURCE=$(PATH_TO_MY_ROOTFS_STAGING) make -C $(LINUX) M=$(PATH_TO_MY_MODULE) modules cp $(PATH_TO_MY_MODULE)/mymodule.ko $(PATH_TO_MY_ROOTFS_STAGING)/lib make -C $(LINUX) CONFIG_INITRAMFS_SOURCE=$(PATH_TO_MY_ROOTFS_STAGING) But that has some redundancy that I want to avoid. Is there a build target that I could use for my first step that goes far enough in building the kernel, but doesn't actually do the step of marshalling the initramfs and linking it into the kernel? Thanks, Dave

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Bond, round robin mis-configuration.
by Eduard Sinelnikov July 27, 2011

July 27, 2011

Hi, In the kernel 2.6.39.3 ( /drivers/net/bond/bond_main.c). In the function ‘bond_xmit_roundrobin’ The code check if the bond is active via ‘bond_is_active_slave(slave)’ Function call. Which actually checks if the slave is backup or active What is the meaning of slave being backup in round robin mode? Correct me if I wrong but in round robin every slave should send a packet, regardless of being active or backup. Thank you, Eduard

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Regarding perf top utility in linux
by ankur dwivedi July 27, 2011

July 27, 2011

Hi, The perf top utility on linux displays the samples and the pcnt values for each function. I looked into the code of perf top in builtin-top.c in the linux kernel. What i have understood is perf top does not display the actual hardware performance counters value in the samples. It just maintains a software counter for each event for each function entry in the symbol table and increments the counter when that function causes a particular event. Is my understanding correct? -- Thanks Ankur

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about create_mapping function
by sandeep kumar July 27, 2011

July 27, 2011

Hi, I m trying to understand how different io memory is mapped to the CPU. While analysing that i was struck at create_mapping function. i have several questions like, 1) Why map_desc.virtual is filled with physical address of the io device. 2) What is a section and why it is needed? 3) I am not understanding "alloc_init_section(pgd, addr, next, phys, type);" what it does? -- With regards, Sandeep Kumar Anantapalli,

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when early_param("string", function_name) will be called?
by sandeep kumar July 26, 2011

July 26, 2011

Hi all, In kernel code at lot of places i came across "early_param("string", function_name)" Eg: early_param("vmalloc", early_vmalloc); in arch/arm/mm/mmu.c when this function will be called? and what is the significance of the string "vmalloc" there? Thank you.. -- With regards, Sandeep Kumar Anantapalli,

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failed to do make menuconfig
by Prashant Shah July 26, 2011

July 26, 2011

Hi, In the latest staging tree I cant do "make menuconfig" or even "make config" prashant@mint11 ~/linux-2.6 $ make menuconfig HOSTCC scripts/kconfig/mconf.o HOSTCC scripts/kconfig/zconf.tab.o In file included from scripts/kconfig/zconf.tab.c:90:0: scripts/kconfig/lkc.h:27:22: fatal error: lkc_defs.h: No such file or directory compilation terminated. make[1]: *** [scripts/kconfig/zconf.tab.o] Error 1 make: *** [menuconfig] Error 2 Even against the latest linux 3.0.0 tree I get this HOSTCC scripts/kconfig/zconf.tab.o In file included from scripts/kconfig/zconf.tab.c:90:0: scripts/kconfig/lkc.h:27:22: fatal error: lkc_defs.h: No such file or directory compilation terminated. make[1]: *** [scripts/kconfig/zconf.tab.o] Error 1 make: *** [menuconfig] Error 2 I am using latest version of Mint Linux

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Interesting case while taking Ramdump of Linux kernel based device
by sandeep kumar July 26, 2011

July 26, 2011

Hi all, In Android target mobiles there is a facility called "Ramdump", where the entire Ram image is copied to a file as the kernel goes to panic. Ramdump is implemented like this 1) As the panic() function is called target will be reset. 2) Bootloader boots up in specific mode, where it enables the USB driver in uploading mode. 3) Through USB entire RAM content is copied to a file in the host computer. 4) This file is parsed through different tools and we can get the logs info wat exactly happened just before kernel panic happend. Now here is the interesting part, While the mobile's RAM image is being uploaded to host computer, our bootloader is still running in the mobile's RAM. How can it copy its own running region. This triggered me the following questions, 1) When bootloader runs, will it run in a specific reserved region of RAM or it takes entire RAM? 2) When it hands over the control to kernel, will it relinquish the entire RAM or certain part of RAM is reserved for it? 3) Does kernel use the entire RAM while running? 4) When the kernel is running, is ther any chance that, control again be taken back to bootloader?(coz i saw in bootloader code kernel is being called, after that code also some code is there,some printks and error handling stuff) Pls help me out here.. -- With regards, Sandeep Kumar Anantapalli,

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no files can be opened in a C program
by Venkateswarlu P July 26, 2011

July 26, 2011

What is the Max no of files that can be opened simultaneously within a Single C program. i want this information for kenel compilation

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Query regarding kernel memory
by Vaibhav Jain July 26, 2011

July 26, 2011

Hi, I read a few articles on linux virtual memory management such as this one : http://lwn.net/Articles/75174/ which say that earlier linux kernel could only use memory slightly below 1 GB. They have given the reason for it but I am unable to understand.They further describe the use of High memory and low memory. Could anybody please explain the reason for kernel not being able to use the 1 GB completely? Also please provide references for high memory and low memory. Thanks Vaibhav Jain

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T.XYZ symbols
by Andreas Platschek July 25, 2011

July 25, 2011

Hi! I got a bunch of Call-Traces like this: 8312.002483] Call Trace: [ 8312.002502] [<c101eaff>] __might_sleep+0xd7/0xde [ 8312.002517] [<c1053478>] T.396+0x17/0x21 [ 8312.002531] [<c129edf3>] rt_spin_lock+0xb/0x28 [ 8312.002578] [<f966cf92>] b43_interrupt_handler+0x1a/0x34 [b43] [ 8312.002594] [<c106df92>] handle_irq_event_percpu+0x82/0x1bd [ 8312.002609] [<c106e0f9>] handle_irq_event+0x2c/0x43 <snip> and was wondering about the second symbol T.396. greping over the kernel tree only finds it in binaries and the System.map. I have been searching around without a real plan. any hints on that? thx! andi

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