Re: Why exported const value modified by another driver not updated in original driver
On Tue, Sep 4, 2012 at 5:55 PM, Dan Carpenter dan.carpen...@oracle.com wrote: On Tue, Sep 04, 2012 at 03:58:20PM +0530, Manavendra Nath Manav wrote: Is the above a genuine kernel bug, or i am missing something out here. Pls help. When you declare something as const then the compiler assumes it really is const and uses a literal instead of reading from memory. I'm surprised the compiler doesn't print a warning message. It has to do with compilers, nothing to do with kernels. regards, dan carpenter Thanks All, I understood the problem and current gcc behaviour after looking at output of objdump of driver.ko file when the variable is declared as const and in second case as const volatile. The compiler optimises by directly passing the value in first case and the address of variable in second case. Thanks for all the help and clarification. push $0x7b // 123 in decimal push $0x0 -- Manavendra Nath Manav ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Why __force sparse annotation needed in copy_from_user() to vmalloc'ed area
Hello, In the course of reviewing a new framebuffer driver [1], I discovered the following bit of code: + dst = (void __force *) (info-screen_base + p); + + if (copy_from_user(dst, buf, count)) + err = -EFAULT; Where info-screen_base is a vmalloc'ed memory area. Many other framebuffer drivers have used this __force sparse annotation: see [2] or [3] for example. I am confused as to why sparse requires the __force annotation for what seems to be a regular user to kernel copy. The __force annotation is typically not needed for user to kernel copy when the destination kernel buffer has been kmalloc'ed. Why does sparse handles vmalloc'ed buffer differently, and gives a warning in this case? Thanks, Thomas [1] http://marc.info/?l=linux-fbdevm=134683775709128w=2 [2] http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=28cdf76bf0bce757428f84161e3aa510028d47b4 [3] http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=d2e8d369cd92a8bb856ff530fa1e4c03b0e0ff55 -- Thomas Petazzoni, Free Electrons Kernel, drivers, real-time and embedded Linux development, consulting, training and support. http://free-electrons.com ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
module loading issue module_layout
Hi As the kernel source not available for running kernel code of an Andodiod tablet, I could not able to match module_layout address of my loadable module with the android tablet running kernel even the kernel versions are same. Is there a way to generate build environment in such a situation as the manufacture source is bit deviated from source he has posted on the net. Regards ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: module loading issue module_layout
On Wed, Sep 5, 2012 at 7:04 PM, Kshemendra KP kshemen...@suphalaam.com wrote: Is there a way to generate build environment in such a situation as the manufacture source is bit deviated from source he has posted on the net. a friend of mine said, you should just use Android SDK. But I am not sure whether that also applies to kernel space. -- regards, Mulyadi Santosa Freelance Linux trainer and consultant blog: the-hydra.blogspot.com training: mulyaditraining.blogspot.com ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Places where the kernel modifies itself (.text) during runtime
Hello, I am trying to determine all the ways/methods in which the kernel will modify its own .text section after the machine has booted. I am working with the latest Fedora kernel (3.5.2-3.fc17.x86_64). So far I have identified: 1) smp_locks 2) .alt_instructions - although from writing a script to parse the alt_instr structures, it seems these may not affect .text, any clarification on this would be greatly appreciated. 3) dynamic ftracing (related to mcount) 4) I also see where the paravirt instructions (PVOP_CALL4) seems to compile as absolute call instructions, but then become relative calls at runtime. I figured this one out this by diffing the disassembly of xen_cpuid_base in both memory and from the vmlinux after noticing they were not the same: # diff xen_cpuid_base-memory xen_cpuid_base-disk 20,21c20 003C E8A2E5A3FFcall dword 0xffa3e5e3 0041 6690 xchg ax,ax --- 003C FF142580DCC181call qword [0x81c1dc80] and the 0x81c1dc80 instruction relates to the cpuid function which ends up in paravirt code. Any clarifications or links to docs on this changing of the calls in the paravirt subsystem would be helpful. I also would like to find out if the kernel changes itself in any other way besides those that I have listed. Thanks, Andrew ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: Places where the kernel modifies itself (.text) during runtime
Hi Andrew... On Thu, Sep 6, 2012 at 2:56 AM, Andrew Case atc...@gmail.com wrote: So far I have identified: 1) smp_locks 2) .alt_instructions - although from writing a script to parse the alt_instr structures, it seems these may not affect .text, any clarification on this would be greatly appreciated. 3) dynamic ftracing (related to mcount) 4) I also see where the paravirt instructions (PVOP_CALL4) seems to compile as absolute call instructions, but then become relative calls at runtime. maybe also kprobe and dynamic printk -- regards, Mulyadi Santosa Freelance Linux trainer and consultant blog: the-hydra.blogspot.com training: mulyaditraining.blogspot.com ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
