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http://lkml.iu.edu/hypermail/linux/kernel/1207.0/03003.html
From: Will Deacon <will.deacon@xxxxxxx> This patch adds VDSO support for 64-bit applications. The VDSO code is currently used for sys_rt_sigreturn() and optimised gettimeofday()
next prev parent reply index Thread overview: 110+ messages / expand[flatnested] mbox.gz Atom feed top 2019-06-21 9:52 [PATCH v7 00/25] Unify vDSOs across more architectures Vincenzo Frascino 2019-06-21 9:52 ` [PATCH v7 01/25] kernel: Standardize vdso_datapage Vincenzo Frascino 2019-06-24 13:56 ` Catalin Marinas 2019-06-21 9:52 ` [PATCH v7 02 ...
https://stackoverflow.com/questions/19938324/what-are-vdso-and-vsyscall
Apr 18, 2016 · The vDSO links are provided via the glibc library. The linker will link in the glibc vDSO functionality, provided that such a routine has an accompanying vDSO version, such as gettimeofday. When your program executes, if your kernel does not have vDSO support, a traditional syscall will be made. Credits and useful links :
https://en.wikipedia.org/wiki/VDSO
vDSO is a memory area allocated in user space which exposes some kernel functionalities. vDSO is dynamically allocated, offers improved safety through memory space randomization, and supports more than 4 system calls. vDSO links are provided via the glibc library. If the kernel does not have vDSO support, a traditional syscall is made.
https://bugzilla.kernel.org/show_bug.cgi?id=198961
This is because there is no support for CLOCK_MONOTONIC_RAW clocks in the VDSO - such calls end up using the vdso_fallback_gettime() method to enter the kernel, perform locking on the gtod structure , and get some adjusted value , when all we want to do for CLOCK_MONOTONIC_RAW is read the Time Stamp Counter (TSC) (issue the rdtsc / rdtscp ...
https://patchwork.kernel.org/patch/7698971/
Some applications such as Checkpoint/Restore In Userspace (CRIU) remap and unmap the VDSO. Add support for this to the AArch64 kernel by copying in the PowerPC code with slight modifications.
http://man7.org/linux/man-pages/man7/vdso.7.html
vdso - overview of the virtual ELF dynamic shared object SYNOPSIS top #include <sys/auxv.h> void *vdso = (uintptr_t) getauxval(AT_SYSINFO_EHDR); DESCRIPTION top The "vDSO" (virtual dynamic shared object) is a small shared library that the kernel automatically maps into the address space of all user-space applications.
https://patchwork.kernel.org/patch/9681273/
Apr 14, 2017 · CRIU restores application mappings on the same place where they were before Checkpoint. That means, that we need to move vDSO and sigpage during restore on exactly the same place where they were before C/R. Make mremap() code update mm->context.{sigpage,vdso} pointers during VMA move.
https://www.ibm.com/support/knowledgecenter/linuxonibm/com.ibm.linux.z.lhdd/lhdd_r_vdsoparm.html
Use the vdso= kernel parameter to control the vdso support for the gettimeofday, clock_getres, and clock_gettime system calls.. The virtual dynamic shared object (vdso) support is a shared library that the kernel maps to all dynamically linked programs. The glibc detects the presence of the vdso and uses the functions that are provided in the library.
https://www.linuxjournal.com/content/creating-vdso-colonels-other-chicken
When your program executes, if your kernel does not have vDSO support, a traditional syscall will be made. This test of vDSO functionality is provided by the code linked from glibc. Of course, you don't want to hack up glibc just so you can have your home-brewed vDSO run.
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