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Diffstat (limited to 'open_issues/vdso.mdwn')
| -rw-r--r-- | open_issues/vdso.mdwn | 48 |
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diff --git a/open_issues/vdso.mdwn b/open_issues/vdso.mdwn new file mode 100644 index 00000000..2b2d2805 --- /dev/null +++ b/open_issues/vdso.mdwn @@ -0,0 +1,48 @@ +[[!meta copyright="Copyright © 2013 Free Software Foundation, Inc."]] + +[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable +id="license" text="Permission is granted to copy, distribute and/or modify this +document under the terms of the GNU Free Documentation License, Version 1.2 or +any later version published by the Free Software Foundation; with no Invariant +Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license +is included in the section entitled [[GNU Free Documentation +License|/fdl]]."]]"""]] + +[[!tag open_issue_glibc open_issue_gnumach open_issue_hurd]] + +Evaluate whether or not usage of vDSOs (virtual dynamically linked shared +objects; [[!wikipedia vDSO]]) can be useful in a GNU Hurd system. + +Explanation and example for the Linux kernel: [Creating a vDSO: the Colonel's +Other +Chicken](http://www.linuxjournal.com/content/creating-vdso-colonels-other-chicken), +Matt Davis, 2012-02-06. The *Resources* given are also worth reading. +Basically, this is useful for exporting data from the kernel (generally, or +given a process context ([[Unix]]), or task/thread context, and so on). + +On a GNU Hurd system, parts of the data that makes up a process context doesn't +actually live inside the kernel, but instead is directly held in glibc. For +example `sysdeps/mach/hurd/getpid.c:__getpid` does a mere `return _hurd_pid`. +For this reason, vDSOs might not be as useful on GNU Hurd as they are with the +Linux kernel. Or, put another way, as GNU Hurd system doesn't have many +[[system_call]]s, also there aren't many that could be replaced. + +Generally only *real* [[system_call]]s should be candidates for implementation +with vDSO code, because otherwise that'd break the ([[RPC]]) system's inherent +[[/virtualization]] capabilities. + +Having vDSO code might be useful for: + + * `mach_*_self`: `mach_host_self`, `mach_task_self`, `mach_thread_self`? + + * [[mapped-time_interface|master/microkernel/mach/gnumach/interface/device/time]] + + Every application can then use that via the regular + `gettimeofday`/`clock_gettime` and similar calls instead of using the + special [[hurd/libshouldbeinlibc]]'s `<maptime.h>` interface. + + Can implement [[`clock_gettime` stuff|clock_gettime]] more easily that way, + for example for nanosecond precision? + + Now, the [[mapped-time_interface]] is virtualizable -- the question is + whether there is a way so that we can make a compromise here? |