September 2016 - Darwin-kernel

Re: Retreiving command line of process
by Richard Hamilton 12 Sep '16

12 Sep '16

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Re: Retreiving command line of process
by Quinn "The Eskimo!" 12 Sep '16

12 Sep '16

On 12 Sep 2016, at 04:44, Charu Tiwari <cctiwari(a)gmail.com> wrote: > Is there any way we can get "full path" (command line) of process in 'kext' (given a 'pid' is available). Not directly. A common approach here is to bounce the work out to user space. And once you do that you can user other APIs, like that code signing API, that are generally better for identifying code anyway. Share and Enjoy -- Quinn "The Eskimo!" <http://www.apple.com/developer/> Apple Developer Relations, Developer Technical Support, Core OS/Hardware _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists… This email sent to site_archiver(a)lists.apple.com

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Retreiving command line of process
by Charu Tiwari 12 Sep '16

12 Sep '16

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Re: Holding a spinlock
by Stan Sieler 07 Sep '16

07 Sep '16

Re: > faster than pthread mutexes. I am writing a (user code) OSSpinlock equivalent > that uses a 1-byte (or 1-bit) flag rather than a 4-byte spinlock. > And want to make it as fast as possible. I'll echo Shantonu's (implicit) advice: whenever possible, use a locking mechanism the vendor (Apple in this case) provides. Why? 1. Users make mistakes, introducing bugs. If Apple's locking mechanism has a bug, it gets fixed fast and everyone using it benefits automatically. If your code has a bug, it takes longer to find/fix, and not all users get the fix as quickly as you'd like. 2. The performance gain is generally far, **far**, outweighed by the development cost. I.e., let's say you save a millisecond a day. If it takes 10 hours to code/debug/test/document your locking mechanism, you'll see the savings after about 78 thousand years. If you save a second a day, you'll see the savings after about one century. If you save a minute a day (which would be utterly astounding), you'll see the savings after about 2 years. I gave this same advice to HP-UX developers (and the HP-UX kernel lab) several decades ago, and it's still relevant :) The HP-UX kernel lab ignored it, and told developers the "best way" to write a user-level spinlock. Six months later, they were telling developers "oops", their published method was wrong :) Also, HP-UX developers who used a kernel supported mechanism found that it worked quite well when HP-UX moved from PA-RISC to Itanium, a move which made the assembly-level roll-your-own people rewrite their PA-RISC code. Does OS X have a good kernel supported locking mechanism that users can use? I don't know. It should. If it doesn't, lobby for one ... because that's the right way to improve the world for everyone :) Stan _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists… This email sent to site_archiver(a)lists.apple.com

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Re: Holding a spinlock
by Shantonu Sen 06 Sep '16

06 Sep '16

None of the constraints of kernel synchronization apply to user mode synchronization. Hand-rolled spin locks can be faster and have reduced storage than pthread mutexes, however they frequently also have either reduced functionality (like priority propagation, owner detection, correctness assertions, recursive acquisition) and worst-case performance (unfairness, CPU usage under contention, inversions under system load). Unless you can characterize these all, you likely should not be writing your own locks except as an experiment. Shantonu > On Sep 6, 2016, at 2:30 PM, Adriaan van Os <gpc(a)microbizz.nl> wrote: > > Shantonu Sen wrote: >> What are you actually trying to do? >> If you want to acquire a lock and then execute code in the critical section which might block, you should use a mutex. On x86, kernel mutexes have an adaptive spin before they block on contention, so in practice critical sections of a few instructions should not cause other contending threads to enter the scheduler. > > I am just curious to know all the implementation details. I did some tests (in user code) with various locking/atomic methods and noticed that OSSpinlocks are extremely fast, a zillion times faster than pthread mutexes. I am writing a (user code) OSSpinlock equivalent that uses a 1-byte (or 1-bit) flag rather than a 4-byte spinlock. And want to make it as fast as possible. > > Regards, > > Adriaan van Os > _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists… This email sent to site_archiver(a)lists.apple.com

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Re: Holding a spinlock
by Adriaan van Os 06 Sep '16

06 Sep '16

Shantonu Sen wrote: What are you actually trying to do? If you want to acquire a lock and then execute code in the critical section which might block, you should use a mutex. On x86, kernel mutexes have an adaptive spin before they block on contention, so in practice critical sections of a few instructions should not cause other contending threads to enter the scheduler. Regards, Adriaan van Os _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists… This email sent to site_archiver(a)lists.apple.com I am just curious to know all the implementation details. I did some tests (in user code) with various locking/atomic methods and noticed that OSSpinlocks are extremely fast, a zillion times faster than pthread mutexes. I am writing a (user code) OSSpinlock equivalent that uses a 1-byte (or 1-bit) flag rather than a 4-byte spinlock. And want to make it as fast as possible.

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Re: Holding a spinlock
by Shantonu Sen 06 Sep '16

06 Sep '16

What are you actually trying to do? If you want to acquire a lock and then execute code in the critical section which might block, you should use a mutex. On x86, kernel mutexes have an adaptive spin before they block on contention, so in practice critical sections of a few instructions should not cause other contending threads to enter the scheduler. Shantonu > On Sep 3, 2016, at 5:44 PM, John Kraft <jfk(a)uaudio.com> wrote: > > > We use IOSimpleLocks from the IOKit for this. These are just wrappers around the lck primitives, though. > > > ________________________________________ > From: darwin-kernel-bounces+jfk=uaudio.com(a)lists.apple.com <darwin-kernel-bounces+jfk=uaudio.com(a)lists.apple.com> on behalf of Adriaan van Os <gpc(a)microbizz.nl> > Sent: Saturday, September 3, 2016 2:13 PM > To: darwin-kernel(a)lists.apple.com > Subject: Holding a spinlock > > The Kernel Programming Guide in the Synchronization Primitives chapter says the following in the > Locks section, Spinlocks subsection > > Note that a thread may not block while holding a spinlock, because that could cause deadlock. > Further, preemption is disabled on a given processor while a spinlock is held. > > I assume the code will be something like (in Linux <http://www.makelinux.net/books/lkd2/ch06lev1sec7>) > > local_irq_disable(); > spin .... > local_irq_enable(); > > However, I haven't been able to locate the code that does this or similar, at least not in > osfmk/kern/locks.c. What is the recommended practice on Mac OS X ? I mean, apart from using the > lck_ functions, who are not practical to use in my case. > _______________________________________________ > Do not post admin requests to the list. They will be ignored. > Darwin-kernel mailing list (Darwin-kernel(a)lists.apple.com) > Help/Unsubscribe/Update your Subscription: > https://lists.apple.com/mailman/options/darwin-kernel/ssen%40apple.com > > This email sent to ssen(a)apple.com _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists… This email sent to site_archiver(a)lists.apple.com

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Re: Holding a spinlock
by John Kraft 04 Sep '16

04 Sep '16

We use IOSimpleLocks from the IOKit for this. These are just wrappers around the lck primitives, though. ________________________________________ From: darwin-kernel-bounces+jfk=uaudio.com(a)lists.apple.com <darwin-kernel-bounces+jfk=uaudio.com(a)lists.apple.com> on behalf of Adriaan van Os <gpc(a)microbizz.nl> Sent: Saturday, September 3, 2016 2:13 PM To: darwin-kernel(a)lists.apple.com Subject: Holding a spinlock The Kernel Programming Guide in the Synchronization Primitives chapter says the following in the Locks section, Spinlocks subsection Note that a thread may not block while holding a spinlock, because that could cause deadlock. Further, preemption is disabled on a given processor while a spinlock is held. I assume the code will be something like (in Linux <http://www.makelinux.net/books/lkd2/ch06lev1sec7>) local_irq_disable(); spin .... local_irq_enable(); However, I haven't been able to locate the code that does this or similar, at least not in osfmk/kern/locks.c. What is the recommended practice on Mac OS X ? I mean, apart from using the lck_ functions, who are not practical to use in my case. _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists… This email sent to site_archiver(a)lists.apple.com

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Holding a spinlock
by Adriaan van Os 03 Sep '16

03 Sep '16

I assume the code will be something like (in Linux <http://www.makelinux.net/books/lkd2/ch06lev1sec7>) local_irq_disable(); spin .... local_irq_enable(); Regards, Adriaan van Os _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists… This email sent to site_archiver(a)lists.apple.com The Kernel Programming Guide in the Synchronization Primitives chapter says the following in the Locks section, Spinlocks subsection Note that a thread may not block while holding a spinlock, because that could cause deadlock. Further, preemption is disabled on a given processor while a spinlock is held. However, I haven't been able to locate the code that does this or similar, at least not in osfmk/kern/locks.c. What is the recommended practice on Mac OS X ? I mean, apart from using the lck_ functions, who are not practical to use in my case.

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