The data formatter in lldb is a subsystem that allows users to define custom display options, the Platform is the agent that provides a way to work with a specific platform. I agree that we need the Platform to provide the OS specific data formatters, but also the Platform should have a functionality to find all OS mutexes, am I right?
On Thu, Nov 1, 2018 at 7:37 PM Jim Ingham <jing...@apple.com> wrote: > I don’t think we are disagreeing, probably I was just being a little too > terse. What I’m saying is that to PRESENT a mutex in some detail, we need > an OS specific data formatter, so in that case, we just need some agent, > either the Platform or the SystemRuntime (but the Platform seems better to > me for this) to provide the OS specific data formatters. But we don’t need > a new facility for that, just a way to dial up the right OS-specific > instances. And if we can reuse more general features to present this sort > of OS specific info we are better off; it reduces lldb’s surface area and > provides facilities we might find other neat ways to use. > > OTOH, for a runtime feature like “Gather all the mutexes currently in > flight” we would need some new code. There’s nothing in lldb that does > that sort of job. The SystemRuntime seems like the right place for that > code to go. > > Jim > > > On Nov 1, 2018, at 1:25 AM, Alexander Polyakov <polyakov....@gmail.com> > wrote: > > I'm new in plugin ecosystem, so I have some misunderstanding. You wrote > that to comprehend mutexes we just need a data formatter, but how can we > get the raw data of all mutexes in our OS? I thought I was supposed to > write a generic code that will use a user-defined (specific for each OS) > way to collect all mutexes and then use some data formatter to show them. > > On Thu, Nov 1, 2018 at 2:31 AM Jim Ingham <jing...@apple.com> wrote: > >> As Jason pointed out, we also have the SystemRuntime Plugin. That is >> intended to provide extra runtime available information based on the >> current system. For instance, on Darwin we use it to present the >> libdispatch queue view of threads on the system, and to decorate threads >> that are doing work on behalf of some queue with the state of the thread >> that enqueued the work at the time the work item was enqueued. >> >> If for instance you had a way to gather all the locks in the process >> (something we've been asked to do but I don't know how to do it on >> Darwin...), that would be the place to put that functionality. >> >> Jim >> >> >> > On Oct 31, 2018, at 4:05 PM, Jim Ingham via lldb-dev < >> lldb-dev@lists.llvm.org> wrote: >> > >> > Right now, the OS plugin only supports the job of adding threads. And >> that makes more sense as a plugin, because for instance if you had a >> cooperative threading scheme that you were laying on top of the system >> threads in a User Space process, you can use the Operating System plugin to >> show you the cooperative threads. This is not an abstract example... I >> think it should stay with just that job. >> > >> > The place where lldb holds this sort of knowledge is supposed to be in >> the Platform class. So for instance, to comprehend mutexes you really just >> need a data formatter. The trick is that it has to be a data formatter >> that is provided by the platform. Similarly you want to have frame >> recognizers for interesting lower-level calls in the system. The machinery >> will shortly be there to do that, but loading the particular recognizers >> will either need to be done by hand, or coordinated by the Platform. In >> general, I think most of the kinds of re-presentation you need to do to >> make OS objects and processes more comprehensible can be built as general >> mechanisms like the above. Then the Platform can coordinate providing the >> set of more general transformations that are appropriate to the Platform >> you are targeting. >> > >> > Jim >> > >> > >> > >> >> On Oct 31, 2018, at 3:44 PM, Alexander Polyakov < >> polyakov....@gmail.com> wrote: >> >> >> >> So, if I understand you write, I can look at OS plugin and add a >> support of mutexes or memory pages for example? >> >> >> >> чт, 1 нояб. 2018 г. в 1:05, Jim Ingham <jing...@apple.com>: >> >> lldb has one feature - the "Operating System Plugin" that is >> specifically designed for debugging threads in kernel contexts. The OS >> plugin allows a kernel to present it's notion of threads into >> lldb_private::Threads. The xnu kernel macros have an implementation of >> this, as do some other embedded OS'es. lldb actually gets used pretty >> extensively for debugging xnu - the Darwin kernel. >> >> >> >> Kuba is adding the notion of "Frame recognizers" which can give >> significance to particular functions when they appear on the stack (for >> instance displaying the first argument of read, etc. as a file handle even >> if you have no debug information for it.) That's another way that you >> could express your understanding of the OS you are running on for debugger >> users. Greg wrote a data formatter for the Darwin implementation of >> pthread_mutex that shows the thread that has the lock and some other >> information like that. So data formatters are also a way lldb can express >> knowledge of the host OS. >> >> >> >> Jim >> >> >> >>> On Oct 31, 2018, at 12:52 PM, Leonard Mosescu via lldb-dev < >> lldb-dev@lists.llvm.org> wrote: >> >>> >> >>> Conceptually it's different levels of abstraction: a user-mode >> debugger handles processes, threads as first class concepts. In kernel-mode >> (or kernel land), these are just data structures that the code (the kernel) >> is managing. From a more pragmatic perspective, the difference is in where >> the debugging hooks are implemented and what interfaces are exposed (for >> example a kernel mode debugger can normally "poke" around any piece of >> memory and it has to be aware of things like VA mappings, while a user-mode >> debugger is only allowed to control a limited slice of the system - ex. >> control a sub-process through something like ptrace) >> >>> >> >>> Unless you're specifically looking at kernel debugging I'd stay away >> from that. For one thing, LLDB is mostly used as an user-mode debugger so >> the impact of any improvements would be bigger. >> >>> >> >>> Regarding the value of OS-awareness for user-mode debugging, I agree >> with Zach - for example windbg provides both kernel mode and user mode >> !locks commands. The only suggestion I'd add is to consider an expanded >> view of the "OS" to include runtime components which may not be technically >> part of what most people think of as the "OS": user-mode loaders and high >> level things like std::mutex, etc. >> >>> >> >>> On Wed, Oct 31, 2018 at 12:29 PM, Alexander Polyakov < >> polyakov....@gmail.com> wrote: >> >>> Looks like I don't completely understand what is the difference >> between user-mode and kernel-mode from the debugger's point of view. Could >> you please explain me this? >> >>> >> >>> On Wed, Oct 31, 2018 at 10:22 PM Zachary Turner <ztur...@google.com> >> wrote: >> >>> I don’t totally agree with this. I think there are a lot of useful os >> awareness tasks in user mode. For example, you’re debugging a deadlock and >> want to understand the state of other mutexes, who owns them, etc. or you >> want to examine open file descriptors. In the case of a heap corruption you >> may wish to study the internal structures of your process’s heap, or even >> lower level, the os virtual memory page table structures. >> >>> >> >>> There’s quite a lot you can still do in user mode, but definitely >> there is more in kernel mode. As Leonard said, try put WinDbg as a lot of >> this stuff already exists so it’s a good reference >> >>> On Wed, Oct 31, 2018 at 12:08 PM Alexander Polyakov via lldb-dev < >> lldb-dev@lists.llvm.org> wrote: >> >>> Hi Leonard, >> >>> >> >>> I think it will be kernel-mode debugging since debugging an >> application in user mode is not an OS awareness imo. Of course, some of >> kernel's modules might run in user-mode, but it will be ok I think. >> >>> >> >>> Thanks for your reference, I'll take a look at it. >> >>> >> >>> Also, I found out that ARM supports OS awareness in their DS-5 >> debugger. They have a mechanism for adding new operating systems. All you >> need to do is to describe OS' model (thread's or task's structure for >> example). I think that is how it might be done in LLDB. >> >>> >> >>> On Wed, Oct 31, 2018 at 9:26 PM Leonard Mosescu <mose...@google.com> >> wrote: >> >>> Hi Alexander, are you interested in user-mode, kernel-mode debugging >> or both? >> >>> >> >>> Fore reference, the current state of the art regarding OS-awareness >> debugging is debugging tools for windows (windbg & co.). This is not >> surprising since the tools were developed alongside Windows. Obviously they >> are specific to Windows, but it's good example of how the OS-awareness >> might look like. >> >>> >> >>> >> >>> On Mon, Oct 29, 2018 at 11:37 AM, Alexander Polyakov via lldb-dev < >> lldb-dev@lists.llvm.org> wrote: >> >>> Hi lldb-dev, >> >>> >> >>> I'm a senior student at Saint Petersburg State University. The one of >> my possible diploma themes is "OS Awareness in LLDB". Generally, the OS >> awareness extends a debugger to provide a representation of the OS threads >> - or tasks - and other relevant data structures, typically semaphores, >> mutexes, or queues. >> >>> >> >>> I want to ask the community if OS awareness is interesting for LLDB >> users and developers? The main goal is to create some base on top of LLDB >> that can be extended to support awareness for different operating systems. >> >>> >> >>> Also, if you have a good article or other useful information about OS >> awareness, please share it with me. >> >>> >> >>> Thanks in advance! >> >>> >> >>> -- >> >>> Alexander >> >>> >> >>> _______________________________________________ >> >>> lldb-dev mailing list >> >>> lldb-dev@lists.llvm.org >> >>> http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev >> >>> >> >>> >> >>> >> >>> >> >>> -- >> >>> Alexander >> >>> _______________________________________________ >> >>> lldb-dev mailing list >> >>> lldb-dev@lists.llvm.org >> >>> http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev >> >>> >> >>> >> >>> -- >> >>> Alexander >> >>> >> >>> _______________________________________________ >> >>> lldb-dev mailing list >> >>> lldb-dev@lists.llvm.org >> >>> http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev >> >> >> >> -- >> >> Alexander >> > >> > _______________________________________________ >> > lldb-dev mailing list >> > lldb-dev@lists.llvm.org >> > http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev >> >> > > -- > Alexander > > > -- Alexander
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