|From:||Roland McGrath <email@example.com>|
|Subject:||[RFC PATCH 0/4] utrace: new modular infrastructure for user debug/tracing|
|Date:||Tue, 13 Jun 2006 16:10:00 -0700 (PDT)|
I have been working on for a while, and imagining for much longer, replacing ptrace from the ground up. This is what I've come up with so far, and I'm looking for some reactions on the direction. What I'm proposing here is a substrate for doing wonderful new things, and I don't yet have something built on top of it to demonstrate wonderful things. This is intended to make it easy for lots of folks to whip up new things and show what fancy business is possible and worthwhile. I've separated this into four successive patches in hopes it makes it easier to read the patches. The intent is that each intermediate patch yields a kernel tree that compiles and works, though after the first patch and before the last you get ENOSYS from any ptrace call. Patch #1 wipes out ptrace and its cruft from the bowels of the kernel. Patch #2 converts the architecture-specific ptrace guts into the architecture-specific guts for the new thing. Patch #3 is the crux of it, the new layer for writing debugging interfaces. Patch #4 implements ptrace with user ABI compatibility in terms of that layer. These patches are relative to 22.214.171.124; I will shortly rebase to the current 2.6.17ish tree, and post updated patches. I don't think the old base will make it any harder to review the new code in the patches or its core design and implementation choices. There are some known loose ends in the code. I am working on those and will have more updates along with the rebase in a few days. I am seeking feedback on the patches now to identify more issues I have not already noted in the code. These changes require some small porting work for each architecture. In these patches, I have done the architecture work only for i386, x86_64, and powerpc. The machine-specific work is quite small and straightforward for anyone even mildly familiar with the architecture in question. It consists mainly of rearranging the existing architecture code used for ptrace into some new functions. There should be no need for new assembly hacking or anything like that. I was able to do the powerpc support in a couple of hours, and am not any kind of expert on ppc (and took quite a bit longer just to get myself able to build and boot ppc kernels). Anyone interested in doing the architecture support for another machine, please contact me and I'll be glad to help. The steps might already be fairly obvious from reading the arch/ changes in these patches. At http://redhat.com/~roland/utrace/ you can always find the current state of this work. There you can also find a small test suite I use, and an example module demonstrating a novel feature implemented very cheaply using the new infrastructure. Please send feedback to me at <firstname.lastname@example.org>. I've tested the new kernel APIs directly with the aforementioned (tiny) test suite, and tested them more thoroughly by testing the ptrace compatibility implementation based on them. That I've tested using the gdb test suite, on x86_64 and ppc64 for both 32-bit and 64-bit userland (including both 32-bit and 64-bit gdb's debugging 32-bit processes on the 64-bit kernel), and on i386. I have not tested the ppc32 kernel, but it builds and the changed code is mostly shared with the ppc64 code that does work, so it has a decent chance. (For other architectures, some work is still required even to get the kernel building again.) --- This series of patches revamps the support for user process debugging from the ground up, replacing the old ptrace support completely. Two major problems with ptrace are its interface and its implementation. The low-level code for tracing core events is directly tied into the implementation of the ptrace system call interface. Machine-dependent code for accessing registers and controlling single-stepping is intermingled with core implementation details that are actually machine-independent and repeated across arch directories. ptrace interferes with the normal parent-child linkage, introducing many corner cases that have caused trouble in the past. The shortcomings of ptrace as a user-mode interface for debugging are many, and well-known to those who have worked with it from the userland side, or been involved in fixing and maintaining it in the kernel. The system call interface is clunky to use and to extend, and makes it difficult to reduce the overhead of doing several operations and of transferring large amounts of data. There is no way for more than one party to trace a process. The reporting model using SIGCHLD and wait4 is tricky to use reliably from userland, and especially hard to integrate with other kinds of event loop. Thread event reporting is heavy-weight and not specified with good granularity: in practice a traced thread stops for everything. The old ptrace implementation is removed entirely and replaced with a modular interface layer that provides user debugging and tracing functionality separate from any single userland interface. Rather than trying to come up with a single new interface to replace ptrace, this provides a platform for higher-level code in kernel modules to provide userland interfaces for tracing and debugging. The ptrace system call is provided for compatibility, written on top of the new modular layer. Currently there are these four patches: [PATCH 1] utrace: tracehook (die, ptrace, die) [PATCH 2] utrace: register sets [PATCH 3] utrace core [PATCH 4] utrace: ptrace compatibility Thanks, Roland - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to email@example.com More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Copyright © 2006, Eklektix, Inc.
Comments and public postings are copyrighted by their creators.
Linux is a registered trademark of Linus Torvalds