Messages in this thread | | | Date | Mon, 1 May 2006 09:51:27 -0400 | From | Daniel Jacobowitz <> | Subject | Re: [uml-devel] [RFC] PATCH 3/4 - Time virtualization : PTRACE_SYSCALL_MASK |
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On Fri, Apr 28, 2006 at 09:49:56PM -0400, Jeff Dike wrote: > On Fri, Apr 28, 2006 at 10:28:46PM +0200, Blaisorblade wrote: > > Ok, this gives us a definite proposal, which I finally like: > > > > * to exclude sys_tee: > > > > bitmask = 0; > > set_bit(__NR_tee, bitmask); > > ptrace(PTRACE_SET_NOTRACE, bitmask); > > > > * to trace only sys_tee: > > > > bitmask = 0; > > set_bit(__NR_tee, bitmask); > > ptrace(PTRACE_SET_TRACEONLY, bitmask); > > Yup, I like this.
I really recommend you not do this. One (better) suggestion earlier was:
struct { int bitmask_length; int flags; char bitmask[0]; };
The difference between this case and the sigprocmask example is that the size of a sigset_t is very hard to change - it's a userspace ABI break. If you want to model it after sigprocmask, don't look at the man page, which describes the POSIX function. Look at the more recent RT version of the syscall instead:
sys_rt_sigprocmask(int how, sigset_t __user *set, sigset_t __user *oset, size_t sigsetsize)
Suppose the kernel knows about 32 more syscalls than userspace. It's going to read extra bits out of the bitmask that userspace didn't initialize!
Also, if you store the mask with the child process, it risks surprising existing tracers: attach, set mask, detach, then the next time someone attaches an old version of strace some syscalls will be "hidden".
-- Daniel Jacobowitz CodeSourcery - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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