Justus Winter <4win...@informatik.uni-hamburg.de> skribis: > Quoting Ludovic =?utf-8?Q?Court=C3=A8s?= (2013-09-10 20:00:32) >> Justus Winter <4win...@informatik.uni-hamburg.de> skribis: >> >> > Quoting Samuel Thibault (2013-09-09 19:40:23) >> >> Ludovic Courtès, le Mon 09 Sep 2013 18:48:03 +0200, a écrit : >> >> > Samuel Thibault <samuel.thiba...@gnu.org> skribis: >> >> > > Ludovic Courtès, le Sat 07 Sep 2013 22:04:06 +0200, a écrit : >> >> > >> However, wouldn’t it be preferable to fix it by interposing on >> >> > >> ‘task_create’ calls, à la clans & chiefs? (IIUC, this can be done >> >> > >> with >> >> > >> by setting the TASK_KERNEL_PORT of a task.) >> >> > > >> >> > > Apparently task_create is a kernel trap. >> >> > >> >> > Isn’t rpctrace able to interpose on it? >> >> >> >> I don't think there is any way to interpose a trap. >> >> >> >> It probably happens that libc nicely uses the RPC, but nothing prevents >> >> a process from raising a trap. >> > >> > As I understand [0] one can interpose all Mach system calls >> >> Yes, and ‘task_create’ is no exception to the rule: >> >> --8<---------------cut here---------------start------------->8--- >> ludo@darnassus:~$ rpctrace -o ,,s sh -c 'sleep 2 & true' > > This is all very fascinating, but completely unrelated. Have you > looked at [0]? Have you looked at rpctrace?
(Please let’s keep the tone cordial, we’re both trying to be constructive, I think.) I was not referring to syscall emulation, but to ‘task_set_special_port’ with the TASK_KERNEL_PORT flag, which is how rpctrace interposes on all RPCs including those normally served by the kernel, IIUC. >> So what about using that technique to achieve what you want? :-) > > Besides me having second thoughts about using this on every process on > the system (this is the part of my message that you conveniently left > out while quoting btw)? You wrote: Then again, I do not think it is meant as a mechanism to change the semantic of one system call for all processes and I do not know the performance implications of this mechanism. In the case we discuss here, the semantics of ‘task_create’ would be preserved. There’s surely a performance impact, that would have to be measured. Now, how bad is it compared to, say, calling user-space ethernet drivers vs. in-kernel drivers? :-) > Well, if anyone can set the emulation vector, how do you prevent any > process from clearing your interception function? By intercepting the > setting of the emulation vector and replicating the emulation > yourself? Yes, or just by making it a no-op, no? (I think the problem also arises with the patch your proposed, no?) Thanks, Ludo’.
