Messages in this thread | | | Date | Tue, 25 Aug 2009 23:08:50 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH v4 0/4] tracing: tweaks for generic syscall events |
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On Tue, Aug 25, 2009 at 10:41:22AM -0400, Jason Baron wrote: > right, the compat layer as well as the core kernel need additional > DEFINE_SYSCALL() macros to catch all the the syscalls. However, I think > the compat layer is a bit more involved in that it often makes use of > the core kernel syscalls, but the mapping between syscall number is > different. So, we need another array, or to augment the existing one, to > cover the compat syscalls. We also need to detect 32-bit processes in > the syscall entry path to determine which array to use, and we need to > grab the arguments differently. So there is a bunch of work here.
Hmm, indeed we may need a parallel compat_syscall_table for the metadata and other kind of special treatements. I wonder how ptrace sort it out in syscall_trace_enter() to guess the origin of the syscall (ia32 or normal), since the table is not mapped with the same numbers.
> Also, we have the question of whether we need separate entries in the > events/syscalls directly for 32-bit process syscalls that call the same > 64-bit syscall interfaces. Should they be parsed as 64-bit argument > values event thought they are 32-bit? To reduce complexity, I would say > the 32-bit syscall entries should be the same as the 64-bit ones. That > said there will be a bunch of new "compat_sys*" etc. entries. >
We could probably re-route the compat syscall tracing to their homologuous 64 bits tracepoints, but one may want to only trace the compat_syscalls, use filters only on them, activate only some of them, etc...
To do such routing, we could have a simple table that resolves a compat syscall number to its real 64 bits syscall number and we could then pass this number plus a flag that set its compat state in the ring buffer entry. That would avoid the need of using the DEFINE_SYSCALLx() in fs/compat.c
But such ghost tracepoints would also complexify too much the filter processing, the individual tracepoints toggling, etc... So I think having real compat tracepoints would actually be more simple.
We could still use shortcuts in userspace if we want to enable sys_enter_open and sys_enter_compat_open at the same time.
Hmm?
> > Is someone willing to cover them? > > > > I can take a stab at it.
Thanks a lot!
> thanks, > > -Jason
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