On Sun, 8 Nov 2015 19:37:37 +0000 (UTC) Mathieu Desnoyers <mathieu.desnoy...@efficios.com> wrote:
> I have a few ideas on how to overcome this, and would like your > feedback on the matter: > > 1) One possible approach would be to reserve an extra status flag > in struct thread_info to get the TS_COMPAT status at syscall > entry. It would _not_ be updated when the executable is loaded, > so the state at return from execve would match the state when > entering execve. This is a simple approach, but requires kernel > changes. Or add a flag TS_EXECVE that can be set by the tracepoint syscall enter, and checked on exit. If set, we know that the exec happened. > > 2) Keep the compat state at system call entry in a data structure > (e.g. hash table) indexed by thread number within each tracer. > This could work around this issue within each tracer. This is of course what you can do now. As it doesn't touch the kernel. > > 3) Change the syscall number in the struct pt_regs whenever we > change the compat mode of a process. A 64-bit execve system > call number would be mapped to a 32-bit compat execve number, > or the opposite. This requires a kernel change, and seems to be > rather intrusive. > This is a definite no. I'm thinking the TS_EXECVE flag would be the least intrusive. Add a comment that it is used by tracepoints to map between compat and non-compat syscalls when execve switches the flag. This would not need to touch any of the logic of the hotpaths within the systemcalls themselves. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
