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> Davide's patch (which has been in -mm for 6-7 weeks) doesn't add > fastpath overhead. I am also dubious about exactly what it does. That patch seems a bizarre obfuscation of the code to me. TIF_SINGLESTEP is really there to handle the lazy TF clearing for sysenter entry, and that's all. I don't think that patch handles user-mode setting TF properly, unusual though that case is. How does that patch interact with PT_TRACESYSGOOD? It appears to me that PTRACE_SINGLESTEP will now generate a syscall trap instead of a single-step trap, which is an undesireable change in behavior I would say. I don't really care about user-mode setting of TF before executing int $0x80. If poeple have programs that use TF in user mode, they have never complained about the issue before. For PTRACE_SINGLESTEP, Davide's approach of setting the kernel-work flag directly when PTRACE_SINGLESTEP sets TF in the user flags word is the obvious way to avoid the test in the fast path. I am inclined to combine that approeach with what my patch does, i.e. just take out the system call fast-path test and set TIF_SINGLESTEP_TRAP in PTRACE_SINGLESTEP. I think the way Davide's patch uses TIF_SINGLESTEP is pretty questionable. Thanks, Roland - 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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