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Message-ID: <20070226235154.GB19630@frankl.hpl.hp.com> Date: Mon, 26 Feb 2007 15:51:54 -0800 From: Stephane Eranian <eranian@....hp.com> To: linux-kernel@...r.kernel.org Cc: linux-ia64@...r.kernel.org, Stephane Eranian <eranian@....hp.com>, ak@...e.de, akpm@...ux-foundation.org, tony.luck@...el.com Subject: debug registers and fork Hello, I have come across an issue with a monitoring using the hardware debug registers on ia64/i386/x86-64. It seems that the way debug registers are inherited across fork differs between ia-64 and i386/x86-64. On ia-64, the debug registers are NEVER inherited in the child. The copy_thread() routine clears the necessary thread flags to avoid reloading the debug registers in the child. Now, on x86-64, it appears that the TIF_DEBUG flag is inherited via setup_thread_stack(). By virtue of dup_task_struct() the debug registers get copied into the child task on fork. So the child has active breakpoints, unless I am mistaken somewhere. Given the way the ptrace() interface works, I would tend to think that the ia-64 way is the correct one. Any comment? Furthermore, on i386/x86-64, when switching out from a task with TIF_DEBUG enabled to another which does not, it seems we do not clear the debug registers (at least dr7) so they become inactive. -- -Stephane - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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