(2012/03/22 20:57), Jason Wessel wrote: > On 03/21/2012 09:53 PM, Masami Hiramatsu wrote: >> (2012/03/22 2:55), Jason Wessel wrote: >>> There has long been a limitation using software breakpoints with a >>> kernel compiled with CONFIG_DEBUG_RODATA. The kprobe breakpoint code >>> has its own text_poke() function which accommodates writing a >>> breakpoint into a read-only page. The debug_core can make use of the >>> text_poke() capabilities by using the kprobes API, specifically >>> arch_arm_kprobe() and arch_disarm_kprobe(). For now it is safe to use >>> a single statically allocated kprobe structure to call the kprobes API >>> because the debug_core breakpoint API is only used when the kernel is >>> in the debug state. >> >> You might misunderstand it. arch_*_kprobe() are not open APIs. >> Those are kprobes internal APIs (which means that those functions >> should be used only by kprobes). >> > > > I was looking for an interface that solved the problem, without having > to use text_poke directly which is arch specific. Eventually I would > like to use the kprobes high level API, but it cannot not be used > without taking a mutex presently. This is a separate problem to deal > with at a later time, because the generic use of kprobes would be > aimed at having robust single stepping.
I see. >>> The debug_core will first attempt to use the traditional >>> probe_kernel_write(), and next try using a kprobe breakpoint. The >>> kgdb test suite was updated to run all the software breakpoint tests >>> when using a kernel with built with CONFIG_DEBUG_RODATA. >>> >>> Signed-off-by: Jason Wessel <[email protected]> >> >> Nak. >> >> No, please don't use kprobes internal function this way, because >> you can't ensure that the arch_arm_kprobe() has no side-effect. >> >> Why don't you use text_poke()? I see that the text_poke() >> is only for x86, but you already have arch/x86/kernel/kgdb.c for >> making your own wrapper function. > > I will use the arch specific provision to override the > kgdb_arch_set_breakpoint() and use the text_poke() directly. Thanks! that's what I meant. You can use __weak attribute. > Eventually I would like to use the same software breakpoint > reservation system as kprobes, and that would happen if kgdb ever > starts using kprobes for single stepping. Yeah, as far as I can see, current kprobes design assumes that there is no other part uses sw breakpoint in kernel. But there is kgdb now. I think kprobes can share the sw breakpoint instrumentation and single stepping with kgdb. Thank you, -- Masami HIRAMATSU Software Platform Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: [email protected] ------------------------------------------------------------------------------ This SF email is sponsosred by: Try Windows Azure free for 90 days Click Here http://p.sf.net/sfu/sfd2d-msazure _______________________________________________ Kgdb-bugreport mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/kgdb-bugreport
