Messages in this thread | | | Date | Fri, 22 May 2009 11:48:27 +0530 | From | "K.Prasad" <> | Subject | Re: [Patch 01/12] Prepare the code for Hardware Breakpoint interfaces |
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On Thu, May 21, 2009 at 09:16:38AM -0700, David Daney wrote: > K.Prasad wrote: > [...] >> +struct hw_breakpoint { >> + void (*triggered)(struct hw_breakpoint *, struct pt_regs *); >> + struct arch_hw_breakpoint info; >> +}; >> +/* >> + * len and type values are defined in include/asm/hw_breakpoint.h. >> + * Available values vary according to the architecture. On i386 the >> + * possibilities are: >> + * >> + * HW_BREAKPOINT_LEN_1 >> + * HW_BREAKPOINT_LEN_2 >> + * HW_BREAKPOINT_LEN_4 >> + * HW_BREAKPOINT_RW >> + * HW_BREAKPOINT_READ >> + * >> + * On other architectures HW_BREAKPOINT_LEN_8 may be available, and the >> + * 1-, 2-, and 4-byte lengths may be unavailable. There also may be >> + * HW_BREAKPOINT_WRITE. You can use #ifdef to check at compile time. >> + */ >> + > > I question weather having all these symbols for lengths is the proper > approach. > > On mips we would currently have: > > HW_BREAKPOINT_LEN_8 > HW_BREAKPOINT_LEN_16 > HW_BREAKPOINT_LEN_32 > HW_BREAKPOINT_LEN_64 > HW_BREAKPOINT_LEN_128 > HW_BREAKPOINT_LEN_256 > HW_BREAKPOINT_LEN_512 > HW_BREAKPOINT_LEN_1024 > HW_BREAKPOINT_LEN_2048 > > If we were to use a debug agent hooked into the MIPS EJTAG debugger > support registers, 63 different even powers of 2 are valid lengths. > > Determining the range of allowed breakpoint lengths, converting back > and forth between numeric values that are likely to be used in a > debugger, and these symbolic values that the proposed kernel interface > would use, could be a little ugly. > > Have you thought about passing just the raw length? And perhaps > having: > > HW_BREAKPOINT_LEN_MASK that would have a bit set for each log2 of a > legal length? >
As explained to you here: http://lkml.org/lkml/2008/12/16/553/, defining every possible length of the HW Breakpoint works for x86, but may not be suitable for MIPS.
As you might have seen, the HW_BREAKPOINT_LEN_* values are defined in x86-specific files and will be compared against 'len' field in arch-specific 'struct arch_hw_breakpoint', for the reason that these attributes are not valid for all architectures and have to be defined for each processor in their own way.
Defining a HW_BREAKPOINT_LEN_MASK mask and validation of the input length to check if it is a valid power of 2 can still be done for MIPS in the arch-specific files and I don't see any part of the generic interface being a hurdle during its implementation. Let me know if you think there's any.
> Or perhaps add a function to the interface that would validate the > length? >
arch_validate_hwbkpt_settings() invoked during register_<kernel>/<user>_hw_breakpoint() is that function which validates the length.
> David Daney
Thanks, K.Prasad
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