Messages in this thread | | | Date | Tue, 26 May 2009 18:40:16 -0700 | From | David Daney <> | Subject | Re: [Patch 01/12] Prepare the code for Hardware Breakpoint interfaces |
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K.Prasad wrote: > 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. >
Sorry, I missed it the first time.
> 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. >
But the comment mentioning all of this is in a generic non-architecture specific file. I do see where it says '...On i386...', so that does clarify it somewhat. Adding something similar to your following explanation ...:
> 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.
... might be worthwhile.
Thanks, David Daney
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