Messages in this thread | | | Date | Wed, 25 May 2005 18:06:52 -0700 | From | Keshavamurthy Anil S <> | Subject | Re: [patch 1/4] Kprobes support for IA64 |
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On Thu, May 26, 2005 at 10:49:02AM +1000, Keith Owens wrote: > On Wed, 25 May 2005 10:00:18 -0400, > "Alan D. Brunelle" <Alan.Brunelle@hp.com> wrote: > >Isn't the real issue here that if kprobes attempts to put in a 'break > >0x80200' into a B-slot that it instead becomes a 'break.b 0' -- as the > >break.b does not accept an immediate value? > > break.b is a B9 type instruction, which does take an imm21 value. It > is the hardware that does not store imm21 in CR.IIM when break.b is > issued. > > >Kprobes does have the two cases covered in traps.c (case 0 - when a > >B-slot break is used, and case 0x80200 for a non-B-slot break). But this > >doesn't seem very clean. (If it was decided that one should not overload > >the break 0 case, and instead use a uniquely defined break number, then > >it fails on a B-slot probe. If it is OK to overload the break 0 case, > >why have another break number at all?) > > Mainly for documentation when looking at the assembler code. break 0 > is used for BUG(), coding a different value in the break instruction > for the debugger helps the person debugging the debugger :(. I have no > problem with coding two cases in ia64_bad_break() in order to work > around the hardware "feature".
I agree with Keith, when a person taking a instructin dump, a different value will help uniquely identify that this is a kprobe break instruction which is a replaced instrucion of the original instruction. So we will leave with what we have now, i.e handle the same with two cases.
> > Also consider the case where your debugger allows users to code a > deliberate entry to the debugger, like KDB_ENTER(). That case always > requires a separate break imm21 value, because the break point is not > known to the debugger until the code is executed. > - 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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