On Fri, 24 Jul 2015 11:41:55 -0700 Linus Torvalds <[email protected]> wrote:
> On Fri, Jul 24, 2015 at 11:29 AM, Linus Torvalds > <[email protected]> wrote: > > > > So in the #DB handler, we would basically only clear instruction > > breakpoints, and only when they trigger. If we have a data breakpoint > > that triggers (even in kernel mode, and with interrupts disabled), let > > it trigger and return with "ret" anyway. No biggie. > > So we'd not only look at "which breakpoint triggered", we'd also look > at the actual debug register and check that "R/Wn == 0", and only > disable it for that case. > > So you'd read %dr6 and %dr7, and then iterate 0..3 and check whether > it triggerd (bit #n in %dr6), and that R/Wn (bits 16-17+n*4 of %dr7) > is zero, and if so, clear LGn bits (bits 0-1+n*2) in %dr7. > > Something like > > unsigned long mask = 0; > unsigned int dr6 = debug_read(6); > unsigned int dr7 = debug_read(7) > int i; > > for (i = 0; i < 4; i++) { > if ((dr6 >> i) & 1) { > if (!((dr7 >> (4*i+16)) & 3)) > mask |= 3 << (i*2); > } > } > > if (mask) > debug_write(dr7 & ~mask, 7); Macros would be nice for readability. for (i = 0; i < 4; i++) { if ((dr6 >> i) & 1) { int shift = DR_CONTROL_SIZE * i + DR_CONTROL_SHIFT; if (!((dr7 >> shift) & DR_RW_READ)) mask |= (DR_LOCAL_ENABLE|DR_GLOBAL_ENABLE) << (i * DR_ENABLE_SIZE); } } -- Steve > > (yeah, I could easily have screwed that up) > > But the above should only clear bits in dr7 that are actually > associated with the instruction breakpoint that triggered, and since > it's a _kernel_ instruction breakpoint, not a user one, we can clear > it and forget it. No need to re-enable at all. > > Hmm? > > Linus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
