On Tue, Apr 23, 2013 at 04:18:46PM +0100, Jacob Shin wrote: > On Tue, Apr 23, 2013 at 04:02:40PM +0100, Will Deacon wrote: > > On Tue, Apr 23, 2013 at 03:40:57PM +0100, Jacob Shin wrote: > > > > perf stat -e mem:0x1000/0xf:w a.out > > > > Are you saying that this command would count any write to: > > > > 0x1000 > > 0x1001 > > ... > > 0x100e > > 0x100f > > > > ? > > > > If so, that differs from the ARM debug architecture in that the mask is > > called > > `byte-address-select', so a mask of 0b1001 would count accesses at +0 bytes > > and +3 bytes from the base address. Is that possible to describe with your > > masking scheme and a single watchpoint? > > > > A mask of 0xf, would count +0, +1, +2 and +3 (essentially bp_len == 4). > > > > Unfortunately, that means I can't just invert the mask like I originally > > thought. > > Ah, .. that is different . > > Our hardware matches on the breakpoint if: > > (physical_address & ~bp_addr_mask) == (bp_addr & ~bp_addr_mask) > > In other words, the mask says which of the bp_addr bits hardware should > ignore when matching. > > .. it would be great if we can come up with userland interface that works > for both archs. I'm coming up empty at the moment ..
After a bit of thought, I *think* the ARM mechanism is more expressive, and you could describe your masking in terms of byte-address-select. The downside is that we'd end up with much larger masks, which could be argued as counter-intuitive from a user's point of view. Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
