From mboxrd@z Thu Jan 1 00:00:00 1970 From: panand@redhat.com (Pratyush Anand) Date: Tue, 7 Jun 2016 12:25:20 +0530 Subject: Support for unaligned watchpoints in arm/arm64 In-Reply-To: <20160531123827.GF24936@arm.com> References: <20160531123827.GF24936@arm.com> Message-ID: <20160607065520.GD13643@dhcppc6> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 31/05/2016:01:38:27 PM, Will Deacon wrote: > On Thu, May 26, 2016 at 05:04:46PM +0100, Pavel Labath wrote: > > Hello all, > > Hi Pavel, > > > I've been wondering if there are any plans about adding support for > > unaligned watchpoints to the kernel. It seems quite a shame that > > applications are not able not use them, even though the hardware > > should support that feature. > > I'm actually coming round to the idea of ditching the perf hw_breakpoint > mechanism entirely and simply writing a ptrace back-end that can expose > the hardware features directly to userspace. The two issues with this > are: > > (1) It's a fair amount of work So, by the time this new interface would come, probably we can consider a fixup like following to resolve this issue at hand. Probably, things should work by just allowing hw_breakpoint.c to pass checks for unaligned offset when it is a WATCHPOINT, no? diff --git a/arch/arm64/kernel/hw_breakpoint.c b/arch/arm64/kernel/hw_breakpoint.c index 26a6bf77d272..c803347c1413 100644 --- a/arch/arm64/kernel/hw_breakpoint.c +++ b/arch/arm64/kernel/hw_breakpoint.c @@ -384,7 +384,12 @@ int arch_bp_generic_fields(struct arch_hw_breakpoint_ctrl ctrl, *gen_len = HW_BREAKPOINT_LEN_8; @@ -384,7 +384,12 @@ int arch_bp_generic_fields(struct arch_hw_breakpoint_ctrl ctrl, *gen_len = HW_BREAKPOINT_LEN_8; break; default: - return -EINVAL; + if (ctrl.type == ARM_BREAKPOINT_EXECUTE + || ctrl.len & (ctrl.len + 1) + || ctrl.len < ARM_BREAKPOINT_LEN_1 + || ctrl.len > ARM_BREAKPOINT_LEN_8) + return -EINVAL; + *gen_len = ffs(ctrl.len + 1) - 1; } return 0; @@ -430,7 +435,11 @@ static int arch_build_bp_info(struct perf_event *bp) info->ctrl.len = ARM_BREAKPOINT_LEN_8; break; default: - return -EINVAL; + if (info->ctrl.type == ARM_BREAKPOINT_EXECUTE + || bp->attr.bp_len < HW_BREAKPOINT_LEN_1 + || bp->attr.bp_len > HW_BREAKPOINT_LEN_8) + return -EINVAL; + info->ctrl.len = (1 << bp->attr.bp_len) - 1; } /* @Pavel, does above patch helps to resolve the issue. ~Pratyush > (2) We might already have users of the perf interface (including compat) > > I'm really not happy with the way hw_breakpoint worked out :( > > Will > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel at lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel