From cdc27c27843248ae7eb0df5fc261dd004eaa5670 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Tue, 17 Dec 2013 17:09:08 +0000 Subject: [PATCH] arm64: ptrace: avoid using HW_BREAKPOINT_EMPTY for disabled events Commit 8f34a1da35ae ("arm64: ptrace: use HW_BREAKPOINT_EMPTY type for disabled breakpoints") fixed an issue with GDB trying to zero breakpoint control registers. The problem there is that the arch hw_breakpoint code will attempt to create a (disabled), execute breakpoint of length 0. This will fail validation and report unexpected failure to GDB. To avoid this, we treated disabled breakpoints as HW_BREAKPOINT_EMPTY, but that seems to have broken with recent kernels, causing watchpoints to be treated as TYPE_INST in the core code and returning ENOSPC for any further breakpoints. This patch fixes the problem by prioritising the `enable' field of the breakpoint: if it is cleared, we simply update the perf_event_attr to indicate that the thing is disabled and don't bother changing either the type or the length. This reinforces the behaviour that the breakpoint control register is essentially read-only apart from the enable bit when disabling a breakpoint. Cc: Reported-by: Aaron Liu Signed-off-by: Will Deacon Signed-off-by: Catalin Marinas --- Reading git-format-patch failed