xtensa: support hardware breakpoints/watchpoints

Use perf framework to manage hardware instruction and data breakpoints.
Add two new ptrace calls: PTRACE_GETHBPREGS and PTRACE_SETHBPREGS to
query and set instruction and data breakpoints.
Address bit 0 choose instruction (0) or data (1) break register, bits
31..1 are the register number.
Both calls transfer two 32-bit words: address (0) and control (1).
Instruction breakpoint contorl word is 0 to clear breakpoint, 1 to set.
Data breakpoint control word bit 31 is 'trigger on store', bit 30 is
'trigger on load, bits 29..0 are length. Length 0 is used to clear a
breakpoint. To set a breakpoint length must be a power of 2 in the range
1..64 and the address must be length-aligned.

Introduce new thread_info flag: TIF_DB_DISABLED. Set it if debug
exception is raised by the kernel code accessing watched userspace
address and disable corresponding data breakpoint. On exit to userspace
check that flag and, if set, restore all data breakpoints.

Handle debug exceptions raised with PS.EXCM set. This may happen when
window overflow/underflow handler or fast exception handler hits data
breakpoint, in which case save and disable all data breakpoints,
single-step faulting instruction and restore data breakpoints.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

1 files changed, 4 insertions, 5 deletions

diff --git a/arch/xtensa/include/asm/processor.h b/arch/xtensa/include/asm/processor.h
index 744ecf0dc3a4..d2e40d39c615 100644
--- a/arch/xtensa/include/asm/processor.h
+++ b/arch/xtensa/include/asm/processor.h
@@ -130,11 +130,10 @@ struct thread_struct {
 	unsigned long bad_vaddr; /* last user fault */
 	unsigned long bad_uaddr; /* last kernel fault accessing user space */
 	unsigned long error_code;
-
-	unsigned long ibreak[XCHAL_NUM_IBREAK];
-	unsigned long dbreaka[XCHAL_NUM_DBREAK];
-	unsigned long dbreakc[XCHAL_NUM_DBREAK];
-
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+	struct perf_event *ptrace_bp[XCHAL_NUM_IBREAK];
+	struct perf_event *ptrace_wp[XCHAL_NUM_DBREAK];
+#endif
 	/* Make structure 16 bytes aligned. */
 	int align[0] __attribute__ ((aligned(16)));
 };