LoongArch: ptrace: Add hardware single step support

Use the generic ptrace_resume code for PTRACE_SYSCALL, PTRACE_CONT,
PTRACE_KILL and PTRACE_SINGLESTEP handling. This implies defining
arch_has_single_step() and implementing the user_enable_single_step()
and user_disable_single_step() functions.

LoongArch cannot do hardware single-stepping per se, the hardware
single-stepping it is achieved by configuring the instruction fetch
watchpoints (FWPS) and specifies that the next instruction must trigger
the watch exception by setting the mask bit. In some scenarios
CSR.FWPS.Skip is used to ignore the next hit result, avoid endless
repeated triggering of the same watchpoint without canceling it.

Signed-off-by: Qing Zhang <zhangqing@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

1 files changed, 70 insertions, 0 deletions

diff --git a/arch/loongarch/kernel/ptrace.c b/arch/loongarch/kernel/ptrace.c
index 11b491395636..06bceae7d104 100644
--- a/arch/loongarch/kernel/ptrace.c
+++ b/arch/loongarch/kernel/ptrace.c
@@ -31,6 +31,7 @@
 #include <linux/smp.h>
 #include <linux/stddef.h>
 #include <linux/seccomp.h>
+#include <linux/thread_info.h>
 #include <linux/uaccess.h>
 
 #include <asm/byteorder.h>
@@ -41,6 +42,7 @@
 #include <asm/page.h>
 #include <asm/pgtable.h>
 #include <asm/processor.h>
+#include <asm/ptrace.h>
 #include <asm/reg.h>
 #include <asm/syscall.h>
 
@@ -833,3 +835,71 @@ long arch_ptrace(struct task_struct *child, long request,
 
 	return ret;
 }
+
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+static void ptrace_triggered(struct perf_event *bp,
+		      struct perf_sample_data *data, struct pt_regs *regs)
+{
+	struct perf_event_attr attr;
+
+	attr = bp->attr;
+	attr.disabled = true;
+	modify_user_hw_breakpoint(bp, &attr);
+}
+
+static int set_single_step(struct task_struct *tsk, unsigned long addr)
+{
+	struct perf_event *bp;
+	struct perf_event_attr attr;
+	struct arch_hw_breakpoint *info;
+	struct thread_struct *thread = &tsk->thread;
+
+	bp = thread->hbp_break[0];
+	if (!bp) {
+		ptrace_breakpoint_init(&attr);
+
+		attr.bp_addr = addr;
+		attr.bp_len = HW_BREAKPOINT_LEN_8;
+		attr.bp_type = HW_BREAKPOINT_X;
+
+		bp = register_user_hw_breakpoint(&attr, ptrace_triggered,
+						 NULL, tsk);
+		if (IS_ERR(bp))
+			return PTR_ERR(bp);
+
+		thread->hbp_break[0] = bp;
+	} else {
+		int err;
+
+		attr = bp->attr;
+		attr.bp_addr = addr;
+
+		/* Reenable breakpoint */
+		attr.disabled = false;
+		err = modify_user_hw_breakpoint(bp, &attr);
+		if (unlikely(err))
+			return err;
+
+		csr_write64(attr.bp_addr, LOONGARCH_CSR_IB0ADDR);
+	}
+	info = counter_arch_bp(bp);
+	info->mask = TASK_SIZE - 1;
+
+	return 0;
+}
+
+/* ptrace API */
+void user_enable_single_step(struct task_struct *task)
+{
+	struct thread_info *ti = task_thread_info(task);
+
+	set_single_step(task, task_pt_regs(task)->csr_era);
+	task->thread.single_step = task_pt_regs(task)->csr_era;
+	set_ti_thread_flag(ti, TIF_SINGLESTEP);
+}
+
+void user_disable_single_step(struct task_struct *task)
+{
+	clear_tsk_thread_flag(task, TIF_SINGLESTEP);
+}
+#endif