[PATCH v2 2/3] LoongArch: Add ptrace single step support

[Qing Zhang]

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

LongArch has no hardware single-step register. the hardware single-step
function multiplex fetch instruction watchpoint(FWPS) and specifies that
the next instruction must trigger the watch exception by setting the mask bit.

Signed-off-by: Qing Zhang <zhangqing@xxxxxxxxxxx>
---
 arch/loongarch/include/asm/hw_breakpoint.h |  2 +-
 arch/loongarch/include/asm/ptrace.h        |  2 +
 arch/loongarch/kernel/hw_breakpoint.c      | 31 ++++++++--
 arch/loongarch/kernel/ptrace.c             | 68 ++++++++++++++++++++++
 arch/loongarch/kernel/traps.c              | 29 ++++++---
 5 files changed, 119 insertions(+), 13 deletions(-)

diff --git a/arch/loongarch/include/asm/hw_breakpoint.h b/arch/loongarch/include/asm/hw_breakpoint.h
index 44c109f0517f..c1dc450acabb 100644
--- a/arch/loongarch/include/asm/hw_breakpoint.h
+++ b/arch/loongarch/include/asm/hw_breakpoint.h
@@ -1,6 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 /*
- * Copyright (C) 2022 Loongson Technology Corporation Limited
+ * Copyright (C) 2022-2023 Loongson Technology Corporation Limited
  */
 #ifndef __ASM_HW_BREAKPOINT_H
 #define __ASM_HW_BREAKPOINT_H
diff --git a/arch/loongarch/include/asm/ptrace.h b/arch/loongarch/include/asm/ptrace.h
index 58596c4f8a0f..66a0e6c480a3 100644
--- a/arch/loongarch/include/asm/ptrace.h
+++ b/arch/loongarch/include/asm/ptrace.h
@@ -150,4 +150,6 @@ static inline void user_stack_pointer_set(struct pt_regs *regs,
 	regs->regs[3] = val;
 }
 
+#define arch_has_single_step()		(1)
+
 #endif /* _ASM_PTRACE_H */
diff --git a/arch/loongarch/kernel/hw_breakpoint.c b/arch/loongarch/kernel/hw_breakpoint.c
index 509af6c54bed..39b21a2795a0 100644
--- a/arch/loongarch/kernel/hw_breakpoint.c
+++ b/arch/loongarch/kernel/hw_breakpoint.c
@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 /*
- * Copyright (C) 2022 Loongson Technology Corporation Limited
+ * Copyright (C) 2022-2023 Loongson Technology Corporation Limited
  */
 #define pr_fmt(fmt) "hw-breakpoint: " fmt
 
@@ -153,6 +153,20 @@ static int hw_breakpoint_slot_setup(struct perf_event **slots, int max_slots,
  */
 void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
 {
+	int i;
+	struct thread_struct *t = &tsk->thread;
+
+	for (i = 0; i < LOONGARCH_MAX_BRP; i++) {
+		if (t->hbp_break[i]) {
+			 t->hbp_break[i] = NULL;
+		}
+	}
+
+	for (i = 0; i < LOONGARCH_MAX_WRP; i++) {
+		if (t->hbp_watch[i]) {
+			t->hbp_watch[i] = NULL;
+		}
+	}
 }
 
 void ptrace_hw_copy_thread(struct task_struct *tsk)
@@ -498,9 +512,18 @@ arch_initcall(arch_hw_breakpoint_init);
 void hw_breakpoint_thread_switch(struct task_struct *next)
 {
 	struct pt_regs *regs = task_pt_regs(next);
-
-	/* Update breakpoints/watchpoints. */
-	update_bp_registers(regs, 1);
+	u64 addr, mask;
+
+	if (test_bit(TIF_SINGLESTEP, &task_thread_info(next)->flags)) {
+		addr = read_wb_reg(CSR_CFG_ADDR, 0, 0);
+		mask = read_wb_reg(CSR_CFG_MASK, 0, 0);
+		if ((task_pt_regs(next)->csr_era & ~mask) == (addr & ~mask))
+			csr_write32(0x10000, LOONGARCH_CSR_FWPS);
+		regs->csr_prmd |= CSR_PRMD_PWE;
+	} else {
+		/* Update breakpoints/watchpoints. */
+		update_bp_registers(regs, 1);
+	}
 }
 
 void hw_breakpoint_pmu_read(struct perf_event *bp)
diff --git a/arch/loongarch/kernel/ptrace.c b/arch/loongarch/kernel/ptrace.c
index bee4194177fd..52a3ee4366f4 100644
--- a/arch/loongarch/kernel/ptrace.c
+++ b/arch/loongarch/kernel/ptrace.c
@@ -20,6 +20,7 @@
 #include <linux/context_tracking.h>
 #include <linux/elf.h>
 #include <linux/errno.h>
+#include <linux/hw_breakpoint.h>
 #include <linux/mm.h>
 #include <linux/ptrace.h>
 #include <linux/regset.h>
@@ -30,6 +31,7 @@
 #include <linux/stddef.h>
 #include <linux/seccomp.h>
 #include <linux/uaccess.h>
+#include <linux/thread_info.h>
 
 #include <asm/byteorder.h>
 #include <asm/cpu.h>
@@ -39,6 +41,7 @@
 #include <asm/page.h>
 #include <asm/pgtable.h>
 #include <asm/processor.h>
+#include <asm/ptrace.h>
 #include <asm/reg.h>
 #include <asm/syscall.h>
 
@@ -541,3 +544,68 @@ long arch_ptrace(struct task_struct *child, long request,
 
 	return ret;
 }
+
+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 thread_struct *thread = &tsk->thread;
+	struct perf_event *bp;
+	struct perf_event_attr attr;
+	struct arch_hw_breakpoint *info;
+
+	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 = 0xffffffffffff;
+
+	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);
+}
diff --git a/arch/loongarch/kernel/traps.c b/arch/loongarch/kernel/traps.c
index 70085d83476d..2368ff9d4ab2 100644
--- a/arch/loongarch/kernel/traps.c
+++ b/arch/loongarch/kernel/traps.c
@@ -508,18 +508,31 @@ asmlinkage void noinstr do_bp(struct pt_regs *regs)
 
 asmlinkage void noinstr do_watch(struct pt_regs *regs)
 {
-	enum ctx_state prev_state;
+	irqentry_state_t state = irqentry_enter(regs);
 
-	prev_state = exception_enter();
+	if (test_tsk_thread_flag(current, TIF_SINGLESTEP)) {
+		int llbit = (csr_read32(LOONGARCH_CSR_LLBCTL) & 0x1);
+		unsigned long pc = regs->csr_era;
 
+		if (llbit) {
+			csr_write32(0x10000, LOONGARCH_CSR_FWPS);
+			csr_write32(0x4, LOONGARCH_CSR_LLBCTL);
+		} else if (pc == current->thread.single_step) {
+			csr_write32(0x10000, LOONGARCH_CSR_FWPS);
+		} else {
+			force_sig(SIGTRAP);
+		}
+	} else {
 #ifdef CONFIG_HAVE_HW_BREAKPOINT
-	if (breakpoint_handler(regs))
-		return;
-	if (watchpoint_handler(regs))
-		return;
+		if (breakpoint_handler(regs))
+			return;
+		if (watchpoint_handler(regs))
+			return;
+		force_sig(SIGTRAP);
 #endif
-	force_sig(SIGTRAP);
-	exception_exit(prev_state);
+	}
+
+	irqentry_exit(regs, state);
 	return;
 }
 
-- 
2.36.0