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>

4 files changed, 46 insertions, 0 deletions

diff --git a/arch/loongarch/include/asm/inst.h b/arch/loongarch/include/asm/inst.h
index 7eedd83fd0d7..36cc5eb4f852 100644
--- a/arch/loongarch/include/asm/inst.h
+++ b/arch/loongarch/include/asm/inst.h
@@ -351,6 +351,44 @@ static inline bool is_stack_alloc_ins(union loongarch_instruction *ip)
 		is_imm12_negative(ip->reg2i12_format.immediate);
 }
 
+static inline bool is_self_loop_ins(union loongarch_instruction *ip, struct pt_regs *regs)
+{
+	switch (ip->reg0i26_format.opcode) {
+	case b_op:
+	case bl_op:
+		if (ip->reg0i26_format.immediate_l == 0
+		    && ip->reg0i26_format.immediate_h == 0)
+			return true;
+	}
+
+	switch (ip->reg1i21_format.opcode) {
+	case beqz_op:
+	case bnez_op:
+	case bceqz_op:
+		if (ip->reg1i21_format.immediate_l == 0
+		    && ip->reg1i21_format.immediate_h == 0)
+			return true;
+	}
+
+	switch (ip->reg2i16_format.opcode) {
+	case beq_op:
+	case bne_op:
+	case blt_op:
+	case bge_op:
+	case bltu_op:
+	case bgeu_op:
+		if (ip->reg2i16_format.immediate == 0)
+			return true;
+		break;
+	case jirl_op:
+		if (regs->regs[ip->reg2i16_format.rj] +
+		    ((unsigned long)ip->reg2i16_format.immediate << 2) == (unsigned long)ip)
+			return true;
+	}
+
+	return false;
+}
+
 int larch_insn_read(void *addr, u32 *insnp);
 int larch_insn_write(void *addr, u32 insn);
 int larch_insn_patch_text(void *addr, u32 insn);
diff --git a/arch/loongarch/include/asm/loongarch.h b/arch/loongarch/include/asm/loongarch.h
index e9aed583a064..65b7dcdea16d 100644
--- a/arch/loongarch/include/asm/loongarch.h
+++ b/arch/loongarch/include/asm/loongarch.h
@@ -1055,6 +1055,9 @@ static __always_inline void iocsr_write64(u64 val, u32 reg)
 #define LOONGARCH_CSR_DERA		0x501	/* debug era */
 #define LOONGARCH_CSR_DESAVE		0x502	/* debug save */
 
+#define CSR_FWPC_SKIP_SHIFT		16
+#define CSR_FWPC_SKIP			(_ULCAST_(1) << CSR_FWPC_SKIP_SHIFT)
+
 /*
  * CSR_ECFG IM
  */
diff --git a/arch/loongarch/include/asm/processor.h b/arch/loongarch/include/asm/processor.h
index 5edf78c3a5b4..636e1c66398c 100644
--- a/arch/loongarch/include/asm/processor.h
+++ b/arch/loongarch/include/asm/processor.h
@@ -125,6 +125,7 @@ struct thread_struct {
 	/* Other stuff associated with the thread. */
 	unsigned long trap_nr;
 	unsigned long error_code;
+	unsigned long single_step; /* Used by PTRACE_SINGLESTEP */
 	struct loongarch_vdso_info *vdso;
 
 	/*
diff --git a/arch/loongarch/include/asm/ptrace.h b/arch/loongarch/include/asm/ptrace.h
index 5d3872131866..6eab4393b108 100644
--- a/arch/loongarch/include/asm/ptrace.h
+++ b/arch/loongarch/include/asm/ptrace.h
@@ -183,4 +183,8 @@ static inline void user_stack_pointer_set(struct pt_regs *regs,
 	regs->regs[3] = val;
 }
 
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+#define arch_has_single_step()		(1)
+#endif
+
 #endif /* _ASM_PTRACE_H */