[PATCH] riscv: ptrace: add argn syntax

[Jeff Xie]

This enables ftrace kprobe events to access kernel function
arguments via $argN syntax.

Signed-off-by: Jeff Xie <huan.xie@xxxxxxxx>
---
 arch/riscv/Kconfig              |  1 +
 arch/riscv/include/asm/ptrace.h | 31 +++++++++++++++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 18ec0f9bb8d5..f9246a7d0a31 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -88,6 +88,7 @@ config RISCV
 	select HAVE_PERF_REGS
 	select HAVE_PERF_USER_STACK_DUMP
 	select HAVE_REGS_AND_STACK_ACCESS_API
+	select HAVE_FUNCTION_ARG_ACCESS_API
 	select HAVE_STACKPROTECTOR
 	select HAVE_SYSCALL_TRACEPOINTS
 	select IRQ_DOMAIN
diff --git a/arch/riscv/include/asm/ptrace.h b/arch/riscv/include/asm/ptrace.h
index 09ad4e923510..fdb59ee405ee 100644
--- a/arch/riscv/include/asm/ptrace.h
+++ b/arch/riscv/include/asm/ptrace.h
@@ -141,6 +141,37 @@ static inline unsigned long regs_get_register(struct pt_regs *regs,
 
 	return *(unsigned long *)((unsigned long)regs + offset);
 }
+
+/**
+ * regs_get_kernel_argument() - get Nth function argument in kernel
+ * @regs:       pt_regs of that context
+ * @n:          function argument number (start from 0)
+ *
+ * regs_get_argument() returns @n th argument of the function call.
+ *
+ * Note you can get the parameter correctly if the function has no
+ * more than eight arguments.
+ */
+static inline unsigned long regs_get_kernel_argument(struct pt_regs *regs,
+						unsigned int n)
+{
+#define NR_REG_ARGUMENTS 8
+	static const unsigned int argument_offs[] = {
+		offsetof(struct pt_regs, a0),
+		offsetof(struct pt_regs, a1),
+		offsetof(struct pt_regs, a2),
+		offsetof(struct pt_regs, a3),
+		offsetof(struct pt_regs, a4),
+		offsetof(struct pt_regs, a5),
+		offsetof(struct pt_regs, a6),
+		offsetof(struct pt_regs, a7),
+	};
+
+	if (n < NR_REG_ARGUMENTS)
+		return regs_get_register(regs, argument_offs[n]);
+	return 0;
+}
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* _ASM_RISCV_PTRACE_H */
-- 
2.26.2