2021-06-20 12:04:36

by Jeff Xie

Subject: [PATCH] riscv: ptrace: add argn syntax

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

Signed-off-by: Jeff Xie <[email protected]>
---
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

2021-07-06 19:12:09

by Palmer Dabbelt

Subject: Re: [PATCH] riscv: ptrace: add argn syntax

On Sun, 20 Jun 2021 05:01:51 PDT (-0700), [email protected] wrote:
> This enables ftrace kprobe events to access kernel function
> arguments via $argN syntax.
>
> Signed-off-by: Jeff Xie <[email protected]>
> ---
> 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 */

This is on for-next. I cleaned it up a bit to avoid leaking that
#define.