Re: [PATCH v2] riscv: add CALLER_ADDRx support

[Zong Li]

On Fri, Feb 2, 2024 at 9:51 AM Zong Li <zong.li@xxxxxxxxxx> wrote:
>
> CALLER_ADDRx returns caller's address at specified level, they are used
> for several tracers. These macros eventually use
> __builtin_return_address(n) to get the caller's address if arch doesn't
> define their own implementation.
>
> In RISC-V, __builtin_return_address(n) only works when n == 0, we need
> to walk the stack frame to get the caller's address at specified level.
>
> data.level started from 'level + 3' due to the call flow of getting
> caller's address in RISC-V implementation. If we don't have additional
> three iteration, the level is corresponding to follows:
>
> callsite -> return_address -> arch_stack_walk -> walk_stackframe
> |           |                 |                  |
> level 3     level 2           level 1            level 0
>
> Fixes: 10626c32e382 ("riscv/ftrace: Add basic support")
>
> Reviewed-by: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx>
> Signed-off-by: Zong Li <zong.li@xxxxxxxxxx>
> ---
>
> Changed in v2:
> - Rebase to v6.8-rc2
> - Add noinline attribute for return_address()
> - Add a fixes tag
>
>  arch/riscv/include/asm/ftrace.h    |  5 ++++
>  arch/riscv/kernel/Makefile         |  2 ++
>  arch/riscv/kernel/return_address.c | 48 ++++++++++++++++++++++++++++++
>  3 files changed, 55 insertions(+)
>  create mode 100644 arch/riscv/kernel/return_address.c
>
> diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
> index 329172122952..15055f9df4da 100644
> --- a/arch/riscv/include/asm/ftrace.h
> +++ b/arch/riscv/include/asm/ftrace.h
> @@ -25,6 +25,11 @@
>
>  #define ARCH_SUPPORTS_FTRACE_OPS 1
>  #ifndef __ASSEMBLY__
> +
> +extern void *return_address(unsigned int level);
> +
> +#define ftrace_return_address(n) return_address(n)
> +
>  void MCOUNT_NAME(void);
>  static inline unsigned long ftrace_call_adjust(unsigned long addr)
>  {
> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> index f71910718053..604d6bf7e476 100644
> --- a/arch/riscv/kernel/Makefile
> +++ b/arch/riscv/kernel/Makefile
> @@ -7,6 +7,7 @@ ifdef CONFIG_FTRACE
>  CFLAGS_REMOVE_ftrace.o = $(CC_FLAGS_FTRACE)
>  CFLAGS_REMOVE_patch.o  = $(CC_FLAGS_FTRACE)
>  CFLAGS_REMOVE_sbi.o    = $(CC_FLAGS_FTRACE)
> +CFLAGS_REMOVE_return_address.o = $(CC_FLAGS_FTRACE)
>  endif
>  CFLAGS_syscall_table.o += $(call cc-option,-Wno-override-init,)
>  CFLAGS_compat_syscall_table.o += $(call cc-option,-Wno-override-init,)
> @@ -46,6 +47,7 @@ obj-y += irq.o
>  obj-y  += process.o
>  obj-y  += ptrace.o
>  obj-y  += reset.o
> +obj-y  += return_address.o
>  obj-y  += setup.o
>  obj-y  += signal.o
>  obj-y  += syscall_table.o
> diff --git a/arch/riscv/kernel/return_address.c b/arch/riscv/kernel/return_address.c
> new file mode 100644
> index 000000000000..c8115ec8fb30
> --- /dev/null
> +++ b/arch/riscv/kernel/return_address.c
> @@ -0,0 +1,48 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * This code come from arch/arm64/kernel/return_address.c
> + *
> + * Copyright (C) 2023 SiFive.
> + */
> +
> +#include <linux/export.h>
> +#include <linux/kprobes.h>
> +#include <linux/stacktrace.h>
> +
> +struct return_address_data {
> +       unsigned int level;
> +       void *addr;
> +};
> +
> +static bool save_return_addr(void *d, unsigned long pc)
> +{
> +       struct return_address_data *data = d;
> +
> +       if (!data->level) {
> +               data->addr = (void *)pc;
> +               return false;
> +       }
> +
> +       --data->level;
> +
> +       return true;
> +}
> +NOKPROBE_SYMBOL(save_return_addr);
> +
> +noinline void *return_address(unsigned int level)
> +{
> +       struct return_address_data data;
> +
> +       data.level = level + 3;
> +       data.addr = NULL;
> +
> +       arch_stack_walk(save_return_addr, &data, current, NULL);
> +
> +       if (!data.level)
> +               return data.addr;
> +       else
> +               return NULL;
> +
> +}
> +EXPORT_SYMBOL_GPL(return_address);
> +NOKPROBE_SYMBOL(return_address);
> --
> 2.17.1
>

Hi all,
Is there anything that can be improved in this patch? Thanks.