[PATCH -fixes] riscv: Fix ftrace syscall handling which are now prefixed with __riscv_

[Alexandre Ghiti]

@Conor Dooley This fails checkpatch but the documentation here states
that this is how to do:
https://elixir.bootlin.com/linux/latest/source/Documentation/trace/ftrace-design.rst#L246

On Tue, Oct 3, 2023 at 8:24 PM Alexandre Ghiti <alexghiti at rivosinc.com> wrote:
>
> ftrace creates entries for each syscall in the tracefs but has failed
> since commit 08d0ce30e0e4 ("riscv: Implement syscall wrappers") which
> prefixes all riscv syscalls with __riscv_.
>
> So fix this by implementing arch_syscall_match_sym_name() which allows us
> to ignore this prefix.
>
> And also ignore compat syscalls like x86/arm64 by implementing
> arch_trace_is_compat_syscall().
>
> Fixes: 08d0ce30e0e4 ("riscv: Implement syscall wrappers")
> Signed-off-by: Alexandre Ghiti <alexghiti at rivosinc.com>
> ---
>  arch/riscv/include/asm/ftrace.h | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
>
> diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
> index 740a979171e5..2b2f5df7ef2c 100644
> --- a/arch/riscv/include/asm/ftrace.h
> +++ b/arch/riscv/include/asm/ftrace.h
> @@ -31,6 +31,27 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)
>         return addr;
>  }
>
> +/*
> + * Let's do like x86/arm64 and ignore the compat syscalls.
> + */
> +#define ARCH_TRACE_IGNORE_COMPAT_SYSCALLS
> +static inline bool arch_trace_is_compat_syscall(struct pt_regs *regs)
> +{
> +       return is_compat_task();
> +}
> +
> +#define ARCH_HAS_SYSCALL_MATCH_SYM_NAME
> +static inline bool arch_syscall_match_sym_name(const char *sym,
> +                                              const char *name)
> +{
> +       /*
> +        * Since all syscall functions have __riscv_ prefix, we must skip it.
> +        * However, as we described above, we decided to ignore compat
> +        * syscalls, so we don't care about __riscv_compat_ prefix here.
> +        */
> +       return !strcmp(sym + 8, name);
> +}
> +
>  struct dyn_arch_ftrace {
>  };
>  #endif
> --
> 2.39.2
>