Re: [PATCH v2 2/3] riscv: Add hwprobe vdso call support

[Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>]

On 21/02/23 16:15, Evan Green wrote:
> The new riscv_hwprobe syscall also comes with a vDSO for faster answers
> to your most common questions. Call in today to speak with a kernel
> representative near you!
> 
> Signed-off-by: Evan Green <evan@rivosinc.com>
> ---
> 
> Changes in v2:
>  - Add vDSO interface
> 
>  sysdeps/unix/sysv/linux/dl-vdso-setup.c | 10 ++++++++++
>  sysdeps/unix/sysv/linux/dl-vdso-setup.h |  3 +++
>  sysdeps/unix/sysv/linux/riscv/hwprobe.c |  6 ++++++
>  sysdeps/unix/sysv/linux/riscv/sysdep.h  |  1 +
>  4 files changed, 20 insertions(+)
> 
> diff --git a/sysdeps/unix/sysv/linux/dl-vdso-setup.c b/sysdeps/unix/sysv/linux/dl-vdso-setup.c
> index 68fa8de641..3fe304a0c7 100644
> --- a/sysdeps/unix/sysv/linux/dl-vdso-setup.c
> +++ b/sysdeps/unix/sysv/linux/dl-vdso-setup.c
> @@ -71,6 +71,16 @@ PROCINFO_CLASS int (*_dl_vdso_clock_getres_time64) (clockid_t,
>  # ifdef HAVE_GET_TBFREQ
>  PROCINFO_CLASS uint64_t (*_dl_vdso_get_tbfreq)(void) RELRO;
>  # endif
> +
> +/* RISC-V specific ones.  */
> +# ifdef HAVE_RISCV_HWPROBE
> +PROCINFO_CLASS int (*_dl_vdso_riscv_hwprobe)(void *,
> +                                             long,
> +                                             long,
> +                                             unsigned long *,
> +                                             long) RELRO;
> +# endif
> +
>  #endif
>  
>  #undef RELRO
> diff --git a/sysdeps/unix/sysv/linux/dl-vdso-setup.h b/sysdeps/unix/sysv/linux/dl-vdso-setup.h
> index 867072b897..39eafd5316 100644
> --- a/sysdeps/unix/sysv/linux/dl-vdso-setup.h
> +++ b/sysdeps/unix/sysv/linux/dl-vdso-setup.h
> @@ -47,6 +47,9 @@ setup_vdso_pointers (void)
>  #ifdef HAVE_GET_TBFREQ
>    GLRO(dl_vdso_get_tbfreq) = dl_vdso_vsym (HAVE_GET_TBFREQ);
>  #endif
> +#ifdef HAVE_RISCV_HWPROBE
> +  GLRO(dl_vdso_riscv_hwprobe) = dl_vdso_vsym (HAVE_RISCV_HWPROBE);
> +#endif
>  }
>  
>  #endif
> diff --git a/sysdeps/unix/sysv/linux/riscv/hwprobe.c b/sysdeps/unix/sysv/linux/riscv/hwprobe.c
> index 74f68889ca..2c61a67db7 100644
> --- a/sysdeps/unix/sysv/linux/riscv/hwprobe.c
> +++ b/sysdeps/unix/sysv/linux/riscv/hwprobe.c
> @@ -20,11 +20,17 @@
>  #include <sys/syscall.h>
>  #include <sys/hwprobe.h>
>  #include <sysdep.h>
> +#include <sysdep-vdso.h>
>  
>  int
>  __riscv_hwprobe (struct riscv_hwprobe *pairs, long pair_count,
>    long cpu_count, unsigned long *cpus, unsigned long flags)
>  {
> + /* The vDSO may be able to provide the answer without a syscall. */
> +#ifdef HAVE_RISCV_HWPROBE
> +  INLINE_VSYSCALL(riscv_hwprobe, 5, pairs, pair_count, cpu_count, cpus, flags);
> +#else
>    return INLINE_SYSCALL_CALL (riscv_hwprobe, pairs, pair_count,
>                           cpu_count, cpus, flags);
> +#endif
>  }

The HAVE_RISCV_HWPROBE is always defined for RISCV, so there is no need
to use the fallback (INLINE_VSYSCALL already issues the syscall if the
dl_vdso_get_tbfreq is NULL). 

> diff --git a/sysdeps/unix/sysv/linux/riscv/sysdep.h b/sysdeps/unix/sysv/linux/riscv/sysdep.h
> index 4af5fe5dbc..ba17aaaff2 100644
> --- a/sysdeps/unix/sysv/linux/riscv/sysdep.h
> +++ b/sysdeps/unix/sysv/linux/riscv/sysdep.h
> @@ -155,6 +155,7 @@
>  /* List of system calls which are supported as vsyscalls (for RV32 and
>     RV64).  */
>  # define HAVE_GETCPU_VSYSCALL		"__vdso_getcpu"
> +# define HAVE_RISCV_HWPROBE		"__vdso_riscv_hwprobe"
>  
>  # undef HAVE_INTERNAL_BRK_ADDR_SYMBOL
>  # define HAVE_INTERNAL_BRK_ADDR_SYMBOL 1