Re: [PATCH] linux-user: Implement faccessat2

[Laurent Vivier <laurent@vivier.eu>]

Le 09/10/2022 à 08:08, WANG Xuerui a écrit :
> User space has been preferring this syscall for a while, due to its
> closer match with C semantics, and newer platforms such as LoongArch
> apparently have libc implementations that don't fallback to faccessat
> so normal access checks are failing without the emulation in place.
> 
> Tested by successfully emerging several packages within a Gentoo loong
> stage3 chroot, emulated on amd64 with help of static qemu-loongarch64.
> 
> Reported-by: Andreas K. Hüttel <dilfridge@gentoo.org>
> Signed-off-by: WANG Xuerui <xen0n@gentoo.org>
> ---
>   linux-user/strace.list | 3 +++
>   linux-user/syscall.c   | 9 +++++++++
>   2 files changed, 12 insertions(+)
> 
> diff --git a/linux-user/strace.list b/linux-user/strace.list
> index a87415bf3d..3df2184580 100644
> --- a/linux-user/strace.list
> +++ b/linux-user/strace.list
> @@ -178,6 +178,9 @@
>   #ifdef TARGET_NR_faccessat
>   { TARGET_NR_faccessat, "faccessat" , NULL, print_faccessat, NULL },
>   #endif
> +#ifdef TARGET_NR_faccessat2
> +{ TARGET_NR_faccessat2, "faccessat2" , NULL, print_faccessat, NULL },
> +#endif
>   #ifdef TARGET_NR_fadvise64
>   { TARGET_NR_fadvise64, "fadvise64" , NULL, NULL, NULL },
>   #endif
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 2e954d8dbd..a81f0b65b9 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -9110,6 +9110,15 @@ static abi_long do_syscall1(CPUArchState *cpu_env, int num, abi_long arg1,
>           unlock_user(p, arg2, 0);
>           return ret;
>   #endif
> +#if defined(TARGET_NR_faccessat2) && defined(__NR_faccessat2)
> +    case TARGET_NR_faccessat2:
> +        if (!(p = lock_user_string(arg2))) {
> +            return -TARGET_EFAULT;
> +        }
> +        ret = get_errno(faccessat(arg1, p, arg3, arg4));
> +        unlock_user(p, arg2, 0);
> +        return ret;
> +#endif
>   #ifdef TARGET_NR_nice /* not on alpha */
>       case TARGET_NR_nice:
>           return get_errno(nice(arg1));

I have applied this patch to my linux-user-for-7.2 branch,
adding defined(TARGET_NR_faccessat2) for print_faccessat() and removing the defined(__NR_faccessat2) 
in syscall.c (as we call the glibc wrapper).

Thanks,
Laurent