Re: [Qemu-devel] [PATCH 10/10] alpha-linux-user: Fix the getpriority syscall

[Peter Maydell]

On 25 July 2012 23:10, Richard Henderson <address@hidden> wrote:
> Alpha uses unbiased priority values in the syscall, with the a3
> return value signaling error conditions.  Therefore, properly
> interpret the libc getpriority as needed for the guest rather
> than passing the host value through unchanged.
>
> Signed-off-by: Richard Henderson <address@hidden>
> ---
>  linux-user/syscall.c |   20 +++++++++++++++-----
>  1 files changed, 15 insertions(+), 5 deletions(-)
>
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 2e1c1c0..b487635 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -218,7 +218,6 @@ _syscall3(int, sys_getdents, uint, fd, struct 
> linux_dirent *, dirp, uint, count)
>  #if defined(TARGET_NR_getdents64) && defined(__NR_getdents64)
>  _syscall3(int, sys_getdents64, uint, fd, struct linux_dirent64 *, dirp, 
> uint, count);
>  #endif
> -_syscall2(int, sys_getpriority, int, which, int, who);
>  #if defined(TARGET_NR__llseek) && defined(__NR_llseek)
>  _syscall5(int, _llseek,  uint,  fd, ulong, hi, ulong, lo,
>            loff_t *, res, uint, wh);
> @@ -6445,10 +6444,21 @@ abi_long do_syscall(void *cpu_env, int num, abi_long 
> arg1,
>          break;
>  #endif
>      case TARGET_NR_getpriority:
> -        /* libc does special remapping of the return value of
> -         * sys_getpriority() so it's just easiest to call
> -         * sys_getpriority() directly rather than through libc. */
> -        ret = get_errno(sys_getpriority(arg1, arg2));
> +        /* Note that negative values are valid for getpriority, so we must
> +           differentiate based on errno settings.  */
> +        errno = 0;
> +        ret = getpriority(arg1, arg2);
> +        if (ret == -1 && errno != 0) {
> +            ret = get_errno(errno);
> +            break;
> +        }
> +#ifdef TARGET_ALPHA
> +        /* Return value is the unbiased priority.  Signal no error.  */
> +        ((CPUAlphaState *)cpu_env)->ir[IR_V0] = 0;

Having do_syscall fish around in the cpu register struct seems a
bit ugly, but we do it elsewhere so I guess this is OK.

> +#else
> +        /* Return value is a biased priority to avoid negative numbers.  */
> +        ret = 20 - ret;
> +#endif
>          break;
>      case TARGET_NR_setpriority:
>          ret = get_errno(setpriority(arg1, arg2, arg3));

Sanity check -- it is only getpriority that has the biasing, not
setpriority?

-- PMM