Re: [PATCH v12 2/7] linux: Introduce INTERNAL_VSYSCALL

[Florian Weimer <fw@deneb.enyo.de>]

* Evan Green:

> It's kinda awkward without the label because the regular syscall is
> made either if vdsop is NULL or returns ENOSYS (which is two checks on
> the return value, so doesn't lend itself to inlining in the if
> statement). The best I could come up with without the label is to
> duplicate the syscall_call:
>
> #define INTERNAL_VSYSCALL(name, nr, args...)                      \
>   ({                                          \
>     long int sc_ret;                                  \
>                                           \
>     __typeof (GLRO(dl_vdso_##name)) vdsop = GLRO(dl_vdso_##name);          \
>     if (vdsop != NULL)                                  \
>       {                                          \
>     sc_ret = INTERNAL_VSYSCALL_CALL (vdsop, nr, ##args);              \
>     if ((INTERNAL_SYSCALL_ERROR_P (sc_ret)) &&                  \
>         (INTERNAL_SYSCALL_ERRNO (sc_ret) == ENOSYS))              \
>       sc_ret = INTERNAL_SYSCALL_CALL (name, ##args);              \
>       }                                          \
>     else                                      \
>       {                                          \
>     sc_ret = INTERNAL_SYSCALL_CALL (name, ##args);                  \
>       }                                          \
>     sc_ret;                                      \
>   })

Indentation is off for me, for clarification:

#define INTERNAL_VSYSCALL(name, nr, args...)                            \
  ({                                                                    \
    long int sc_ret;                                                    \
                                                                        \
    __typeof (GLRO(dl_vdso_##name)) vdsop = GLRO(dl_vdso_##name);       \
    if (vdsop != NULL)                                                  \
      {                                                                 \
        sc_ret = INTERNAL_VSYSCALL_CALL (vdsop, nr, ##args);            \
        if ((INTERNAL_SYSCALL_ERROR_P (sc_ret)) &&                      \
            (INTERNAL_SYSCALL_ERRNO (sc_ret) == ENOSYS))                \
          sc_ret = INTERNAL_SYSCALL_CALL (name, ##args);                \
      }                                                                 \
    else                                                                \
      {                                                                 \
        sc_ret = INTERNAL_SYSCALL_CALL (name, ##args);                  \
      }                                                                 \
    sc_ret;                                                             \
  })

?: does not work because the comparison with -ENOSYS discards the
return value.

Does this look correct?

#define INTERNAL_VSYSCALL(name, nr, args...)                            \
  ({                                                                    \
    long int sc_ret = -ENOSYS;                                          \
    __typeof (GLRO(dl_vdso_##name)) vdsop = GLRO(dl_vdso_##name);       \
    if (vdsop != NULL)                                                  \
      sc_ret = INTERNAL_VSYSCALL_CALL (vdsop, nr, ##args);              \
    if (sc_ret == -ENOSYS)                                              \
      sc_ret = INTERNAL_SYSCALL_CALL (name, ##args);                    \
    sc_ret;                                                             \
  })

I expect GCC to generate decent code for it.