On 2023-06-04 14:59:13+0200, Willy Tarreau wrote: > Hi Zhangjin, > > On Sun, Jun 04, 2023 at 01:34:29PM +0800, Zhangjin Wu wrote: > > most of the library routines share the same code model, let's add some > > macros to simplify the coding and shrink the code lines too. > > > > One added for syscall return, one added for syscall call, both of them > > can get the typeof 'return value' automatically. > > > > To get the return type of syscalls, __auto_type is better than typeof(), > > but it is not supported by the old compilers (before 2013, see [1]), so, > > use typeof() here. > > > > [1]: https://gcc.gnu.org/legacy-ml/gcc-patches/2013-11/msg01378.html > > > > Signed-off-by: Zhangjin Wu <falcon@xxxxxxxxxxx> > > --- > > tools/include/nolibc/sys.h | 15 +++++++++++++++ > > 1 file changed, 15 insertions(+) > > > > diff --git a/tools/include/nolibc/sys.h b/tools/include/nolibc/sys.h > > index 1d6f33f58629..937a8578e3d4 100644 > > --- a/tools/include/nolibc/sys.h > > +++ b/tools/include/nolibc/sys.h > > @@ -28,6 +28,21 @@ > > #include "errno.h" > > #include "types.h" > > > > +/* Syscall call and return helpers */ > > +#define __syscall_ret(ret) \ > > +({ \ > > + if (ret < 0) { \ > > + SET_ERRNO(-ret); \ > > + ret = (typeof(ret))-1; \ > > + } \ > > + ret; \ > > +}) > > + > > +#define __syscall(name, ...) \ > > +({ \ > > + typeof(sys_##name(__VA_ARGS__)) ret = sys_##name(__VA_ARGS__); \ > > + __syscall_ret(ret); \ > > +}) > > Well, I personally don't find that it increases legibility, on the > opposite. At first when reading the series, I thought you had dropped > errno setting on return. I think the reason is that when reading that > last macro, it's not at all obvious that __syscall_ret() is actually > modifying this ret value *and* returning it as the macro's result. > > If we'd want to go down that route, I suspect that something like this > would at least hint about what is being returned: > > +#define __syscall(name, ...) \ > +({ \ > + typeof(sys_##name(__VA_ARGS__)) ret = sys_##name(__VA_ARGS__); \ > + ret = __syscall_ret(ret); \ > +}) > > But I'm interested in others' opinion on this, particularly Thomas and > Arnd who review a significant number of patches. For now I prefer not > to take it before we've settled on a choice. While I see the value in factoring out this pattern I'm also not really happy with the implementation. Especially the magic delegation to "sys_##name". What about something like this: static inline long __ret_as_errno(long ret) /* or some other name */ { if (ret < 0) { SET_ERRNO(-ret); ret = -1; } return ret; } This avoids another macro by using a normal function. Syscall return values should always fit into long, at least extrapolating from syscall(2) and the fact that they are returned in registers. It would be a bit more verbose: int chdir(const char *path) { return __ret_as_errno(sys_chdir(path)); } But it's clear what's going on and also just one line. Thomas
