> 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, Hi, Willy, I did add something like this in my local copy to pass the errno and retval arguments too: #define __syscall_ret3(ret, errno, retval) \ ({ \ if (ret < 0) { \ SET_ERRNO(errno); \ ret = (typeof(ret)retval; \ } \ ret; \ }) #define __syscall_ret(ret) __syscall_ret3(ret, -ret, -1) But when really using them, I found we could be able to set the ret as errno at first (and the reval is always -1 currently), then used the only simpler __syscall_ret() at last. > > 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); \ > > +}) > > It is clearer. > > 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. > It is reasonable, like it very much. > Syscall return values should always fit into long, at least > extra polating from syscall(2) and the fact that they are returned in > registers. Yes, I did use 'long' instead of 'int' for unistd.h locally, but since tried to let it work with 'void *' before (e.g. sys_brk, an older version support pass the errno value), so, the typeof() is used and the same to unistd.h, but at last, none of (void *) return type is really used in current patchset, so, we are able to use this normal function version without the checking of the type. > > 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. Thanks Thomas, It looks good and I do like the 'embedded' calling of sys_chrdir(path), but __syscall() looks cleaner and shorter too, let's put them together: int chdir(const char *path) { return __ret_as_errno(sys_chdir(path)); } int chdir(const char *path) { return __syscall(chdir, path); } And even with: int chdir(const char *path) { return __sysret(sys_chdir(path)); } __syscall() works likes syscall(), and the definition is similar to syscall(), but uses the syscall name instead of syscall number, If reserve __syscall(), the inline function would be renamed back to __syscall_ret() or something like the shorter __sysret(), to align with our new __syscall(). for sys.h: /* Syscall return helper, set errno as ret when ret < 0 */ static inline long __sysret(long ret) { if (ret < 0) { SET_ERRNO(-ret); ret = -1; } return ret; } /* Syscall call helper, use syscall name instead of syscall number */ #define __syscall(name, ...) __sysret(sys_##name(__VA_ARGS__)) for unistd.h: #define _syscall(N, ...) __sysret(my_syscall##N(__VA_ARGS__)) What about this version? The potential 'issue' may be mixing the use of __syscall(), _syscall() and syscall(), but the compilers may help to fix up this for us, I don't think it is a bottleneck. Best regards, Zhangjin > > Thomas
