Hi, David > From: Zhangjin Wu > > Sent: 07 August 2023 06:58 > ... > > +/* __auto_type is used instead of __typeof__ to workaround the build error > > + * 'error: assignment of read-only variable' when the argument has 'const' in > > + * the type, but __auto_type is a new feature from newer gcc version and it > > + * only works with 'const' from gcc 11.0 (__GXX_ABI_VERSION = 1016) > > + * https://gcc.gnu.org/legacy-ml/gcc-patches/2013-11/msg01378.html > > + */ > > You can use typeof((x) + 0) to lose the 'const' flag. > The only downside is that char/short become int. > Great, thanks! let's use it, and at least kill the branch using fixed 'long' type. #if __GXX_ABI_VERSION >= 1016 #define __typeofdecl(arg) __auto_type #else #define __typeofdecl(arg) __typeof__(arg) #endif #define __sysret(arg) \ ({ \ __typeofdecl((arg) + 0) __ret = (arg); \ if (__is_signed_type(__typeof__(arg))) { \ if ((long)__ret < 0) { \ SET_ERRNO(-(long)__ret); \ __ret = (__typeof__(arg))-1L; \ } \ } else { \ if ((unsigned long)__ret >= (unsigned long)-MAX_ERRNO) { \ SET_ERRNO(-(long)__ret); \ __ret = (__typeof__(arg))-1L; \ } \ } \ __ret; \ }) My simple test on nolibc-test shows David's typeof solution does give the same size result like __auto_type. what's your suggestion? simply give up the '__auto_type' stuff and use the generic __typeof__ version? Willy, could you please test David's typeof solution on the one which have 3-4% size inflating? or any other big programs using nolibc. > > + > > +#if __GXX_ABI_VERSION >= 1016 > > +#define __GXX_HAS_AUTO_TYPE_WITH_CONST_SUPPORT > > +#endif > > + > > +#ifdef __GXX_HAS_AUTO_TYPE_WITH_CONST_SUPPORT > > +#define __sysret(arg) \ > > +({ \ > > + __auto_type __ret = (arg); \ > > + if (__is_signed_type(__typeof__(arg))) { \ > > + if (__ret < 0) { \ > > + SET_ERRNO(-(long)__ret); \ > > + __ret = (__typeof__(arg))(-1L); \ > > + } \ > > + } else { \ > > + if ((unsigned long)__ret >= (unsigned long)-MAX_ERRNO) { \ > > + SET_ERRNO(-(long)__ret); \ > > + __ret = (__typeof__(arg))(-1L); \ > > + } \ > > + } \ > > + __ret; \ > > +}) > > + > > +#else /* ! __GXX_HAS_AUTO_TYPE_WITH_CONST_SUPPORT */ > > +#define __sysret(arg) \ > > +({ \ > > + long __ret = (long)(arg); \ > > + if (__is_signed_type(__typeof__(arg))) { \ > > + if (__ret < 0) { \ > > + SET_ERRNO(-__ret); \ > > + __ret = -1L; \ > > + } \ > > + } else { \ > > + if ((unsigned long)__ret >= (unsigned long)-MAX_ERRNO) { \ > > + SET_ERRNO(-__ret); \ > > + __ret = -1L; \ > > + } \ > > + } \ > > + (__typeof__(arg))__ret; \ > > +}) > > +#endif /* ! __GXX_HAS_AUTO_TYPE_WITH_CONST_SUPPORT */ > > with (retyped so it may be wrong): > #define is_constexpr(x) sizeof(*(0 ? (void *)((long)(x) * 0) : (int *)0)) == 1) > and (because even (void *)0 isn't completely constant): > #define is_pointer(x) (!is_constexpr((typeof(x))0)) > > You can probably do: > #define __sysret(arg) \ > ({ \ > typeof((arg) + 0) __ret = arg; \ > if (__built_choose_expr(is_pointer(arg), (unsigned long)-(MAX_ERRNO+1), __ret) \ > < (__built_choose_expr(is_pointer(arg), (unsigned long)__ret, 0)) { \ > SET_ERRNO(-__ret); \ > __reg = typeof(ret)-1L; \ > } \ > __ret; \ > }) > > Apart from the annoyance of having to reverse the conditional > that only has one copy of the check. > > Using two __builtin_choose_expr() saves you having to write two > comparisons that are valid for both pointer and integer. > It works perfectly. /* * This returns a constant expression while determining if an argument is * a constant expression, most importantly without evaluating the argument. * Glory to Martin Uecker <Martin.Uecker@xxxxxxxxxxxxxxxxxxxxx> * (from include/linux/const.h) */ #define __is_constexpr(x) \ (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8))) #define __is_pointer(x) (!__is_constexpr((__typeof__(x))0)) #define __sysret(arg) \ ({ \ __typeofdecl((arg) + 0) __ret = (arg); \ if (__builtin_choose_expr(__is_pointer(arg), (unsigned long)-(MAX_ERRNO + 1), ((long)__ret)) \ < __builtin_choose_expr(__is_pointer(arg), (unsigned long)__ret, 0)) { \ SET_ERRNO(-(long)__ret); \ __ret = (__typeof__(arg))-1L; \ } \ __ret; \ }) I have tried the 'is_constexpr()' macro but failed and didn't look into it, your explanation here [1] is very clear: You'll find that (void *)0 isn't 'constant enough' for is_constexpr() - so is_constexpr((type)0) can be used to detect pointer types. Best regards, Zhangjin --- [1]: https://lore.kernel.org/lkml/a1732bbffd1542d3b9dd34c92f45076c@xxxxxxxxxxxxxxxx/ > David > > - > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK > Registration No: 1397386 (Wales)
