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)
- */
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@med.uni-goettingen.de * (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@AcuMS.aculab.c...
David
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)