> From: Bruce Richardson [mailto:[email protected]] > Sent: Monday, 12 January 2026 10.14 > > On Sun, Jan 11, 2026 at 07:59:19AM -0800, Stephen Hemminger wrote: > > On Sun, 11 Jan 2026 10:00:32 -0500 > > [email protected] wrote: > > > > > +#define RTE_PTR_ADD(ptr, x) \ > > > + (__extension__ ({ \ > > > + /* Diagnostics suppressed for internal macro operations > only. \ > > > + * Compiler type-checks all _Generic branches even when > unselected, \ > > > + * triggering warnings with no external impact. */ \ > > > + __rte_diagnostic_push \ > > > + __rte_diagnostic_ignored_wcast_qual \ > > > + _Pragma("GCC diagnostic ignored \"-Wconditional-type- > mismatch\"") \ > > > + /* Uses uintptr_t arithmetic for integer types (API > compatibility), \ > > > + * and char* arithmetic for pointer types (enables > optimization). */ \ > > > + __auto_type _ptr_result = _Generic((ptr), \ > > > + unsigned long long: ((void *)((uintptr_t)(ptr) + > (x))), \ > > > + long long: ((void *)((uintptr_t)(ptr) + > (x))), \ > > > + unsigned long: ((void *)((uintptr_t)(ptr) + > (x))), \ > > > + long: ((void *)((uintptr_t)(ptr) + > (x))), \ > > > + unsigned int: ((void *)((uintptr_t)(ptr) + > (x))), \ > > > + int: ((void *)((uintptr_t)(ptr) + > (x))), \ > > > + unsigned short: ((void *)((uintptr_t)(ptr) + > (x))), \ > > > + short: ((void *)((uintptr_t)(ptr) + > (x))), \ > > > + unsigned char: ((void *)((uintptr_t)(ptr) + > (x))), \ > > > + signed char: ((void *)((uintptr_t)(ptr) + > (x))), \ > > > + char: ((void *)((uintptr_t)(ptr) + > (x))), \ > > > + _Bool: ((void *)((uintptr_t)(ptr) + > (x))), \ > > > + /* Ternary with null pointer constant: per C11, if > one operand \ > > > + * is a null pointer constant and the other is a > pointer, the \ > > > + * result type is qualified per the pointer operand, > normalizing \ > > > + * const T* to const void* and T* to void*. */ \ > > > + default: _Generic((1 ? (ptr) : (void *)0), \ > > > + const void *: ((void *)((const char *)(ptr) + > (x))), \ > > > + default: ((void *)((char *)(ptr) + (x))) \ > > > + ) \ > > > + ); \ > > > + __rte_diagnostic_pop \ > > > + _ptr_result; \ > > > + })) > > > > Good idea in general but the macro is way to big and therefore hard > to read. > > The comments could be outside the macro. > > > > Any code that adds dependency on a pragma to work is brittle and > likely > > to allow bugs through. Please figure out how to do it without. > > Do we need to handle the case of users calling RTE_PTR_ADD with integer > values? Using this macro to essentially cast an integer to pointer > seems > strange. Even if it's occasionally used, I think keeping things simple > and > just globally changing to use "char *" is a better approach. > > The only case where I'd consider trying to keep compatibility using > uintptr_t is if the pointer parameter is a volatile one. Even then, we > can > probably handle that as with the "const" modifier, right?
None of the RTE_PTR_ macros can handle qualifiers (const, volatile). Maybe it would be better to provide a new set of macros with a qualifier parameter, instead of adding new macros with e.g. _CONST in the names.
