Am Dienstag, dem 19.12.2023 um 12:20 -0500 schrieb Jason Merrill: > On 12/19/23 03:47, Jakub Jelinek wrote: > > On Tue, Dec 19, 2023 at 08:11:11AM +0100, Martin Uecker wrote: > > > Am Montag, dem 18.12.2023 um 20:14 +0100 schrieb Jakub Jelinek: > > > > Hi! > > > > > > > > The following patch changes -Walloc-size warning to no longer warn > > > > about int *p = calloc (1, sizeof (int));, because as discussed earlier, > > > > the size is IMNSHO sufficient in that case, for alloc_size with 2 > > > > arguments warns if the product of the 2 arguments is insufficiently > > > > small. > > > > > > > > Also, it warns also for explicit casts of malloc/calloc etc. calls > > > > rather than just implicit, so not just > > > > int *p = malloc (1); > > > > but also > > > > int *p = (int *) malloc (1); > > > > > > > > It also fixes some ICEs where the code didn't verify the alloc_size > > > > arguments properly (Walloc-size-5.c testcase ICEs with vanilla trunk). > > > > > > > > And lastly, it introduces a coding style warning, > > > > -Wcalloc-transposed-args > > > > to warn for calloc (sizeof (struct S), 1) and similar calls (regardless > > > > of what they are cast to, warning whenever first argument is sizeof and > > > > the second is not). > > > > > > I would generally see function arguments that are swapped relative > > > to the documented ABI as more than a coding style issue even in > > > cases where it can be expected to make no difference. > > > > If you have suggestions how to reword the documentation, would that be > > sufficient for you? I still don't see why given correct alignment one can't > > store struct S into sizeof (struct S) sized heap char array, > > Seems to me one can in C++, anyway. An unsigned char array can provide > storage for another type, and the call to calloc can be interpreted as > creating such an array if that gives the program defined behavior. > https://eel.is/c++draft/intro.object#def:provides_storage > https://eel.is/c++draft/intro.object#def:object,implicit_creation
This is also true in C. There is nothing wrong with calloc(10, 1) allocating a char array with 10 elements and then storing a struct of size 10 in it. Martin >
