On Mon, Aug 02, 2021 at 11:47:47AM -0500, Segher Boessenkool wrote: > On Mon, Aug 02, 2021 at 09:42:45AM +0300, Alexey Dobriyan wrote: > > On Sun, Aug 01, 2021 at 04:32:47PM -0500, Segher Boessenkool wrote: > > > On Sun, Aug 01, 2021 at 11:13:36PM +0300, Alexey Dobriyan wrote: > > > > In theory, it enables "leakage" of userspace headers into kernel which > > > > may present licensing problem. > > > > > > > -NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include) > > > > +NOSTDINC_FLAGS += -nostdinc > > > > > > This is removing the compiler's own include files. These are required > > > for all kinds of basic features, and required to be compliant to the C > > > standard at all. > > > > No they are not required. > > This is false, they *are* required, whenever you want to use these > features. If you do not include the required headers you get undefined > behaviour. > > > Kernel uses its own bool, uintptr_t and > > static_assert, memset(), CHAR_BIT. > > Yes, and it occasionally gets it wrong. Great fun. See c46bbf5d2def > for the latest episode in this saga. (Yes I know this is uapi so maybe > not the best example here, but it isn't like the kernel gets such things > wrong so often these days ;-) ) > > The kernel *cannot* make up its own types for this. It has to use the > types it is required to use (by C, by the ABIs, etc.) So why > reimplement this? Yes, it can. gcc headers have stuff like this: #define __PTRDIFF_TYPE__ long int #define __SIZE_TYPE__ long unsigned int If gcc can defined standard types, kernel can too. > > noreturn, alignas newest C standard > > are next. > > What is wrong with <stdalign.h> and <stdnoreturn.h>? These two are actually quite nice. Have you seen <stddef.h>? Loads of macrology crap. Kernel can ship nicer one. > > This version changelog didn't mention but kernel would use > > -ffreestanding too if not other problems with the flag. > > It is still true for freestanding C implementations, you just get a > severely reduced standard library, > > > > These are not "userspace headers", that is what > > > -nostdinc takes care of already. > > > > They are userspace headers in the sense they are external to the project > > just like userspace programs are external to the kernel. > > So you are going to rewrite all of the rest of GCC inside the kernel > project as well? What an argument. "the rest of GCC" is already there except for stdarg.h. > > > In the case of GCC all these headers are GPL-with-runtime-exception, so > > > claiming this can cause licensing problems is fearmongering. > > > > I agree licensing problem doesn't really exist. > > It would take gcc drop-in replacement with authors insane enough to not > > license standard headers properly. > > There does still not exist a drop-in replacement for GCC, not if you > look closely and/or rely on details (like the kernel does). Some of the > differences are hidden by "linux/compiler-*.h", but hardly all. > > > > I strongly advise against doing this. > > > > Kernel chose to be self-contained. > > That is largely historical, imo. Nowadays this is less necessary. I kind of agree as in kernel should use int8_t and stuff because they are standard. Also, -isystem removal disables <float.h> and <stdatomic.h> which is desireable. > Also, the kernel chose to *do* use the compiler include files. It is > you who wants to abolish that here. > > > -isystem removal makes sense then. > > -nostdinc -isystem $(shell $(CC) -print-file-name=include) makes sense > for that: you do indeed not want the userspace headers. Maiming the > compiler (by removing some of its functional parts, namely, its generic > headers) does not make sense. > > > It will be used for intrinsics where necessary. > > Like, everywhere. No, where necessary. Patch demostrates there are only a few places which want -isystem back.
