From: Segher Boessenkool <segher@kernel.crashing.org>
To: Alexey Dobriyan <adobriyan@gmail.com>
Cc: akpm@linux-foundation.org, linux-arch@vger.kernel.org,
Catalin Marinas <catalin.marinas@arm.com>,
masahiroy@kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-kernel@vger.kernel.org, Paul Mackerras <paulus@samba.org>,
Will Deacon <will@kernel.org>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 3/3] isystem: delete global -isystem compile option
Date: Mon, 2 Aug 2021 11:47:47 -0500 [thread overview]
Message-ID: <20210802164747.GN1583@gate.crashing.org> (raw)
In-Reply-To: <YQeT5QRXc3CzK9nL@localhost.localdomain>
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?
> noreturn, alignas newest C standard
> are next.
What is wrong with <stdalign.h> and <stdnoreturn.h>?
> 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?
> > 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.
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.
Segher
next prev parent reply other threads:[~2021-08-02 16:55 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-01 20:13 [PATCH 1/3] isystem: trim/fixup stdarg.h and other headers Alexey Dobriyan
2021-08-01 20:13 ` [PATCH 2/3] isystem: ship and use stdarg.h Alexey Dobriyan
2021-08-03 7:14 ` Ard Biesheuvel
2021-08-17 1:30 ` Masahiro Yamada
2021-08-06 13:00 ` Rafael J. Wysocki
2021-08-01 20:13 ` [PATCH 3/3] isystem: delete global -isystem compile option Alexey Dobriyan
2021-08-01 21:32 ` Segher Boessenkool
2021-08-02 6:42 ` Alexey Dobriyan
2021-08-02 16:47 ` Segher Boessenkool [this message]
2021-08-02 20:30 ` Alexey Dobriyan
2021-08-02 21:42 ` Segher Boessenkool
2021-08-02 1:30 ` kernel test robot
2021-08-02 18:18 ` Nathan Chancellor
2021-08-02 20:32 ` Alexey Dobriyan
2021-08-02 20:38 ` Nathan Chancellor
2021-08-02 0:21 ` [PATCH 1/3] isystem: trim/fixup stdarg.h and other headers kernel test robot
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