linux-kernel - Re: [PATCH 2/8] kbuild: prevent exported headers from including <stdlib.h>, <stdbool.h>

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Date:   Mon, 4 Apr 2022 10:01:49 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 2/8] kbuild: prevent exported headers from including
 <stdlib.h>, <stdbool.h>

On Mon, Apr 4, 2022 at 9:41 AM Christoph Hellwig <hch@...radead.org> wrote:
>
> On Mon, Apr 04, 2022 at 03:19:42PM +0900, Masahiro Yamada wrote:
> > If we can make kernel headers self-contained (that is, none of exported
> > kernel headers includes system headers), we will be able to add the
> > -nostdinc flag, but that is much far from where we stand now.
>
> What is still missing for that?

One case that I don't know how to solve is

include/uapi/sound/asound.h:typedef struct { unsigned char
pad[sizeof(time_t) - sizeof(int)]; } __time_pad;

Here we define a structure layout based on a libc-provided type. There are two
possible variants (32-bit and 64-bit time_t), and the kernel interface
can handle
both versions because they get different ioctl command numbers, but user space
must see the one that matches its normal time_t.

There are a couple of similar cases like this, but I think the other ones don't
need to define architecture specific padding like this.

       Arnd