linux-kernel - Re: [GIT PULL] compiler-attributes for v5.3-rc8

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Date:   Thu, 5 Sep 2019 10:18:41 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Will Deacon <will@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        "David S. Miller" <davem@...emloft.net>,
        Paul Burton <paul.burton@...s.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] compiler-attributes for v5.3-rc8

On Thu, Sep 5, 2019 at 9:20 AM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Wed, Sep 4, 2019 at 11:18 AM Miguel Ojeda
> <miguel.ojeda.sandonis@...il.com> wrote:
> >
> > I was going to send this for 5.4 since it is not that trivial, but since
> > you are doing an -rc8, and it fixes an oops, please consider pulling it.
>
> I looked at this, and while it seems safe, I end up worrying.
>
> Macro stringification isn't entirely obvious, and an unquoted string
> could become corrupted if the stringification ends up not happening
> immediately.
>
> It does seem safe just because we do
>
>   #define __section(S)   __attribute__((__section__(#S)))
>
> but I had to go _check_ that we do, because it wouldn't have been safe
> if there had been another level of macro expansion, because then the
> argument in turn could have been expanded before it was stringified.
>
> So sometimes you actually _want_ to pass in a string to be
> stringified, because it's safer. I realize it then gets string-quoted,
> but this has worked for gcc. Even if I suspect nobody really _thought_
> about it.
>
> So I'm not unhappy about the patch, but it's the kind of thing I'd
> really prefer not to do at this stage.
>
> Particularly since it seems to do other things too than just fix
> double quoting. As far as I can tell, it doesn't just fix double
> string quoting, it changes a lot of singly-quoted strings to use the
> macro and unquotes them, ie
>
>   - __attribute__((__section__(".arch.info.init"))) = {   \
>   + __section(.arch.info.init) = {        \
>
> doesn't actually "fix" anything that I can see, it just uses the simpler form.

Please consider picking up just:
https://github.com/ojeda/linux/commit/c97e82b97f4bba00304905fe7965f923abd2d755
That lone patch is the one that fixes the particularly observed Oops.
The rest are just cleanup; if I made that change in the more important
patch, why not clean up the rest of the instances in the kernel?
-- 
Thanks,
~Nick Desaulniers