From: Michael Ellerman <mpe@ellerman•id.au>
To: Geert Uytterhoeven <geert@linux-m68k•org>,
Segher Boessenkool <segher@kernel•crashing.org>
Cc: Arnd Bergmann <arnd@arndb•de>, Geoff Levand <geoff@infradead•org>,
Linux Kernel Mailing List <linux-kernel@vger•kernel.org>,
clang-built-linux <clang-built-linux@googlegroups•com>,
Paul Mackerras <paulus@samba•org>, Joel Stanley <joel@jms•id.au>,
Nathan Chancellor <natechancellor@gmail•com>,
linuxppc-dev <linuxppc-dev@lists•ozlabs.org>
Subject: Re: [PATCH] powerpc/boot: Use address-of operator on section symbols
Date: Mon, 03 Aug 2020 21:09:36 +1000 [thread overview]
Message-ID: <87zh7cyoi7.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <CAMuHMdUmHE-KVQuo=b2rn9EPgmnqSDi4i16NPbL5rXLLSCoyKg@mail.gmail.com>
Geert Uytterhoeven <geert@linux-m68k•org> writes:
> On Mon, Jul 20, 2020 at 11:03 PM Segher Boessenkool
> <segher@kernel•crashing.org> wrote:
>> On Sat, Jul 18, 2020 at 09:50:50AM +0200, Geert Uytterhoeven wrote:
>> > On Wed, Jun 24, 2020 at 6:02 AM Nathan Chancellor
>> > <natechancellor@gmail•com> wrote:
>> > > /* If we have an image attached to us, it overrides anything
>> > > * supplied by the loader. */
>> > > - if (_initrd_end > _initrd_start) {
>> > > + if (&_initrd_end > &_initrd_start) {
>> >
>> > Are you sure that fix is correct?
>> >
>> > extern char _initrd_start[];
>> > extern char _initrd_end[];
>> > extern char _esm_blob_start[];
>> > extern char _esm_blob_end[];
>> >
>> > Of course the result of their comparison is a constant, as the addresses
>> > are constant. If clangs warns about it, perhaps that warning should be moved
>> > to W=1?
>> >
>> > But adding "&" is not correct, according to C.
>>
>> Why not?
>>
>> 6.5.3.2/3
>> The unary & operator yields the address of its operand. [...]
>> Otherwise, the result is a pointer to the object or function designated
>> by its operand.
>>
>> This is the same as using the name of an array without anything else,
>> yes. It is a bit clearer if it would not be declared as array, perhaps,
>> but it is correct just fine like this.
>
> Thanks, I stand corrected.
>
> Regardless, the comparison is still a comparison between two constant
> addresses, so my fear is that the compiler will start generating
> warnings for that in the near or distant future, making this change
> futile.
They're not constant at compile time though. So I don't think the
compiler could (sensibly) warn about that? (surely!)
cheers
next prev parent reply other threads:[~2020-08-03 11:11 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-24 3:59 [PATCH] powerpc/boot: Use address-of operator on section symbols Nathan Chancellor
2020-06-25 1:18 ` Geoff Levand
2020-06-25 2:22 ` Nathan Chancellor
2020-06-25 16:32 ` Nick Desaulniers
2020-07-18 9:13 ` Arnd Bergmann
2020-07-16 12:56 ` Michael Ellerman
2020-07-18 7:50 ` Geert Uytterhoeven
2020-07-18 15:31 ` Nathan Chancellor
2020-07-20 21:02 ` Segher Boessenkool
2020-08-03 10:06 ` Geert Uytterhoeven
2020-08-03 11:09 ` Michael Ellerman [this message]
2020-08-03 11:32 ` Geert Uytterhoeven
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