linux-kernel - Re: [GIT PULL] hash addresses printed with %p

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Date:   Mon, 4 Dec 2017 10:03:19 +0000
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Dave Young <dyoung@...hat.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Tobin C. Harding" <me@...in.cc>,
        LKML <linux-kernel@...r.kernel.org>,
        "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>
Subject: Re: [GIT PULL] hash addresses printed with %p

On 4 December 2017 at 09:59, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
> On Mon, Dec 04, 2017 at 09:48:37AM +0000, Ard Biesheuvel wrote:
>> On 4 December 2017 at 09:34, Greg Kroah-Hartman
>> <gregkh@...uxfoundation.org> wrote:
>> > On Mon, Dec 04, 2017 at 05:29:28PM +0800, Dave Young wrote:
>> >> On 12/04/17 at 08:36am, Greg Kroah-Hartman wrote:
>> >> > On Mon, Dec 04, 2017 at 10:02:16AM +0800, Dave Young wrote:
>> >> > > +#define __ATTR_IRUSR(_name) {                                            \
>> >> > > + .attr   = { .name = __stringify(_name), .mode = S_IRUSR },      \
>> >> > > + .show   = _name##_show,                                         \
>> >> > > +}
>> >> >
>> >> > Ick, no, as others, including Linus, have said, using IRUSER is a pain
>> >> > in the ass to try to look up and remember what it is...
>> >> >
>> >> > Just use __ATTR() please, it should be fine for what you need to do,
>> >> > which is special-case a sysfs attribute.
>> >>
>> >> Hmm, I was hesitating to do that because it needs either long code
>> >> (over 80 chars) or some driver internal macros.
>> >>
>> >> There is already same issue in dmi-sysfs.c, it uses an internal macro
>> >> DMI_SYSFS_ATTR for 0400 attr.  I did not search all the kernel code,
>> >> there might be more for such special cases. Maybe we can add some
>> >> comment in sysfs.h to mention this is for some special case?
>> >>
>> >> I can do something similar as dmi sysfs code though.
>> >
>> > Hm, let me look at this this afternoon when I get through some stable
>> > patches, it shouldn't be that complex to need a whole new macro...
>> >
>>
>> But wasn't that the whole point? That there is a macro that does what
>> you don't want (__ATTR_RO) and none that does what you do want?
>
> my point is that __ATTR() should work for you as-is...

Well, not entirely.

Not sure if the runtime-map code is doing anything wrong here, but it defines

struct map_attribute {
    struct attribute attr;
    ssize_t (*show)(struct efi_runtime_map_entry *entry, char *buf);
};

and uses __ATTR_RO() to emit initializers for it. __ATTR() initializes
the .store member as well, which does not exists, and so it cannot be
used directly.

So we should either add a .store member that is always NULL, or we
should add our own

#define __ATTR_0400(_name) { \
.attr = { .name = __stringify(_name), .mode = 0400 }, \
.show = _name##_show, \
}

that does not set .store at all.

-- 
Ard.