Re: [PATCH] Properly compute offsets of note descriptor and next note [BZ #22370]

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Sat, Nov 25, 2017 at 8:39 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Fri, Nov 24, 2017 at 6:45 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> On Mon, Nov 20, 2017 at 5:04 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>> On Thu, Nov 16, 2017 at 5:24 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>>> On Wed, Nov 15, 2017 at 3:03 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>>>> On Sun, Nov 12, 2017 at 8:03 AM, Andreas Schwab <schwab@linux-m68k.org> wrote:
>>>>>> On Nov 12 2017, "H.J. Lu" <hjl.tools@gmail.com> wrote:
>>>>>>
>>>>>>> Data after Elf64_Nhdr is the "name" field which is a 4-byte string, "GNU".
>>>>>>> There is no misalignment.
>>>>>>
>>>>>> That's not what your patch does.  You are aligning both the name length
>>>>>> and the data length to a 8 byte boundary, making the note size
>>>>>> unaligned.
>>>>>>
>>>>>
>>>>> You are right.  Both glibc and binutils get this wrong.  I opened a
>>>>> binutils bug:
>>>>>
>>>>> https://sourceware.org/bugzilla/show_bug.cgi?id=22444
>>>>>
>>>>> I will fix it first and take care of glibc next.
>>>>>
>>>>
>>>> Here is the glibc path.
>>>>
>>>> Any comments?
>>>>
>>>
>>> Any comments or objections?
>>>
>>
>> I updated Linux Extensions to gABI to clarify alignments of NOTE section
>> and segments:
>>
>> https://sourceware.org/ml/gnu-gabi/2017-q4/msg00003.html
>>
>> I will check it in next week.
>>
>
> Here is the updated patch I will check in next week.  It added:
>
> +     /* NB: Some PT_NOTE segment may have alignment value of 0
> +        or 1.  gABI specifies that PT_NOTE segments should be
> +        aligned to 4 bytes in 32-bit objects and to 8 bytes in
> +        64-bit objects.  As a Linux extension, we also support
> +        4 byte alignment in 64-bit objects.  If p_align is less
> +        than 4, we treate alignment as 4 bytes.   */
> +     ElfW(Addr) align = phdr[i].p_align;
> +     if (align < 4)
> +       align = 4;
>
> to prevent infinite loop with incorrect segment alignment.
>

This is the final patch I am checking in now.  I added:

+     if (align < 4)
+       align = 4;
+     else if (align != 4 && align != 8)
+       continue;

to skip note segments which aren't aligned to 8 bytes and 4 bytes or
less.

-- 
H.J.

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