Re: What integer type should ELF note header have?

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

On Fri, Dec 15, 2017 at 7:38 AM, Mark Wielaard <mark@klomp.org> wrote:
> On Thu, 2017-12-14 at 08:39 -0800, H.J. Lu wrote:
>> > > > BTW. What is the reason you need 8 byte aligned notes?
>> > >
>> > > NT_GNU_PROPERTY_TYPE_0 can have 64-bit integer properties
>> > > in 64-bit objects.  They should be aligned to 8 bytes.
>> >
>> > Not necessarily. You can have not naturally aligned data in files.
>> > ELF
>> > files are cross architectures, so you have to account for different
>>
>> 64-bit integers in NT_GNU_PROPERTY_TYPE_0 note are naturally aligned
>> by design so that int64 can be used to access 64-bit integers in
>> NT_GNU_PROPERTY_TYPE_0 note on all architectures.
>>
>> > alignments and endian issues anyway. Is there a specific property
>> > of
>> > these 64-bit integers that require them to be 8 byte aligned in the
>> > note descriptor data?
>>
>> Currently it has GNU_PROPERTY_STACK_SIZE as 64-bit integer
>> in 64-bit objects.  We may add more in the future.
>
> So is it just convenience, so you don't have to write a
> read_8byte_unaligned_value macro to read the data in the note?
>
> I sympathize that reading note data can be a bit of a pain because you
> cannot rely on the data being naturally aligned. But I am unsure that
> is such a big trouble that it needs new alignment/layout rules.
>

One of NT_GNU_PROPERTY_TYPE_0 note consumers is program
loader.  I believe 64-bit integers in NT_GNU_PROPERTY_TYPE_0 note
should be naturally aligned.

H.J.