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Re: PT_NOTE alignment, NT_GNU_PROPERTY_TYPE_0, glibc and gold

On 08/16/2018 09:16 PM, Mark Wielaard wrote:
On Thu, Aug 16, 2018 at 04:21:05PM +0200, Florian Weimer wrote:
On 08/16/2018 03:39 PM, H.J. Lu wrote:
glibc only discards 4-byte aligned NT_GNU_PROPERTY_TYPE_0 note
since NT_GNU_PROPERTY_TYPE_0 note follows gABI.  If gold
generates 4 byte alignment, it is a gold bug.

I filed:

I don't think this is a bug in gold, but one in ld:

In the GNU abi all ELF Notes are arrays of 32bit words
(and so 4-byte aligned). This is the same for most other
ELF systems. Making the ELF Notes fields 64bit words (and
so 8-byte aligned) in ELFCLASS64 would indeed be what gabi
literally says, but not what GNU systems, and others, follow.

The binaries are already out there and will be around for a while, even if we reduce the alignment now. So generic ELF parsers need to cope with these binaries anyway.

Having a mix of 4-byte words and 8-byte words ELF Notes
in the same ELF file seems unnecessarily confusing and
introduces extra segments and sections.

There are no 8-byte word ELF notes on GNU systems, that's an HP-UX feature. The new 8-byte-aligned notes still have a four-byte header.

But like you, I don't yet see the value of the 8-byte alignment. We could decide that the current gold behavior is valid, fix glibc, and move on.


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