[PATCH 0/6] ld: Add "-z textonly" option to ELF linker

[H.J. Lu]

On Tue, Nov 14, 2017 at 6:41 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Tue, Nov 14, 2017 at 5:58 AM, Michael Matz <matz@suse.de> wrote:
>> Hi,
>>
>> On Tue, 14 Nov 2017, H.J. Lu wrote:
>>
>>> > This is the result of the above problem, but it's not necessary.  Like in
>>> > a traditional two-LOAD-segment file, which also isn't larger than 2MB,
>>> > just because the page size is 2MB.  It achieves this by mapping the same
>>> > file bytes multiple times, and you could do the same.  E.g. for the file
>>> > above the better layout would be:
>>> >
>>> >   LOAD           0x000000 0x00000000 0x00000000 0x00200 0x00200 R   0x200000
>>> >   LOAD           0x000fd0 0x00200fd0 0x00200fd0 0x0002b 0x0002b R E 0x200000
>>> >   LOAD           0x001000 0x00201000 0x00201000 0x00058 0x00058 R   0x200000
>>> >   LOAD           0x001060 0x00401060 0x00401060 0x000a0 0x000a0 RW  0x200000
>>> >
>>> > But even then something is wrong: The RE and the second R page are both
>>> > mapped onto 0x0020xxxx, i.e. the same 2MB page, so can't have different
>>> > protections.  (You'd need 4k pages again, which defeats the whole purpose
>>> > of having 2MB pages in the file to start with).
>>>
>>> You have found out yourself that it is impossible.
>>
>> Well, as is the above makes not much sense.  It wants to stay at 2MB
>> alignment but can't actually make use of it due to having protection
>> changes within one 2MB page (from RE to R).  Hmm, which means the very
>> introduction of GNU_RELRO already broke the whole 2MB pages optimization
>> :-/ You're just increasing this detrimental effect to now also cause
>> uselessly huge files.
>
> GNU_RELRO is intended for common page size, which is 4K on x86-64.  If
> the page size is 2MB at run-time, GNU_RELRO isn't applied.
>
>> Probably 4k pages should be default with "-z textonly"  Hmpf :(
>
> We can discuss this after "-z textonly" is checked in.
>

Given what happened, I'd like to check this patch set into binutils 2.30.

-- 
H.J.