Re: [PATCH] x86: Generate PLT relocations for -z now

[Szabolcs Nagy <szabolcs.nagy@arm.com>]

On 09/05/17 15:24, Carlos O'Donell wrote:
> On 05/08/2017 04:21 PM, H.J. Lu wrote:
>>
>> This patch partially reverses:
>>
>> commit 25070364b0ce33eed46aa5d78ebebbec6accec7e
>> Author: H.J. Lu <hjl.tools@gmail.com>
>> Date:   Sat May 16 07:00:21 2015 -0700
>>
>>     Don't generate PLT relocations for now binding
>>
>> to support LD_AUDIT and LD_PROFILE with -z now.  If there is an existing
>> GOT relocation, it is still used to avoid PLT relocation against the same
>> function symbol.
>>
>> Any comments?
> I'm testing this on x86_64 locally to make sure it meets the needs of the
> Fedora and Red Hat users that are actively making use of LD_AUDIT.
> 
> Thanks for looking into this and supporting developer tooling that works
> in binutils 2.25, but broke in 2.26 and onwards.
> 

i don't think plt should be considered to be part of the dso abi,
so removing plt relocs should be safe (making a GOT-indirect call
is a valid optimization, since plt is only there for lazy binding
which is an optimization too, gcc can change plt relocs to noplt
ones without -fno-plt so relying on it was never safe).

Alexander Monakov pointed out to me that ld audit could be fixed
in principle to work with GOT-indirect calls e.g. by generating
its entry point trampolines on the fly.