From: Daniel Micay <danielmicay@gmail.com>
Subject: Re: x86: PIE support and option to extend KASLR randomization
Date: Wed, 16 Aug 2017 12:26:36 -0400
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Cc: Herbert Xu <herbert@gondor.apana.org.au>, "David S . Miller"
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To: Ingo Molnar <mingo@kernel.org>, Thomas Garnier <thgarnie@google.com>
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> How are these assumptions hardcoded by GCC? Most of the instructions
> should be 
> relocatable straight away, as most call/jump/branch instructions are
> RIP-relative.
> 
> I.e. is there no GCC code generation mode where code can be placed
> anywhere in the 
> canonical address space, yet call and jump distance is within 31 bits
> so that the 
> generated code is fast?

That's what PIE is meant to do. However, not disabling support for lazy
linking (-fno-plt) / symbol interposition (-Bsymbolic) is going to cause
it to add needless overhead.

arm64 is using -pie -shared -Bsymbolic in arch/arm64/Makefile for their
CONFIG_RELOCATABLE option. See 08cc55b2afd97a654f71b3bebf8bb0ec89fdc498.