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Re: -fpatchable-function-entry: leverage multi-byte NOP on x86

From: Alexander Monakov <amonakov at ispras dot ru>
To: Martin Liška <mliska at suse dot cz>
Cc: Fangrui Song <i at maskray dot me>, gcc at gcc dot gnu dot org, Jan Hubicka <hubicka at ucw dot cz>
Date: Mon, 6 Jan 2020 12:40:04 +0300 (MSK)
Subject: Re: -fpatchable-function-entry: leverage multi-byte NOP on x86
References: <20200104204843.lwyoq3lhvgmi6f5h@gmail.com> <7884fb3e-f26a-46b9-321a-0a78d8c01df5@suse.cz>

On Mon, 6 Jan 2020, Martin Liška wrote:

> You are right, we do not leverage multi-byte NOPs. Note that the support
> depends
> on a CPU model (-march) and the similar code is quite complex in binutils:
> https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=gas/config/tc-i386.c;h=d0b8f2624a1885d83d2595474bfd78ae844f48f2;hb=HEAD#l1441
> 
> I'm not sure how worthy would it be to implement that?

Huh? Surely the right move would be to ask Binutils to expose that via
a new pseudo-op, like .balign but requesting a specific space rather
than aligning up to a boundary.

Alexander

References:
- -fpatchable-function-entry: leverage multi-byte NOP on x86
  - From: Fangrui Song
- Re: -fpatchable-function-entry: leverage multi-byte NOP on x86
  - From: Martin Liška

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