linux-kernel - Re: [PATCH] x86, retpolines: entirely disable switch jump tables when retpolines are enabled

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Date:   Mon, 25 Mar 2019 14:28:51 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Daniel Borkmann <daniel@...earbox.net>, tglx@...utronix.de
Cc:     linux-kernel@...r.kernel.org, mliska@...e.cz,
        "H . J . Lu" <hjl.tools@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Björn Töpel <bjorn.topel@...el.com>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Alexei Starovoitov <ast@...nel.org>,
        "David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH] x86, retpolines: entirely disable switch jump tables
 when retpolines are enabled

On Mon, 2019-03-25 at 14:56 +0100, Daniel Borkmann wrote:
> More than 20 switch cases are not expected to be fast-path critical, but
> it would still be good to align with gcc behavior for versions < 8.4.0 in
> order to have consistency across supported gcc versions. vmlinux size is
> slightly growing by 0.27% for older gcc. This flag is only set to work
> around affected gcc, no change for clang.

I note your final sentence doesn't actually say that clang doesn't have
this problem, and doesn't *need* this (or an equivalent) change.

It should say that (if it's true). And if it isn't true, then other
remedial action would be in order.


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