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From: "hjl.tools at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/104816] -fcf-protection=branch should generate endbr
 instead of notrack jumps
Date: Fri, 11 Mar 2022 20:43:26 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104816

H.J. Lu <hjl.tools at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |WAITING

--- Comment #8 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Joao Moreira from comment #0)
> When -fcf-protection=3Dbranch is used, the compiler will generate jump ta=
bles
> where the indirect jump is prefixed with the NOTRACK prefix, so it can ju=
mp
> to non-ENDBR targets. Yet, for NOTRACK prefixes to work, the NOTRACK
> specific enable bit must be set, what renders the binary broken on any
> environment where this is not the case. In fact, having NOTRACK disabled =
was
> a design choice for the Linux kernel CET support
> [https://lkml.org/lkml/2022/3/7/1068].
>=20
> With the above, the compiler should generate jump tables with ENDBRs, for
> proper correctness. And, if security regarding the additional ENDBRs is a
> concern, the code can be explicitly compiled with -fno-jump-tables.

There is an undocumented option: -mcet-switch.  It does exactly what you
are looking for.  Currently it is off by default.  We can document it
and turn it on by default.=