tree 863488c9d9c9c21d367ce3cdca6ef074b26341ee
parent 36605ea2f0d0cfd40fbdfa90ab7083c0b4bc4b4b
author Ties Stuij <ties.stuij@arm.com> 1638354139 +0000
committer Copybara-Service <copybara-worker@google.com> 1638355296 -0800

[clang][ARM] PACBTI-M frontend support

Handle branch protection option on the commandline as well as a function
attribute. One patch for both mechanisms, as they use the same underlying
parsing mechanism.

These are recorded in a set of LLVM IR module-level attributes like we do for
AArch64 PAC/BTI (see https://reviews.llvm.org/D85649):

- command-line options are "translated" to module-level LLVM IR
  attributes (metadata).

- functions have PAC/BTI specific attributes iff the
  __attribute__((target("branch-protection=...))) was used in the function
  declaration.

- command-line option -mbranch-protection to armclang targeting Arm,
following this grammar:

branch-protection ::= "-mbranch-protection=" <protection>
protection ::=  "none" | "standard" | "bti" [ "+" <pac-ret-clause> ]
                | <pac-ret-clause> [ "+" "bti"]
pac-ret-clause ::= "pac-ret" [ "+" <pac-ret-option> ]
pac-ret-option ::= "leaf" ["+" "b-key"] | "b-key" ["+" "leaf"]

b-key is simply a placeholder to make it consistent with AArch64's
version. In Arm, however, it triggers a warning informing that b-key is
unsupported and a-key will be selected instead.

- Handle _attribute_((target(("branch-protection=..."))) for AArch32 with the
same grammer as the commandline options.

This patch is part of a series that adds support for the PACBTI-M extension of
the Armv8.1-M architecture, as detailed here:

https://community.arm.com/arm-community-blogs/b/architectures-and-processors-blog/posts/armv8-1-m-pointer-authentication-and-branch-target-identification-extension

The PACBTI-M specification can be found in the Armv8-M Architecture Reference
Manual:

https://developer.arm.com/documentation/ddi0553/latest

The following people contributed to this patch:

- Momchil Velikov
- Victor Campos
- Ties Stuij

Reviewed By: vhscampos

Differential Revision: https://reviews.llvm.org/D112421

GitOrigin-RevId: e3b2f0226bc09f16d5cdba9b94d1db3f15ee7d4a