Richard Earnshaw <Richard.Earnshaw@foss.arm.com> writes:

[...]

> +@item
> +-mbranch-protection=@var{none}|@var{standard}|@var{pac-ret}[+@var{leaf}][+@var{bti}]|@var{bti}[+@var{pac-ret}[+@var{leaf}]]
> +@opindex mbranch-protection
> +Enable branch protection features (armv8.1-m.main only).
> +@samp{none} generate code without branch protection or return address
> +signing.
> +@samp{standard[+@var{leaf}]} generate code with all branch protection
> +features enabled at their standard level.
> +@samp{pac-ret[+@var{leaf}]} generate code with return address signing
> +set to its standard level, which is to sign all functions that save
> +the return address to memory.
> +@samp{leaf} When return address signing is enabled, also sign leaf
> +functions even if they do not write the return address to memory.
> ++@samp{bti} Add landing-pad instructions at the permitted targets of
> +indirect branch instructions.
> +
> +If the @samp{+pacbti} architecture extension is not enabled, then all
> +branch protection and return address signing operations are
> +constrained to use only the instructions defined in the
> +architectural-NOP space. The generated code will remain
> +backwards-compatible with earlier versions of the architecture, but
> +the additional security can be enabled at run time on processors that
> +support the @samp{PACBTI} extension.
> +
> +Branch target enforcement using BTI can only be enabled at runtime if
> +all code in the application has been compiled with at least
> +@samp{-mbranch-protection=bti}.
> +
> +The default is to generate code without branch protection or return
> +address signing.
>
> This needs to make it clear that -mbranch-protection != none is only
> supported on armv8-m.main or later.
>
> R.

Hi Richard,

thanks for reviewing, please find attached the respinned patch.

Ok for trunk (when the rest of the series will be approved)?

Best Regards

  Andrea

gcc/ChangeLog:

	* config/arm/arm.c (arm_configure_build_target): Parse and validate
	-mbranch-protection option and initialize appropriate data structures.
	* config/arm/arm.opt (-mbranch-protection): New option.
	* doc/invoke.texi (Arm Options): Document it.

Co-Authored-By: Tejas Belagod  <tbelagod@arm.com>
Co-Authored-By: Richard Earnshaw <Richard.Earnshaw@arm.com>