Re: [PATCH] x86: rust: Disable entry padding with Rust

[Dave Hansen]

On 12/15/23 11:39, Matthew Maurer wrote:
> +config HAVE_ENTRY_PADDING
> +	def_bool CC_HAS_ENTRY_PADDING && !RUST

My only worry with this is that we need HAVE_ENTRY_PADDING for:

> config HAVE_CALL_THUNKS
>         def_bool y
>         depends on CC_HAS_ENTRY_PADDING && RETHUNK && OBJTOOL
..
> config CALL_DEPTH_TRACKING
>         bool "Mitigate RSB underflow with call depth tracking"
>         depends on CPU_SUP_INTEL && HAVE_CALL_THUNKS

so if they turn on RUST, they'll end up turning off CALL_DEPTH_TRACKING.
 I'm wondering if it might be better to do this instead (temporarily of
course):

config RUST
        bool "Rust support"
        depends on HAVE_RUST
        depends on RUST_IS_AVAILABLE
        depends on !MODVERSIONS
        depends on !GCC_PLUGINS
        depends on !RANDSTRUCT
        depends on !DEBUG_INFO_BTF || PAHOLE_HAS_LANG_EXCLUDE
+	depends on !CALL_THUNKS

That way, someone who is using CALL_DEPTH_TRACKING doesn't accidentally
lose it by turning on RUST.  To turn on RUST, they'd first need to go
turn off the things that are selecting CALL_THUNKS.