linux-kernel - [PATCH] x86/Kconfig: rust: Patchable function Rust compat

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Date:   Mon, 11 Dec 2023 15:07:49 +0000
From:   Matthew Maurer <mmaurer@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>
Cc:     Matthew Maurer <mmaurer@...gle.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        "Björn Roy Baron" <bjorn3_gh@...tonmail.com>,
        Benno Lossin <benno.lossin@...ton.me>,
        Andreas Hindborg <a.hindborg@...sung.com>,
        Alice Ryhl <aliceryhl@...gle.com>,
        linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org
Subject: [PATCH] x86/Kconfig: rust: Patchable function Rust compat

Rust doesn't yet support patchable entry, but likely will soon. Disable
function padding when Rust is used but doesn't support it, and propagate
the flag when it does.

Signed-off-by: Matthew Maurer <mmaurer@...gle.com>
---
 arch/x86/Kconfig  | 6 +++++-
 arch/x86/Makefile | 2 ++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 18b9fb7df95b..e9f1814217b5 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2452,6 +2452,10 @@ config CC_HAS_RETURN_THUNK
 config CC_HAS_ENTRY_PADDING
 	def_bool $(cc-option,-fpatchable-function-entry=16,16)
 
+config RUSTC_HAS_ENTRY_PADDING
+	depends RUST
+	def_bool $(rs-option,-Zpatchable-function-entry=16,16)
+
 config FUNCTION_PADDING_CFI
 	int
 	default 59 if FUNCTION_ALIGNMENT_64B
@@ -2469,7 +2473,7 @@ config FUNCTION_PADDING_BYTES
 
 config CALL_PADDING
 	def_bool n
-	depends on CC_HAS_ENTRY_PADDING && OBJTOOL
+	depends on CC_HAS_ENTRY_PADDING && (!RUST || RUST_HAS_ENTRY_PADDING) && OBJTOOL
 	select FUNCTION_ALIGNMENT_16B
 
 config FINEIBT
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 1a068de12a56..0228af62742e 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -211,7 +211,9 @@ endif
 
 ifdef CONFIG_CALL_PADDING
 PADDING_CFLAGS := -fpatchable-function-entry=$(CONFIG_FUNCTION_PADDING_BYTES),$(CONFIG_FUNCTION_PADDING_BYTES)
+PADDING_RUSTFLAGS := -Zpatchable-function-entry=$(CONFIG_FUNCTION_PADDING_BYTES),$(CONFIG_FUNCTION_PADDING_BYTES)
 KBUILD_CFLAGS += $(PADDING_CFLAGS)
+KBUILD_RUSTFLAGS += $(PADDING_RUSTFLAGS)
 export PADDING_CFLAGS
 endif
 
-- 
2.43.0.472.g3155946c3a-goog