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Date:   Mon, 11 Dec 2023 15:07:49 +0000
Mime-Version: 1.0
Message-ID: <20231211150753.293883-1-mmaurer@google.com>
Subject: [PATCH] x86/Kconfig: rust: Patchable function Rust compat
From:   Matthew Maurer <mmaurer@google.com>
To:     Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Wedson Almeida Filho <wedsonaf@gmail.com>
Cc:     Matthew Maurer <mmaurer@google.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        "=?UTF-8?q?Bj=C3=B6rn=20Roy=20Baron?=" <bjorn3_gh@protonmail.com>,
        Benno Lossin <benno.lossin@proton.me>,
        Andreas Hindborg <a.hindborg@samsung.com>,
        Alice Ryhl <aliceryhl@google.com>,
        linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

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@google.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