kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 34 insertions, 0 deletions

diff --git a/io_uring/tctx.h b/io_uring/tctx.h
new file mode 100644
index 000000000..76ad1ad45
--- /dev/null
+++ b/io_uring/tctx.h
@@ -0,0 +1,34 @@
+// SPDX-License-Identifier: GPL-2.0
+
+struct io_tctx_node {
+	struct list_head	ctx_node;
+	struct task_struct	*task;
+	struct io_ring_ctx	*ctx;
+};
+
+struct io_uring_task *io_uring_alloc_task_context(struct task_struct *task,
+						  struct io_ring_ctx *ctx);
+void io_uring_del_tctx_node(unsigned long index);
+int __io_uring_add_tctx_node(struct io_ring_ctx *ctx);
+int __io_uring_add_tctx_node_from_submit(struct io_ring_ctx *ctx);
+void io_uring_clean_tctx(struct io_uring_task *tctx);
+void io_uring_free_tctx(struct task_struct *tsk);
+
+void io_uring_unreg_ringfd(void);
+int io_ringfd_register(struct io_ring_ctx *ctx, void __user *__arg,
+		       unsigned nr_args);
+int io_ringfd_unregister(struct io_ring_ctx *ctx, void __user *__arg,
+			 unsigned nr_args);
+
+/*
+ * Note that this task has used io_uring. We use it for cancelation purposes.
+ */
+static inline int io_uring_add_tctx_node(struct io_ring_ctx *ctx)
+{
+	struct io_uring_task *tctx = current->io_uring;
+
+	if (likely(tctx && tctx->last == ctx))
+		return 0;
+
+	return __io_uring_add_tctx_node_from_submit(ctx);
+}