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, 79 insertions, 0 deletions

diff --git a/include/soc/qcom/tcs.h b/include/soc/qcom/tcs.h
new file mode 100644
index 000000000..cff67ce25
--- /dev/null
+++ b/include/soc/qcom/tcs.h
@@ -0,0 +1,79 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2016-2019, The Linux Foundation. All rights reserved.
+ */
+
+#ifndef __SOC_QCOM_TCS_H__
+#define __SOC_QCOM_TCS_H__
+
+#include <linux/bitfield.h>
+#include <linux/bits.h>
+
+#define MAX_RPMH_PAYLOAD	16
+
+/**
+ * rpmh_state: state for the request
+ *
+ * RPMH_SLEEP_STATE:       State of the resource when the processor subsystem
+ *                         is powered down. There is no client using the
+ *                         resource actively.
+ * RPMH_WAKE_ONLY_STATE:   Resume resource state to the value previously
+ *                         requested before the processor was powered down.
+ * RPMH_ACTIVE_ONLY_STATE: Active or AMC mode requests. Resource state
+ *                         is aggregated immediately.
+ */
+enum rpmh_state {
+	RPMH_SLEEP_STATE,
+	RPMH_WAKE_ONLY_STATE,
+	RPMH_ACTIVE_ONLY_STATE,
+};
+
+/**
+ * struct tcs_cmd: an individual request to RPMH.
+ *
+ * @addr: the address of the resource slv_id:18:16 | offset:0:15
+ * @data: the resource state request
+ * @wait: ensure that this command is complete before returning.
+ *        Setting "wait" here only makes sense during rpmh_write_batch() for
+ *        active-only transfers, this is because:
+ *        rpmh_write() - Always waits.
+ *                       (DEFINE_RPMH_MSG_ONSTACK will set .wait_for_compl)
+ *        rpmh_write_async() - Never waits.
+ *                       (There's no request completion callback)
+ */
+struct tcs_cmd {
+	u32 addr;
+	u32 data;
+	u32 wait;
+};
+
+/**
+ * struct tcs_request: A set of tcs_cmds sent together in a TCS
+ *
+ * @state:          state for the request.
+ * @wait_for_compl: wait until we get a response from the h/w accelerator
+ *                  (same as setting cmd->wait for all commands in the request)
+ * @num_cmds:       the number of @cmds in this request
+ * @cmds:           an array of tcs_cmds
+ */
+struct tcs_request {
+	enum rpmh_state state;
+	u32 wait_for_compl;
+	u32 num_cmds;
+	struct tcs_cmd *cmds;
+};
+
+#define BCM_TCS_CMD_COMMIT_MASK		BIT(30)
+#define BCM_TCS_CMD_VALID_MASK		BIT(29)
+#define BCM_TCS_CMD_VOTE_MASK		GENMASK(13, 0)
+#define BCM_TCS_CMD_VOTE_Y_MASK		GENMASK(13, 0)
+#define BCM_TCS_CMD_VOTE_X_MASK		GENMASK(27, 14)
+
+/* Construct a Bus Clock Manager (BCM) specific TCS command */
+#define BCM_TCS_CMD(commit, valid, vote_x, vote_y)		\
+	(u32_encode_bits(commit, BCM_TCS_CMD_COMMIT_MASK) |	\
+	u32_encode_bits(valid, BCM_TCS_CMD_VALID_MASK) |	\
+	u32_encode_bits(vote_x, BCM_TCS_CMD_VOTE_X_MASK) |	\
+	u32_encode_bits(vote_y, BCM_TCS_CMD_VOTE_Y_MASK))
+
+#endif /* __SOC_QCOM_TCS_H__ */