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, 177 insertions, 0 deletions

diff --git a/drivers/cpufreq/amd-pstate-trace.h b/drivers/cpufreq/amd-pstate-trace.h
new file mode 100644
index 000000000..91fa073b2
--- /dev/null
+++ b/drivers/cpufreq/amd-pstate-trace.h
@@ -0,0 +1,177 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * amd-pstate-trace.h - AMD Processor P-state Frequency Driver Tracer
+ *
+ * Copyright (C) 2021 Advanced Micro Devices, Inc. All Rights Reserved.
+ *
+ * Author: Huang Rui <ray.huang@amd.com>
+ */
+
+#if !defined(_AMD_PSTATE_TRACE_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _AMD_PSTATE_TRACE_H
+
+#include <linux/cpufreq.h>
+#include <linux/tracepoint.h>
+#include <linux/trace_events.h>
+
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM amd_cpu
+
+#undef TRACE_INCLUDE_FILE
+#define TRACE_INCLUDE_FILE amd-pstate-trace
+
+#define TPS(x)  tracepoint_string(x)
+
+TRACE_EVENT(amd_pstate_perf,
+
+	TP_PROTO(u8 min_perf,
+		 u8 target_perf,
+		 u8 capacity,
+		 u64 freq,
+		 u64 mperf,
+		 u64 aperf,
+		 u64 tsc,
+		 unsigned int cpu_id,
+		 bool fast_switch
+		 ),
+
+	TP_ARGS(min_perf,
+		target_perf,
+		capacity,
+		freq,
+		mperf,
+		aperf,
+		tsc,
+		cpu_id,
+		fast_switch
+		),
+
+	TP_STRUCT__entry(
+		__field(u8, min_perf)
+		__field(u8, target_perf)
+		__field(u8, capacity)
+		__field(unsigned long long, freq)
+		__field(unsigned long long, mperf)
+		__field(unsigned long long, aperf)
+		__field(unsigned long long, tsc)
+		__field(unsigned int, cpu_id)
+		__field(bool, fast_switch)
+		),
+
+	TP_fast_assign(
+		__entry->min_perf = min_perf;
+		__entry->target_perf = target_perf;
+		__entry->capacity = capacity;
+		__entry->freq = freq;
+		__entry->mperf = mperf;
+		__entry->aperf = aperf;
+		__entry->tsc = tsc;
+		__entry->cpu_id = cpu_id;
+		__entry->fast_switch = fast_switch;
+		),
+
+	TP_printk("amd_min_perf=%hhu amd_des_perf=%hhu amd_max_perf=%hhu freq=%llu mperf=%llu aperf=%llu tsc=%llu cpu_id=%u fast_switch=%s",
+		  (u8)__entry->min_perf,
+		  (u8)__entry->target_perf,
+		  (u8)__entry->capacity,
+		  (unsigned long long)__entry->freq,
+		  (unsigned long long)__entry->mperf,
+		  (unsigned long long)__entry->aperf,
+		  (unsigned long long)__entry->tsc,
+		  (unsigned int)__entry->cpu_id,
+		  (__entry->fast_switch) ? "true" : "false"
+		 )
+);
+
+TRACE_EVENT(amd_pstate_epp_perf,
+
+	TP_PROTO(unsigned int cpu_id,
+		 u8 highest_perf,
+		 u8 epp,
+		 u8 min_perf,
+		 u8 max_perf,
+		 bool boost,
+		 bool changed
+		 ),
+
+	TP_ARGS(cpu_id,
+		highest_perf,
+		epp,
+		min_perf,
+		max_perf,
+		boost,
+		changed),
+
+	TP_STRUCT__entry(
+		__field(unsigned int, cpu_id)
+		__field(u8, highest_perf)
+		__field(u8, epp)
+		__field(u8, min_perf)
+		__field(u8, max_perf)
+		__field(bool, boost)
+		__field(bool, changed)
+		),
+
+	TP_fast_assign(
+		__entry->cpu_id = cpu_id;
+		__entry->highest_perf = highest_perf;
+		__entry->epp = epp;
+		__entry->min_perf = min_perf;
+		__entry->max_perf = max_perf;
+		__entry->boost = boost;
+		__entry->changed = changed;
+		),
+
+	TP_printk("cpu%u: [%hhu<->%hhu]/%hhu, epp=%hhu, boost=%u, changed=%u",
+		  (unsigned int)__entry->cpu_id,
+		  (u8)__entry->min_perf,
+		  (u8)__entry->max_perf,
+		  (u8)__entry->highest_perf,
+		  (u8)__entry->epp,
+		  (bool)__entry->boost,
+		  (bool)__entry->changed
+		 )
+);
+
+TRACE_EVENT(amd_pstate_cppc_req2,
+
+	TP_PROTO(unsigned int cpu_id,
+		 u8 floor_perf,
+		 bool changed,
+		 int err_code
+		 ),
+
+	TP_ARGS(cpu_id,
+		floor_perf,
+		changed,
+		err_code),
+
+	TP_STRUCT__entry(
+		__field(unsigned int, cpu_id)
+		__field(u8, floor_perf)
+		__field(bool, changed)
+		__field(int, err_code)
+		),
+
+	TP_fast_assign(
+		__entry->cpu_id = cpu_id;
+		__entry->floor_perf = floor_perf;
+		__entry->changed = changed;
+		__entry->err_code = err_code;
+		),
+
+	TP_printk("cpu%u: floor_perf=%u, changed=%u (error = %d)",
+		  __entry->cpu_id,
+		  __entry->floor_perf,
+		  __entry->changed,
+		  __entry->err_code
+		 )
+);
+
+#endif /* _AMD_PSTATE_TRACE_H */
+
+/* This part must be outside protection */
+#undef TRACE_INCLUDE_PATH
+#define TRACE_INCLUDE_PATH .
+
+#include <trace/define_trace.h>