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, 175 insertions, 0 deletions

diff --git a/lib/dhry_2.c b/lib/dhry_2.c
new file mode 100644
index 000000000..c19e661f3
--- /dev/null
+++ b/lib/dhry_2.c
@@ -0,0 +1,175 @@
+// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+/*
+ ****************************************************************************
+ *
+ *                   "DHRYSTONE" Benchmark Program
+ *                   -----------------------------
+ *
+ *  Version:    C, Version 2.1
+ *
+ *  File:       dhry_2.c (part 3 of 3)
+ *
+ *  Date:       May 25, 1988
+ *
+ *  Author:     Reinhold P. Weicker
+ *
+ ****************************************************************************
+ */
+
+#include "dhry.h"
+
+#include <linux/string.h>
+
+
+static Boolean Func_3(Enumeration Enum_Par_Val)
+/***************************/
+/* executed once        */
+/* Enum_Par_Val == Ident_3 */
+{
+	Enumeration Enum_Loc;
+
+	Enum_Loc = Enum_Par_Val;
+	if (Enum_Loc == Ident_3) {
+		/* then, executed */
+		return true;
+	} else {
+		/* not executed */
+		return false;
+	}
+} /* Func_3 */
+
+
+void Proc_6(Enumeration  Enum_Val_Par, Enumeration *Enum_Ref_Par)
+/*********************************/
+/* executed once */
+/* Enum_Val_Par == Ident_3, Enum_Ref_Par becomes Ident_2 */
+{
+	*Enum_Ref_Par = Enum_Val_Par;
+	if (!Func_3(Enum_Val_Par)) {
+		/* then, not executed */
+		*Enum_Ref_Par = Ident_4;
+	}
+	switch (Enum_Val_Par) {
+	case Ident_1:
+		*Enum_Ref_Par = Ident_1;
+		break;
+	case Ident_2:
+		if (Int_Glob > 100) {
+			/* then */
+			*Enum_Ref_Par = Ident_1;
+		} else {
+			*Enum_Ref_Par = Ident_4;
+		}
+		break;
+	case Ident_3: /* executed */
+		*Enum_Ref_Par = Ident_2;
+		break;
+	case Ident_4:
+		break;
+	case Ident_5:
+		*Enum_Ref_Par = Ident_3;
+		break;
+	} /* switch */
+} /* Proc_6 */
+
+
+void Proc_7(One_Fifty Int_1_Par_Val, One_Fifty Int_2_Par_Val, One_Fifty *Int_Par_Ref)
+/**********************************************/
+/* executed three times                                      */
+/* first call:      Int_1_Par_Val == 2, Int_2_Par_Val == 3,  */
+/*                  Int_Par_Ref becomes 7                    */
+/* second call:     Int_1_Par_Val == 10, Int_2_Par_Val == 5, */
+/*                  Int_Par_Ref becomes 17                   */
+/* third call:      Int_1_Par_Val == 6, Int_2_Par_Val == 10, */
+/*                  Int_Par_Ref becomes 18                   */
+{
+	One_Fifty Int_Loc;
+
+	Int_Loc = Int_1_Par_Val + 2;
+	*Int_Par_Ref = Int_2_Par_Val + Int_Loc;
+} /* Proc_7 */
+
+
+void Proc_8(Arr_1_Dim Arr_1_Par_Ref, Arr_2_Dim Arr_2_Par_Ref, int Int_1_Par_Val, int Int_2_Par_Val)
+/*********************************************************************/
+/* executed once      */
+/* Int_Par_Val_1 == 3 */
+/* Int_Par_Val_2 == 7 */
+{
+	One_Fifty Int_Index;
+	One_Fifty Int_Loc;
+
+	Int_Loc = Int_1_Par_Val + 5;
+	Arr_1_Par_Ref[Int_Loc] = Int_2_Par_Val;
+	Arr_1_Par_Ref[Int_Loc+1] = Arr_1_Par_Ref[Int_Loc];
+	Arr_1_Par_Ref[Int_Loc+30] = Int_Loc;
+	for (Int_Index = Int_Loc; Int_Index <= Int_Loc+1; ++Int_Index)
+		Arr_2_Par_Ref[Int_Loc][Int_Index] = Int_Loc;
+	Arr_2_Par_Ref[Int_Loc][Int_Loc-1] += 1;
+	Arr_2_Par_Ref[Int_Loc+20][Int_Loc] = Arr_1_Par_Ref[Int_Loc];
+	Int_Glob = 5;
+} /* Proc_8 */
+
+
+Enumeration Func_1(Capital_Letter Ch_1_Par_Val, Capital_Letter Ch_2_Par_Val)
+/*************************************************/
+/* executed three times                                         */
+/* first call:      Ch_1_Par_Val == 'H', Ch_2_Par_Val == 'R'    */
+/* second call:     Ch_1_Par_Val == 'A', Ch_2_Par_Val == 'C'    */
+/* third call:      Ch_1_Par_Val == 'B', Ch_2_Par_Val == 'C'    */
+{
+	Capital_Letter Ch_1_Loc;
+	Capital_Letter Ch_2_Loc;
+
+	Ch_1_Loc = Ch_1_Par_Val;
+	Ch_2_Loc = Ch_1_Loc;
+	if (Ch_2_Loc != Ch_2_Par_Val) {
+		/* then, executed */
+		return Ident_1;
+	} else {
+		/* not executed */
+		Ch_1_Glob = Ch_1_Loc;
+		return Ident_2;
+	}
+} /* Func_1 */
+
+
+Boolean Func_2(Str_30 Str_1_Par_Ref, Str_30 Str_2_Par_Ref)
+/*************************************************/
+/* executed once */
+/* Str_1_Par_Ref == "DHRYSTONE PROGRAM, 1'ST STRING" */
+/* Str_2_Par_Ref == "DHRYSTONE PROGRAM, 2'ND STRING" */
+{
+	One_Thirty Int_Loc;
+	Capital_Letter Ch_Loc;
+
+	Int_Loc = 2;
+	while (Int_Loc <= 2) {
+		/* loop body executed once */
+		if (Func_1(Str_1_Par_Ref[Int_Loc],
+			   Str_2_Par_Ref[Int_Loc+1]) == Ident_1) {
+			/* then, executed */
+			Ch_Loc = 'A';
+			Int_Loc += 1;
+		}
+	} /* if, while */
+	if (Ch_Loc >= 'W' && Ch_Loc < 'Z') {
+		/* then, not executed */
+		Int_Loc = 7;
+	}
+	if (Ch_Loc == 'R') {
+		/* then, not executed */
+		return true;
+	} else {
+		/* executed */
+		if (strcmp(Str_1_Par_Ref, Str_2_Par_Ref) > 0) {
+			/* then, not executed */
+			Int_Loc += 7;
+			Int_Glob = Int_Loc;
+			return true;
+		} else {
+			/* executed */
+			return false;
+		}
+	} /* if Ch_Loc */
+} /* Func_2 */