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, 289 insertions, 0 deletions

diff --git a/tools/perf/arch/common.c b/tools/perf/arch/common.c
new file mode 100644
index 000000000..5ad50e331
--- /dev/null
+++ b/tools/perf/arch/common.c
@@ -0,0 +1,289 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "common.h"
+
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <linux/zalloc.h>
+#include <unistd.h>
+
+#include <dwarf-regs.h>
+
+#include "../util/debug.h"
+#include "../util/env.h"
+
+static const char *const arc_triplets[] = {
+	"arc-linux-",
+	"arc-snps-linux-uclibc-",
+	"arc-snps-linux-gnu-",
+	NULL
+};
+
+static const char *const arm_triplets[] = {
+	"arm-eabi-",
+	"arm-linux-androideabi-",
+	"arm-unknown-linux-",
+	"arm-unknown-linux-gnu-",
+	"arm-unknown-linux-gnueabi-",
+	"arm-linux-gnu-",
+	"arm-linux-gnueabihf-",
+	"arm-none-eabi-",
+	NULL
+};
+
+static const char *const arm64_triplets[] = {
+	"aarch64-linux-android-",
+	"aarch64-linux-gnu-",
+	NULL
+};
+
+static const char *const powerpc_triplets[] = {
+	"powerpc-unknown-linux-gnu-",
+	"powerpc-linux-gnu-",
+	"powerpc64-unknown-linux-gnu-",
+	"powerpc64-linux-gnu-",
+	"powerpc64le-linux-gnu-",
+	NULL
+};
+
+static const char *const riscv32_triplets[] = {
+	"riscv32-unknown-linux-gnu-",
+	"riscv32-linux-android-",
+	"riscv32-linux-gnu-",
+	NULL
+};
+
+static const char *const riscv64_triplets[] = {
+	"riscv64-unknown-linux-gnu-",
+	"riscv64-linux-android-",
+	"riscv64-linux-gnu-",
+	NULL
+};
+
+static const char *const s390_triplets[] = {
+	"s390-ibm-linux-",
+	"s390x-linux-gnu-",
+	NULL
+};
+
+static const char *const sh_triplets[] = {
+	"sh-unknown-linux-gnu-",
+	"sh-linux-gnu-",
+	NULL
+};
+
+static const char *const sparc_triplets[] = {
+	"sparc-unknown-linux-gnu-",
+	"sparc64-unknown-linux-gnu-",
+	"sparc64-linux-gnu-",
+	NULL
+};
+
+static const char *const x86_triplets[] = {
+	"x86_64-pc-linux-gnu-",
+	"x86_64-unknown-linux-gnu-",
+	"i686-pc-linux-gnu-",
+	"i586-pc-linux-gnu-",
+	"i486-pc-linux-gnu-",
+	"i386-pc-linux-gnu-",
+	"i686-linux-android-",
+	"i686-android-linux-",
+	"x86_64-linux-gnu-",
+	"i586-linux-gnu-",
+	NULL
+};
+
+static const char *const mips_triplets[] = {
+	"mips-unknown-linux-gnu-",
+	"mipsel-linux-android-",
+	"mips-linux-gnu-",
+	"mips64-linux-gnu-",
+	"mips64el-linux-gnuabi64-",
+	"mips64-linux-gnuabi64-",
+	"mipsel-linux-gnu-",
+	NULL
+};
+
+static bool lookup_path(char *name)
+{
+	bool found = false;
+	char *path, *tmp = NULL;
+	char buf[PATH_MAX];
+	char *env = getenv("PATH");
+
+	if (!env)
+		return false;
+
+	env = strdup(env);
+	if (!env)
+		return false;
+
+	path = strtok_r(env, ":", &tmp);
+	while (path) {
+		scnprintf(buf, sizeof(buf), "%s/%s", path, name);
+		if (access(buf, F_OK) == 0) {
+			found = true;
+			break;
+		}
+		path = strtok_r(NULL, ":", &tmp);
+	}
+	free(env);
+	return found;
+}
+
+static int lookup_triplets(const char *const *triplets, const char *name)
+{
+	int i;
+	char buf[PATH_MAX];
+
+	for (i = 0; triplets[i] != NULL; i++) {
+		scnprintf(buf, sizeof(buf), "%s%s", triplets[i], name);
+		if (lookup_path(buf))
+			return i;
+	}
+	return -1;
+}
+
+static bool is_native_compatible(struct perf_env *env, uint16_t target, uint16_t host)
+{
+	if (target != host) {
+		/* A 64-bit host can natively disassemble its 32-bit compat architecture */
+		if (host == EM_X86_64 && target == EM_386)
+			return true;
+		if (host == EM_AARCH64 && target == EM_ARM)
+			return true;
+		if (host == EM_PPC64 && target == EM_PPC)
+			return true;
+		if (host == EM_SPARCV9 && target == EM_SPARC)
+			return true;
+		return false;
+	}
+
+	/* target == host case */
+	if (target == EM_RISCV) {
+		bool target_is_64 = perf_env__kernel_is_64_bit(env);
+		bool host_is_64 = (sizeof(void *) == 8);
+
+		/* 32-bit host cannot natively disassemble 64-bit target */
+		if (!host_is_64 && target_is_64)
+			return false;
+	}
+
+	return true;
+}
+
+static int perf_env__lookup_binutils_path(struct perf_env *env,
+					  const char *name, char **path)
+{
+	int idx;
+	uint16_t e_machine = perf_env__e_machine(env, /*e_flags=*/NULL);
+	const char *cross_env;
+	const char *const *path_list;
+	char *buf = NULL;
+
+	/*
+	 * We don't need to try to find objdump path for native system.
+	 * Just use default binutils path (e.g.: "objdump").
+	 */
+	if (is_native_compatible(env, e_machine, EM_HOST))
+		goto out;
+
+	cross_env = getenv("CROSS_COMPILE");
+	if (cross_env) {
+		if (asprintf(&buf, "%s%s", cross_env, name) < 0)
+			goto out_error;
+		if (buf[0] == '/') {
+			if (access(buf, F_OK) == 0)
+				goto out;
+			goto out_error;
+		}
+		if (lookup_path(buf))
+			goto out;
+		zfree(&buf);
+	}
+
+	switch (e_machine) {
+	case EM_ARC:
+		path_list = arc_triplets;
+		break;
+	case EM_ARM:
+		path_list = arm_triplets;
+		break;
+	case EM_AARCH64:
+		path_list = arm64_triplets;
+		break;
+	case EM_PPC:
+	case EM_PPC64:
+		path_list = powerpc_triplets;
+		break;
+	case EM_RISCV:
+		path_list = perf_env__kernel_is_64_bit(env) ? riscv64_triplets : riscv32_triplets;
+		break;
+	case EM_SH:
+		path_list = sh_triplets;
+		break;
+	case EM_S390:
+		path_list = s390_triplets;
+		break;
+	case EM_SPARC:
+	case EM_SPARCV9:
+		path_list = sparc_triplets;
+		break;
+	case EM_X86_64:
+	case EM_386:
+		path_list = x86_triplets;
+		break;
+	case EM_MIPS:
+		path_list = mips_triplets;
+		break;
+	default:
+		ui__error("binutils for %s not supported.\n", perf_env__arch(env));
+		goto out_error;
+	}
+
+	idx = lookup_triplets(path_list, name);
+	if (idx < 0) {
+		ui__error("Please install %s for %s.\n"
+			  "You can add it to PATH, set CROSS_COMPILE or "
+			  "override the default using --%s.\n",
+			  name, perf_env__arch(env), name);
+		goto out_error;
+	}
+
+	if (asprintf(&buf, "%s%s", path_list[idx], name) < 0)
+		goto out_error;
+
+out:
+	*path = buf;
+	return 0;
+out_error:
+	free(buf);
+	*path = NULL;
+	return -1;
+}
+
+int perf_env__lookup_objdump(struct perf_env *env, char **path)
+{
+	/*
+	 * For live mode, env->arch will be NULL and we can use
+	 * the native objdump tool.
+	 */
+	if (env->arch == NULL)
+		return 0;
+
+	return perf_env__lookup_binutils_path(env, "objdump", path);
+}
+
+/*
+ * Some architectures have a single address space for kernel and user addresses,
+ * which makes it possible to determine if an address is in kernel space or user
+ * space.
+ */
+bool perf_env__single_address_space(struct perf_env *env)
+{
+	uint16_t e_machine = perf_env__e_machine(env, /*e_flags=*/NULL);
+
+	return e_machine != EM_SPARC && e_machine != EM_SPARCV9 && e_machine != EM_S390;
+}