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, 253 insertions, 0 deletions

diff --git a/drivers/firewire/device-attribute-test.c b/drivers/firewire/device-attribute-test.c
new file mode 100644
index 000000000..97478a96d
--- /dev/null
+++ b/drivers/firewire/device-attribute-test.c
@@ -0,0 +1,253 @@
+// SPDX-License-Identifier: GPL-2.0-only
+//
+// device-attribute-test.c - An application of Kunit to test implementation for device attributes.
+//
+// Copyright (c) 2023 Takashi Sakamoto
+//
+// This file can not be built independently since it is intentionally included in core-device.c.
+
+#include <kunit/test.h>
+
+// Configuration ROM for AV/C Devices 1.0 (Dec. 12, 2000, 1394 Trading Association)
+// Annex C:Configuration ROM example(informative)
+// C.1 Simple AV/C device
+//
+// Copied from the documentation.
+static const u32 simple_avc_config_rom[] = {
+	0x0404eabf,
+	0x31333934,
+	0xe0646102,
+	0xffffffff,
+	0xffffffff,
+	0x00063287, // root directory.
+	0x03ffffff,
+	0x8100000a,
+	0x17ffffff,
+	0x8100000e,
+	0x0c0083c0,
+	0xd1000001,
+	0x0004442d, // unit 0 directory.
+	0x1200a02d,
+	0x13010001,
+	0x17ffffff,
+	0x81000007,
+	0x0005c915, // leaf for textual descriptor.
+	0x00000000,
+	0x00000000,
+	0x56656e64,
+	0x6f72204e,
+	0x616d6500,
+	0x00057f16, // leaf for textual descriptor.
+	0x00000000,
+	0x00000000,
+	0x4d6f6465,
+	0x6c204e61,
+	0x6d650000,
+};
+
+// Ibid.
+// Annex A:Consideration for configuration ROM reader design (informative)
+// A.1 Vendor directory
+//
+// Written by hand.
+static const u32 legacy_avc_config_rom[] = {
+	0x04199fe7,
+	0x31333934,
+	0xe0644000,
+	0x00112233,
+	0x44556677,
+	0x0005dace, // root directory.
+	0x03012345,
+	0x0c0083c0,
+	0x8d000009,
+	0xd1000002,
+	0xc3000004,
+	0x0002e107, // unit 0 directory.
+	0x12abcdef,
+	0x13543210,
+	0x0002cb73, // vendor directory.
+	0x17fedcba,
+	0x81000004,
+	0x00026dc1, // leaf for EUI-64.
+	0x00112233,
+	0x44556677,
+	0x00050e84, // leaf for textual descriptor.
+	0x00000000,
+	0x00000000,
+	0x41424344,
+	0x45464748,
+	0x494a0000,
+};
+
+static void device_attr_simple_avc(struct kunit *test)
+{
+	static const struct fw_device node = {
+		.device = {
+			.type = &fw_device_type,
+		},
+		.config_rom = simple_avc_config_rom,
+		.config_rom_length = sizeof(simple_avc_config_rom),
+	};
+	static const struct fw_unit unit0 = {
+		.device = {
+			.type = &fw_unit_type,
+			.parent = (struct device *)&node.device,
+		},
+		.directory = &simple_avc_config_rom[12],
+	};
+	struct device *node_dev = (struct device *)&node.device;
+	struct device *unit0_dev = (struct device *)&unit0.device;
+	static const int unit0_expected_ids[] = {0x00ffffff, 0x00ffffff, 0x0000a02d, 0x00010001};
+	char *buf = kunit_kzalloc(test, PAGE_SIZE, GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, buf);
+	int ids[4] = {0, 0, 0, 0};
+
+	// Ensure associations for node and unit devices.
+
+	KUNIT_ASSERT_TRUE(test, is_fw_device(node_dev));
+	KUNIT_ASSERT_FALSE(test, is_fw_unit(node_dev));
+	KUNIT_ASSERT_PTR_EQ(test, fw_device(node_dev), &node);
+
+	KUNIT_ASSERT_FALSE(test, is_fw_device(unit0_dev));
+	KUNIT_ASSERT_TRUE(test, is_fw_unit(unit0_dev));
+	KUNIT_ASSERT_PTR_EQ(test, fw_parent_device((&unit0)), &node);
+	KUNIT_ASSERT_PTR_EQ(test, fw_unit(unit0_dev), &unit0);
+
+	// For entries in root directory.
+
+	// Vendor immediate entry is found.
+	KUNIT_EXPECT_GT(test, show_immediate(node_dev, &config_rom_attributes[0].attr, buf), 0);
+	KUNIT_EXPECT_STREQ(test, buf, "0xffffff\n");
+
+	// Model immediate entry is found.
+	KUNIT_EXPECT_GT(test, show_immediate(node_dev, &config_rom_attributes[4].attr, buf), 0);
+	KUNIT_EXPECT_STREQ(test, buf, "0xffffff\n");
+
+	// Descriptor leaf entry for vendor is found.
+	KUNIT_EXPECT_GT(test, show_text_leaf(node_dev, &config_rom_attributes[5].attr, buf), 0);
+	KUNIT_EXPECT_STREQ(test, buf, "Vendor Name\n");
+
+	// Descriptor leaf entry for model is found.
+	KUNIT_EXPECT_GT(test, show_text_leaf(node_dev, &config_rom_attributes[6].attr, buf), 0);
+	KUNIT_EXPECT_STREQ(test, buf, "Model Name\n");
+
+	// For entries in unit 0 directory.
+
+	// Vendor immediate entry is not found.
+	KUNIT_EXPECT_LT(test, show_immediate(unit0_dev, &config_rom_attributes[0].attr, buf), 0);
+
+	// Model immediate entry is found.
+	KUNIT_EXPECT_GT(test, show_immediate(unit0_dev, &config_rom_attributes[4].attr, buf), 0);
+	KUNIT_EXPECT_STREQ(test, buf, "0xffffff\n");
+
+	// Descriptor leaf entry for vendor is not found.
+	KUNIT_EXPECT_LT(test, show_text_leaf(unit0_dev, &config_rom_attributes[5].attr, buf), 0);
+
+	// Descriptor leaf entry for model is found.
+	KUNIT_EXPECT_GT(test, show_text_leaf(unit0_dev, &config_rom_attributes[6].attr, buf), 0);
+	KUNIT_EXPECT_STREQ(test, buf, "Model Name\n");
+
+	// Specifier_ID immediate entry is found.
+	KUNIT_EXPECT_GT(test, show_immediate(unit0_dev, &config_rom_attributes[2].attr, buf), 0);
+	KUNIT_EXPECT_STREQ(test, buf, "0x00a02d\n");
+
+	// Version immediate entry is found.
+	KUNIT_EXPECT_GT(test, show_immediate(unit0_dev, &config_rom_attributes[3].attr, buf), 0);
+	KUNIT_EXPECT_STREQ(test, buf, "0x010001\n");
+
+	kunit_kfree(test, buf);
+
+	get_modalias_ids(&unit0, ids);
+	KUNIT_EXPECT_MEMEQ(test, ids, unit0_expected_ids, sizeof(ids));
+}
+
+static void device_attr_legacy_avc(struct kunit *test)
+{
+	static const struct fw_device node = {
+		.device = {
+			.type = &fw_device_type,
+		},
+		.config_rom = legacy_avc_config_rom,
+		.config_rom_length = sizeof(legacy_avc_config_rom),
+	};
+	static const struct fw_unit unit0 = {
+		.device = {
+			.type = &fw_unit_type,
+			.parent = (struct device *)&node.device,
+		},
+		.directory = &legacy_avc_config_rom[11],
+	};
+	struct device *node_dev = (struct device *)&node.device;
+	struct device *unit0_dev = (struct device *)&unit0.device;
+	static const int unit0_expected_ids[] = {0x00012345, 0x00fedcba, 0x00abcdef, 0x00543210};
+	char *buf = kunit_kzalloc(test, PAGE_SIZE, GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, buf);
+	int ids[4] = {0, 0, 0, 0};
+
+	// Ensure associations for node and unit devices.
+
+	KUNIT_ASSERT_TRUE(test, is_fw_device(node_dev));
+	KUNIT_ASSERT_FALSE(test, is_fw_unit(node_dev));
+	KUNIT_ASSERT_PTR_EQ(test, fw_device((node_dev)), &node);
+
+	KUNIT_ASSERT_FALSE(test, is_fw_device(unit0_dev));
+	KUNIT_ASSERT_TRUE(test, is_fw_unit(unit0_dev));
+	KUNIT_ASSERT_PTR_EQ(test, fw_parent_device((&unit0)), &node);
+	KUNIT_ASSERT_PTR_EQ(test, fw_unit(unit0_dev), &unit0);
+
+	// For entries in root directory.
+
+	// Vendor immediate entry is found.
+	KUNIT_EXPECT_GT(test, show_immediate(node_dev, &config_rom_attributes[0].attr, buf), 0);
+	KUNIT_EXPECT_STREQ(test, buf, "0x012345\n");
+
+	// Model immediate entry is found.
+	KUNIT_EXPECT_GT(test, show_immediate(node_dev, &config_rom_attributes[4].attr, buf), 0);
+	KUNIT_EXPECT_STREQ(test, buf, "0xfedcba\n");
+
+	// Descriptor leaf entry for vendor is not found.
+	KUNIT_EXPECT_LT(test, show_text_leaf(node_dev, &config_rom_attributes[5].attr, buf), 0);
+
+	// Descriptor leaf entry for model is found.
+	KUNIT_EXPECT_GT(test, show_text_leaf(node_dev, &config_rom_attributes[6].attr, buf), 0);
+	KUNIT_EXPECT_STREQ(test, buf, "ABCDEFGHIJ\n");
+
+	// For entries in unit 0 directory.
+
+	// Vendor immediate entry is not found.
+	KUNIT_EXPECT_LT(test, show_immediate(unit0_dev, &config_rom_attributes[0].attr, buf), 0);
+
+	// Model immediate entry is not found.
+	KUNIT_EXPECT_LT(test, show_immediate(unit0_dev, &config_rom_attributes[4].attr, buf), 0);
+
+	// Descriptor leaf entry for vendor is not found.
+	KUNIT_EXPECT_LT(test, show_text_leaf(unit0_dev, &config_rom_attributes[5].attr, buf), 0);
+
+	// Descriptor leaf entry for model is not found.
+	KUNIT_EXPECT_LT(test, show_text_leaf(unit0_dev, &config_rom_attributes[6].attr, buf), 0);
+
+	// Specifier_ID immediate entry is found.
+	KUNIT_EXPECT_GT(test, show_immediate(unit0_dev, &config_rom_attributes[2].attr, buf), 0);
+	KUNIT_EXPECT_STREQ(test, buf, "0xabcdef\n");
+
+	// Version immediate entry is found.
+	KUNIT_EXPECT_GT(test, show_immediate(unit0_dev, &config_rom_attributes[3].attr, buf), 0);
+	KUNIT_EXPECT_STREQ(test, buf, "0x543210\n");
+
+	kunit_kfree(test, buf);
+
+	get_modalias_ids(&unit0, ids);
+	KUNIT_EXPECT_MEMEQ(test, ids, unit0_expected_ids, sizeof(ids));
+}
+
+static struct kunit_case device_attr_test_cases[] = {
+	KUNIT_CASE(device_attr_simple_avc),
+	KUNIT_CASE(device_attr_legacy_avc),
+	{}
+};
+
+static struct kunit_suite device_attr_test_suite = {
+	.name = "firewire-device-attribute",
+	.test_cases = device_attr_test_cases,
+};
+kunit_test_suite(device_attr_test_suite);