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, 351 insertions, 0 deletions

diff --git a/drivers/misc/eeprom/ee1004.c b/drivers/misc/eeprom/ee1004.c
new file mode 100644
index 000000000..923f404a4
--- /dev/null
+++ b/drivers/misc/eeprom/ee1004.c
@@ -0,0 +1,351 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * ee1004 - driver for DDR4 SPD EEPROMs
+ *
+ * Copyright (C) 2017-2019 Jean Delvare
+ *
+ * Based on the at24 driver:
+ * Copyright (C) 2005-2007 David Brownell
+ * Copyright (C) 2008 Wolfram Sang, Pengutronix
+ */
+
+#include <linux/device.h>
+#include <linux/i2c.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/nvmem-provider.h>
+
+/*
+ * DDR4 memory modules use special EEPROMs following the Jedec EE1004
+ * specification. These are 512-byte EEPROMs using a single I2C address
+ * in the 0x50-0x57 range for data. One of two 256-byte page is selected
+ * by writing a command to I2C address 0x36 or 0x37 on the same I2C bus.
+ *
+ * Therefore we need to request these 2 additional addresses, and serialize
+ * access to all such EEPROMs with a single mutex.
+ *
+ * We assume it is safe to read up to 32 bytes at once from these EEPROMs.
+ * We use SMBus access even if I2C is available, these EEPROMs are small
+ * enough, and reading from them infrequent enough, that we favor simplicity
+ * over performance.
+ */
+
+#define EE1004_MAX_BUSSES		8
+#define EE1004_ADDR_SET_PAGE		0x36
+#define EE1004_NUM_PAGES		2
+#define EE1004_PAGE_SIZE		256
+#define EE1004_PAGE_SHIFT		8
+#define EE1004_EEPROM_SIZE		(EE1004_PAGE_SIZE * EE1004_NUM_PAGES)
+
+/*
+ * Mutex protects ee1004_set_page and ee1004_dev_count, and must be held
+ * from page selection to end of read.
+ */
+static DEFINE_MUTEX(ee1004_bus_lock);
+
+static struct ee1004_bus_data {
+	struct i2c_adapter *adap;
+	struct i2c_client *set_page[EE1004_NUM_PAGES];
+	unsigned int dev_count;
+	int current_page;
+} ee1004_bus_data[EE1004_MAX_BUSSES];
+
+static const struct i2c_device_id ee1004_ids[] = {
+	{ "ee1004" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, ee1004_ids);
+
+/*-------------------------------------------------------------------------*/
+
+static struct ee1004_bus_data *ee1004_get_bus_data(struct i2c_adapter *adap)
+{
+	int i;
+
+	for (i = 0; i < EE1004_MAX_BUSSES; i++)
+		if (ee1004_bus_data[i].adap == adap)
+			return ee1004_bus_data + i;
+
+	/* If not existent yet, create new entry */
+	for (i = 0; i < EE1004_MAX_BUSSES; i++)
+		if (!ee1004_bus_data[i].adap) {
+			ee1004_bus_data[i].adap = adap;
+			return ee1004_bus_data + i;
+		}
+
+	return NULL;
+}
+
+static int ee1004_get_current_page(struct ee1004_bus_data *bd)
+{
+	int err;
+
+	err = i2c_smbus_read_byte(bd->set_page[0]);
+	if (err == -ENXIO) {
+		/* Nack means page 1 is selected */
+		return 1;
+	}
+	if (err < 0) {
+		/* Anything else is a real error, bail out */
+		return err;
+	}
+
+	/* Ack means page 0 is selected, returned value meaningless */
+	return 0;
+}
+
+static int ee1004_set_current_page(struct i2c_client *client, int page)
+{
+	struct ee1004_bus_data *bd = i2c_get_clientdata(client);
+	int ret;
+
+	if (page == bd->current_page)
+		return 0;
+
+	/* Data is ignored */
+	ret = i2c_smbus_write_byte(bd->set_page[page], 0x00);
+	/*
+	 * Don't give up just yet. Some memory modules will select the page
+	 * but not ack the command. Check which page is selected now.
+	 */
+	if (ret == -ENXIO && ee1004_get_current_page(bd) == page)
+		ret = 0;
+	if (ret < 0) {
+		dev_err(&client->dev, "Failed to select page %d (%d)\n", page, ret);
+		return ret;
+	}
+
+	dev_dbg(&client->dev, "Selected page %d\n", page);
+	bd->current_page = page;
+
+	return 0;
+}
+
+static ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf,
+				  unsigned int offset, size_t count)
+{
+	int status, page;
+
+	page = offset >> EE1004_PAGE_SHIFT;
+	offset &= (1 << EE1004_PAGE_SHIFT) - 1;
+
+	status = ee1004_set_current_page(client, page);
+	if (status)
+		return status;
+
+	/* Can't cross page boundaries */
+	if (offset + count > EE1004_PAGE_SIZE)
+		count = EE1004_PAGE_SIZE - offset;
+
+	if (count > I2C_SMBUS_BLOCK_MAX)
+		count = I2C_SMBUS_BLOCK_MAX;
+
+	return i2c_smbus_read_i2c_block_data_or_emulated(client, offset, count, buf);
+}
+
+static int ee1004_read(void *priv, unsigned int off, void *val, size_t count)
+{
+	struct i2c_client *client = priv;
+	char *buf = val;
+	int ret;
+
+	if (unlikely(!count))
+		return count;
+
+	if (off + count > EE1004_EEPROM_SIZE)
+		return -EINVAL;
+
+	/*
+	 * Read data from chip, protecting against concurrent access to
+	 * other EE1004 SPD EEPROMs on the same adapter.
+	 */
+	mutex_lock(&ee1004_bus_lock);
+
+	while (count) {
+		ret = ee1004_eeprom_read(client, buf, off, count);
+		if (ret < 0) {
+			mutex_unlock(&ee1004_bus_lock);
+			return ret;
+		}
+
+		buf += ret;
+		off += ret;
+		count -= ret;
+	}
+
+	mutex_unlock(&ee1004_bus_lock);
+
+	return 0;
+}
+
+static void ee1004_probe_temp_sensor(struct i2c_client *client)
+{
+	struct i2c_board_info info = { .type = "jc42" };
+	unsigned short addr = 0x18 | (client->addr & 7);
+	unsigned short addr_list[] = { addr, I2C_CLIENT_END };
+	u8 data[2];
+	int ret;
+
+	/* byte 14, bit 7 is set if temp sensor is present */
+	ret = ee1004_eeprom_read(client, data, 14, 1);
+	if (ret != 1)
+		return;
+
+	if (!(data[0] & BIT(7))) {
+		/*
+		 * If the SPD data suggests that there is no temperature
+		 * sensor, it may still be there for SPD revision 1.0.
+		 * See SPD Annex L, Revision 1 and 2, for details.
+		 * Check DIMM type and SPD revision; if it is a DDR4
+		 * with SPD revision 1.0, check the thermal sensor address
+		 * and instantiate the jc42 driver if a chip is found at
+		 * that address.
+		 * It is not necessary to check if there is a chip at the
+		 * temperature sensor address since i2c_new_scanned_device()
+		 * will do that and return silently if no chip is found.
+		 */
+		ret = ee1004_eeprom_read(client, data, 1, 2);
+		if (ret != 2 || data[0] != 0x10 || data[1] != 0x0c)
+			return;
+	}
+	i2c_new_scanned_device(client->adapter, &info, addr_list, NULL);
+}
+
+static void ee1004_cleanup(int idx, struct ee1004_bus_data *bd)
+{
+	if (--bd->dev_count == 0) {
+		while (--idx >= 0)
+			i2c_unregister_device(bd->set_page[idx]);
+		memset(bd, 0, sizeof(struct ee1004_bus_data));
+	}
+}
+
+static void ee1004_cleanup_bus_data(void *data)
+{
+	struct ee1004_bus_data *bd = data;
+
+	/* Remove page select clients if this is the last device */
+	mutex_lock(&ee1004_bus_lock);
+	ee1004_cleanup(EE1004_NUM_PAGES, bd);
+	mutex_unlock(&ee1004_bus_lock);
+}
+
+static int ee1004_init_bus_data(struct i2c_client *client)
+{
+	struct ee1004_bus_data *bd;
+	int err, cnr = 0;
+
+	bd = ee1004_get_bus_data(client->adapter);
+	if (!bd)
+		return dev_err_probe(&client->dev, -ENOSPC, "Only %d busses supported",
+				     EE1004_MAX_BUSSES);
+
+	i2c_set_clientdata(client, bd);
+
+	if (++bd->dev_count == 1) {
+		/* Use 2 dummy devices for page select command */
+		for (cnr = 0; cnr < EE1004_NUM_PAGES; cnr++) {
+			struct i2c_client *cl;
+
+			cl = i2c_new_dummy_device(client->adapter, EE1004_ADDR_SET_PAGE + cnr);
+			if (IS_ERR(cl)) {
+				err = PTR_ERR(cl);
+				goto err_out;
+			}
+
+			bd->set_page[cnr] = cl;
+		}
+
+		/* Remember current page to avoid unneeded page select */
+		err = ee1004_get_current_page(bd);
+		if (err < 0)
+			goto err_out;
+
+		dev_dbg(&client->dev, "Currently selected page: %d\n", err);
+		bd->current_page = err;
+	}
+
+	return 0;
+
+err_out:
+	ee1004_cleanup(cnr, bd);
+
+	return err;
+}
+
+static int ee1004_probe(struct i2c_client *client)
+{
+	struct nvmem_config config = {
+		.dev = &client->dev,
+		.name = dev_name(&client->dev),
+		.id = NVMEM_DEVID_NONE,
+		.owner = THIS_MODULE,
+		.type = NVMEM_TYPE_EEPROM,
+		.read_only = true,
+		.root_only = false,
+		.reg_read = ee1004_read,
+		.size = EE1004_EEPROM_SIZE,
+		.word_size = 1,
+		.stride = 1,
+		.priv = client,
+		.compat = true,
+		.base_dev = &client->dev,
+	};
+	struct nvmem_device *ndev;
+	int err;
+
+	/* Make sure we can operate on this adapter */
+	if (!i2c_check_functionality(client->adapter,
+				     I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_I2C_BLOCK) &&
+	    !i2c_check_functionality(client->adapter,
+				     I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_BYTE_DATA))
+		return -EPFNOSUPPORT;
+
+	err = i2c_smbus_read_byte(client);
+	if (err < 0)
+		return -ENODEV;
+
+	mutex_lock(&ee1004_bus_lock);
+
+	err = ee1004_init_bus_data(client);
+	if (err < 0) {
+		mutex_unlock(&ee1004_bus_lock);
+		return err;
+	}
+
+	ee1004_probe_temp_sensor(client);
+
+	mutex_unlock(&ee1004_bus_lock);
+
+	err = devm_add_action_or_reset(&client->dev, ee1004_cleanup_bus_data,
+				       i2c_get_clientdata(client));
+	if (err < 0)
+		return err;
+
+	ndev = devm_nvmem_register(&client->dev, &config);
+	if (IS_ERR(ndev))
+		return PTR_ERR(ndev);
+
+	dev_info(&client->dev,
+		 "%u byte EE1004-compliant SPD EEPROM, read-only\n",
+		 EE1004_EEPROM_SIZE);
+
+	return 0;
+}
+
+/*-------------------------------------------------------------------------*/
+
+static struct i2c_driver ee1004_driver = {
+	.driver = {
+		.name = "ee1004",
+	},
+	.probe = ee1004_probe,
+	.id_table = ee1004_ids,
+};
+module_i2c_driver(ee1004_driver);
+
+MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs");
+MODULE_AUTHOR("Jean Delvare");
+MODULE_LICENSE("GPL");