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, 130 insertions, 0 deletions

diff --git a/drivers/ssb/pcihost_wrapper.c b/drivers/ssb/pcihost_wrapper.c
new file mode 100644
index 000000000..5b6b5e0e4
--- /dev/null
+++ b/drivers/ssb/pcihost_wrapper.c
@@ -0,0 +1,130 @@
+/*
+ * Sonics Silicon Backplane
+ * PCI Hostdevice wrapper
+ *
+ * Copyright (c) 2005 Martin Langer <martin-langer@gmx.de>
+ * Copyright (c) 2005 Stefano Brivio <st3@riseup.net>
+ * Copyright (c) 2005 Danny van Dyk <kugelfang@gentoo.org>
+ * Copyright (c) 2005 Andreas Jaggi <andreas.jaggi@waterwave.ch>
+ * Copyright (c) 2005-2007 Michael Buesch <m@bues.ch>
+ *
+ * Licensed under the GNU/GPL. See COPYING for details.
+ */
+
+#include <linux/pm.h>
+#include <linux/pci.h>
+#include <linux/export.h>
+#include <linux/slab.h>
+#include <linux/ssb/ssb.h>
+
+
+#ifdef CONFIG_PM_SLEEP
+static int ssb_pcihost_suspend(struct device *d)
+{
+	struct pci_dev *dev = to_pci_dev(d);
+	struct ssb_bus *ssb = pci_get_drvdata(dev);
+	int err;
+
+	err = ssb_bus_suspend(ssb);
+	if (err)
+		return err;
+	pci_save_state(dev);
+	pci_disable_device(dev);
+
+	/* if there is a wakeup enabled child device on ssb bus,
+	   enable pci wakeup posibility. */
+	device_set_wakeup_enable(d, d->power.wakeup_path);
+
+	pci_prepare_to_sleep(dev);
+
+	return 0;
+}
+
+static int ssb_pcihost_resume(struct device *d)
+{
+	struct pci_dev *dev = to_pci_dev(d);
+	struct ssb_bus *ssb = pci_get_drvdata(dev);
+	int err;
+
+	pci_back_from_sleep(dev);
+	err = pci_enable_device(dev);
+	if (err)
+		return err;
+	pci_restore_state(dev);
+	err = ssb_bus_resume(ssb);
+	if (err)
+		return err;
+
+	return 0;
+}
+
+static const struct dev_pm_ops ssb_pcihost_pm_ops = {
+	SET_SYSTEM_SLEEP_PM_OPS(ssb_pcihost_suspend, ssb_pcihost_resume)
+};
+
+#endif /* CONFIG_PM_SLEEP */
+
+static int ssb_pcihost_probe(struct pci_dev *dev,
+			     const struct pci_device_id *id)
+{
+	struct ssb_bus *ssb;
+	int err = -ENOMEM;
+	u32 val;
+
+	ssb = kzalloc_obj(*ssb);
+	if (!ssb)
+		goto out;
+	err = pci_enable_device(dev);
+	if (err)
+		goto err_kfree_ssb;
+	err = pci_request_regions(dev, dev_driver_string(&dev->dev));
+	if (err)
+		goto err_pci_disable;
+	pci_set_master(dev);
+
+	/* Disable the RETRY_TIMEOUT register (0x41) to keep
+	 * PCI Tx retries from interfering with C3 CPU state */
+	pci_read_config_dword(dev, 0x40, &val);
+	if ((val & 0x0000ff00) != 0)
+		pci_write_config_dword(dev, 0x40, val & 0xffff00ff);
+
+	err = ssb_bus_pcibus_register(ssb, dev);
+	if (err)
+		goto err_pci_release_regions;
+
+	pci_set_drvdata(dev, ssb);
+
+out:
+	return err;
+
+err_pci_release_regions:
+	pci_release_regions(dev);
+err_pci_disable:
+	pci_disable_device(dev);
+err_kfree_ssb:
+	kfree(ssb);
+	return err;
+}
+
+static void ssb_pcihost_remove(struct pci_dev *dev)
+{
+	struct ssb_bus *ssb = pci_get_drvdata(dev);
+
+	ssb_bus_unregister(ssb);
+	pci_release_regions(dev);
+	pci_disable_device(dev);
+	kfree(ssb);
+	pci_set_drvdata(dev, NULL);
+}
+
+int ssb_pcihost_register(struct pci_driver *driver)
+{
+	driver->probe = ssb_pcihost_probe;
+	driver->remove = ssb_pcihost_remove;
+#ifdef CONFIG_PM_SLEEP
+	driver->driver.pm = &ssb_pcihost_pm_ops;
+#endif
+
+	return pci_register_driver(driver);
+}
+EXPORT_SYMBOL(ssb_pcihost_register);