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, 131 insertions, 0 deletions

diff --git a/drivers/comedi/range.c b/drivers/comedi/range.c
new file mode 100644
index 000000000..5b8f66236
--- /dev/null
+++ b/drivers/comedi/range.c
@@ -0,0 +1,131 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * comedi/range.c
+ * comedi routines for voltage ranges
+ *
+ * COMEDI - Linux Control and Measurement Device Interface
+ * Copyright (C) 1997-8 David A. Schleef <ds@schleef.org>
+ */
+
+#include <linux/uaccess.h>
+#include <linux/comedi/comedidev.h>
+#include "comedi_internal.h"
+
+const struct comedi_lrange range_bipolar10 = { 1, {BIP_RANGE(10)} };
+EXPORT_SYMBOL_GPL(range_bipolar10);
+const struct comedi_lrange range_bipolar5 = { 1, {BIP_RANGE(5)} };
+EXPORT_SYMBOL_GPL(range_bipolar5);
+const struct comedi_lrange range_bipolar2_5 = { 1, {BIP_RANGE(2.5)} };
+EXPORT_SYMBOL_GPL(range_bipolar2_5);
+const struct comedi_lrange range_unipolar10 = { 1, {UNI_RANGE(10)} };
+EXPORT_SYMBOL_GPL(range_unipolar10);
+const struct comedi_lrange range_unipolar5 = { 1, {UNI_RANGE(5)} };
+EXPORT_SYMBOL_GPL(range_unipolar5);
+const struct comedi_lrange range_unipolar2_5 = { 1, {UNI_RANGE(2.5)} };
+EXPORT_SYMBOL_GPL(range_unipolar2_5);
+const struct comedi_lrange range_0_20mA = { 1, {RANGE_mA(0, 20)} };
+EXPORT_SYMBOL_GPL(range_0_20mA);
+const struct comedi_lrange range_4_20mA = { 1, {RANGE_mA(4, 20)} };
+EXPORT_SYMBOL_GPL(range_4_20mA);
+const struct comedi_lrange range_0_32mA = { 1, {RANGE_mA(0, 32)} };
+EXPORT_SYMBOL_GPL(range_0_32mA);
+const struct comedi_lrange range_unknown = { 1, {{0, 1000000, UNIT_none} } };
+EXPORT_SYMBOL_GPL(range_unknown);
+
+/*
+ * COMEDI_RANGEINFO ioctl
+ * range information
+ *
+ * arg:
+ *	pointer to comedi_rangeinfo structure
+ *
+ * reads:
+ *	comedi_rangeinfo structure
+ *
+ * writes:
+ *	array of comedi_krange structures to rangeinfo->range_ptr pointer
+ */
+int do_rangeinfo_ioctl(struct comedi_device *dev,
+		       struct comedi_rangeinfo *it)
+{
+	int subd, chan;
+	const struct comedi_lrange *lr;
+	struct comedi_subdevice *s;
+
+	subd = (it->range_type >> 24) & 0xff;
+	chan = (it->range_type >> 16) & 0xff;
+
+	if (!dev->attached)
+		return -EINVAL;
+	if (subd >= dev->n_subdevices)
+		return -EINVAL;
+	s = &dev->subdevices[subd];
+	if (s->range_table) {
+		lr = s->range_table;
+	} else if (s->range_table_list) {
+		if (chan >= s->n_chan)
+			return -EINVAL;
+		lr = s->range_table_list[chan];
+	} else {
+		return -EINVAL;
+	}
+
+	if (RANGE_LENGTH(it->range_type) != lr->length) {
+		dev_dbg(dev->class_dev,
+			"wrong length %d should be %d (0x%08x)\n",
+			RANGE_LENGTH(it->range_type),
+			lr->length, it->range_type);
+		return -EINVAL;
+	}
+
+	if (copy_to_user(it->range_ptr, lr->range,
+			 sizeof(struct comedi_krange) * lr->length))
+		return -EFAULT;
+
+	return 0;
+}
+
+/**
+ * comedi_check_chanlist() - Validate each element in a chanlist.
+ * @s: comedi_subdevice struct
+ * @n: number of elements in the chanlist
+ * @chanlist: the chanlist to validate
+ *
+ * Each element consists of a channel number, a range index, an analog
+ * reference type and some flags, all packed into an unsigned int.
+ *
+ * This checks that the channel number and range index are supported by
+ * the comedi subdevice.  It does not check whether the analog reference
+ * type and the flags are supported.  Drivers that care should check those
+ * themselves.
+ *
+ * Return: %0 if all @chanlist elements are valid (success),
+ *         %-EINVAL if one or more elements are invalid.
+ */
+int comedi_check_chanlist(struct comedi_subdevice *s, int n,
+			  unsigned int *chanlist)
+{
+	struct comedi_device *dev = s->device;
+	unsigned int chanspec;
+	int chan, range_len, i;
+
+	for (i = 0; i < n; i++) {
+		chanspec = chanlist[i];
+		chan = CR_CHAN(chanspec);
+		if (s->range_table)
+			range_len = s->range_table->length;
+		else if (s->range_table_list && chan < s->n_chan)
+			range_len = s->range_table_list[chan]->length;
+		else
+			range_len = 0;
+		if (chan >= s->n_chan ||
+		    CR_RANGE(chanspec) >= range_len) {
+			dev_warn(dev->class_dev,
+				 "bad chanlist[%d]=0x%08x chan=%d range length=%d\n",
+				 i, chanspec, chan, range_len);
+			return -EINVAL;
+		}
+	}
+	return 0;
+}
+EXPORT_SYMBOL_GPL(comedi_check_chanlist);