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, 115 insertions, 0 deletions

diff --git a/sound/soc/sof/nocodec.c b/sound/soc/sof/nocodec.c
new file mode 100644
index 000000000..11a95dba3
--- /dev/null
+++ b/sound/soc/sof/nocodec.c
@@ -0,0 +1,115 @@
+// SPDX-License-Identifier: (GPL-2.0-only OR BSD-3-Clause)
+//
+// This file is provided under a dual BSD/GPLv2 license.  When using or
+// redistributing this file, you may do so under either license.
+//
+// Copyright(c) 2018 Intel Corporation
+//
+// Author: Liam Girdwood <liam.r.girdwood@linux.intel.com>
+//
+
+#include <linux/module.h>
+#include <sound/sof.h>
+#include "sof-audio.h"
+#include "sof-priv.h"
+
+static struct snd_soc_card sof_nocodec_card = {
+	.name = "nocodec", /* the sof- prefix is added by the core */
+	.owner = THIS_MODULE
+};
+
+static int sof_nocodec_bes_setup(struct device *dev,
+				 struct snd_soc_dai_driver *drv,
+				 struct snd_soc_dai_link *links,
+				 int link_num, struct snd_soc_card *card)
+{
+	struct snd_soc_dai_link_component *dlc;
+	int i;
+
+	if (!drv || !links || !card)
+		return -EINVAL;
+
+	/* set up BE dai_links */
+	for (i = 0; i < link_num; i++) {
+		dlc = devm_kcalloc(dev, 2, sizeof(*dlc), GFP_KERNEL);
+		if (!dlc)
+			return -ENOMEM;
+
+		links[i].name = devm_kasprintf(dev, GFP_KERNEL,
+					       "NoCodec-%d", i);
+		if (!links[i].name)
+			return -ENOMEM;
+
+		links[i].stream_name = links[i].name;
+
+		links[i].cpus = &dlc[0];
+		links[i].codecs = &snd_soc_dummy_dlc;
+		links[i].platforms = &dlc[1];
+
+		links[i].num_cpus = 1;
+		links[i].num_codecs = 1;
+		links[i].num_platforms = 1;
+
+		links[i].id = i;
+		links[i].no_pcm = 1;
+		links[i].cpus->dai_name = drv[i].name;
+		links[i].platforms->name = dev_name(dev->parent);
+
+		links[i].playback_only =  drv[i].playback.channels_min && !drv[i].capture.channels_min;
+		links[i].capture_only  = !drv[i].playback.channels_min &&  drv[i].capture.channels_min;
+
+		links[i].be_hw_params_fixup = sof_pcm_dai_link_fixup;
+	}
+
+	card->dai_link = links;
+	card->num_links = link_num;
+
+	return 0;
+}
+
+static int sof_nocodec_setup(struct device *dev,
+			     u32 num_dai_drivers,
+			     struct snd_soc_dai_driver *dai_drivers)
+{
+	struct snd_soc_dai_link *links;
+
+	/* create dummy BE dai_links */
+	links = devm_kcalloc(dev, num_dai_drivers, sizeof(struct snd_soc_dai_link), GFP_KERNEL);
+	if (!links)
+		return -ENOMEM;
+
+	return sof_nocodec_bes_setup(dev, dai_drivers, links, num_dai_drivers, &sof_nocodec_card);
+}
+
+static int sof_nocodec_probe(struct platform_device *pdev)
+{
+	struct snd_soc_card *card = &sof_nocodec_card;
+	struct snd_soc_acpi_mach *mach;
+	int ret;
+
+	card->dev = &pdev->dev;
+	mach = pdev->dev.platform_data;
+
+	snd_soc_card_set_topology_name(card, "sof");
+
+	ret = sof_nocodec_setup(card->dev, mach->mach_params.num_dai_drivers,
+				mach->mach_params.dai_drivers);
+	if (ret < 0)
+		return ret;
+
+	return devm_snd_soc_register_card(&pdev->dev, card);
+}
+
+static struct platform_driver sof_nocodec_audio = {
+	.probe = sof_nocodec_probe,
+	.driver = {
+		.name = "sof-nocodec",
+		.pm = &snd_soc_pm_ops,
+	},
+};
+module_platform_driver(sof_nocodec_audio)
+
+MODULE_LICENSE("Dual BSD/GPL");
+MODULE_DESCRIPTION("ASoC sof nocodec");
+MODULE_AUTHOR("Liam Girdwood");
+MODULE_ALIAS("platform:sof-nocodec");