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, 273 insertions, 0 deletions

diff --git a/drivers/cpufreq/pasemi-cpufreq.c b/drivers/cpufreq/pasemi-cpufreq.c
new file mode 100644
index 000000000..a39313493
--- /dev/null
+++ b/drivers/cpufreq/pasemi-cpufreq.c
@@ -0,0 +1,273 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2007 PA Semi, Inc
+ *
+ * Authors: Egor Martovetsky <egor@pasemi.com>
+ *	    Olof Johansson <olof@lixom.net>
+ *
+ * Maintained by: Olof Johansson <olof@lixom.net>
+ *
+ * Based on arch/powerpc/platforms/cell/cbe_cpufreq.c:
+ * (C) Copyright IBM Deutschland Entwicklung GmbH 2005
+ */
+
+#include <linux/cpufreq.h>
+#include <linux/timer.h>
+#include <linux/module.h>
+#include <linux/of_address.h>
+
+#include <asm/hw_irq.h>
+#include <asm/io.h>
+#include <asm/time.h>
+#include <asm/smp.h>
+
+#include <platforms/pasemi/pasemi.h>
+
+#define SDCASR_REG		0x0100
+#define SDCASR_REG_STRIDE	0x1000
+#define SDCPWR_CFGA0_REG	0x0100
+#define SDCPWR_PWST0_REG	0x0000
+#define SDCPWR_GIZTIME_REG	0x0440
+
+/* SDCPWR_GIZTIME_REG fields */
+#define SDCPWR_GIZTIME_GR	0x80000000
+#define SDCPWR_GIZTIME_LONGLOCK	0x000000ff
+
+/* Offset of ASR registers from SDC base */
+#define SDCASR_OFFSET		0x120000
+
+static void __iomem *sdcpwr_mapbase;
+static void __iomem *sdcasr_mapbase;
+
+/* Current astate, is used when waking up from power savings on
+ * one core, in case the other core has switched states during
+ * the idle time.
+ */
+static int current_astate;
+
+/* We support 5(A0-A4) power states excluding turbo(A5-A6) modes */
+static struct cpufreq_frequency_table pas_freqs[] = {
+	{0, 0,	0},
+	{0, 1,	0},
+	{0, 2,	0},
+	{0, 3,	0},
+	{0, 4,	0},
+	{0, 0,	CPUFREQ_TABLE_END},
+};
+
+/*
+ * hardware specific functions
+ */
+
+static int get_astate_freq(int astate)
+{
+	u32 ret;
+	ret = in_le32(sdcpwr_mapbase + SDCPWR_CFGA0_REG + (astate * 0x10));
+
+	return ret & 0x3f;
+}
+
+static int get_cur_astate(int cpu)
+{
+	u32 ret;
+
+	ret = in_le32(sdcpwr_mapbase + SDCPWR_PWST0_REG);
+	ret = (ret >> (cpu * 4)) & 0x7;
+
+	return ret;
+}
+
+static int get_gizmo_latency(void)
+{
+	u32 giztime, ret;
+
+	giztime = in_le32(sdcpwr_mapbase + SDCPWR_GIZTIME_REG);
+
+	/* just provide the upper bound */
+	if (giztime & SDCPWR_GIZTIME_GR)
+		ret = (giztime & SDCPWR_GIZTIME_LONGLOCK) * 128000;
+	else
+		ret = (giztime & SDCPWR_GIZTIME_LONGLOCK) * 1000;
+
+	return ret;
+}
+
+static void set_astate(int cpu, unsigned int astate)
+{
+	unsigned long flags;
+
+	/* Return if called before init has run */
+	if (unlikely(!sdcasr_mapbase))
+		return;
+
+	local_irq_save(flags);
+
+	out_le32(sdcasr_mapbase + SDCASR_REG + SDCASR_REG_STRIDE*cpu, astate);
+
+	local_irq_restore(flags);
+}
+
+int check_astate(void)
+{
+	return get_cur_astate(hard_smp_processor_id());
+}
+
+void restore_astate(int cpu)
+{
+	set_astate(cpu, current_astate);
+}
+
+/*
+ * cpufreq functions
+ */
+
+static int pas_cpufreq_cpu_init(struct cpufreq_policy *policy)
+{
+	struct cpufreq_frequency_table *pos;
+	const u32 *max_freqp;
+	u32 max_freq;
+	int cur_astate, idx;
+	struct resource res;
+	struct device_node *cpu, *dn;
+	int err = -ENODEV;
+
+	cpu = of_get_cpu_node(policy->cpu, NULL);
+	if (!cpu)
+		goto out;
+
+	max_freqp = of_get_property(cpu, "clock-frequency", NULL);
+	of_node_put(cpu);
+	if (!max_freqp) {
+		err = -EINVAL;
+		goto out;
+	}
+
+	/* we need the freq in kHz */
+	max_freq = *max_freqp / 1000;
+
+	dn = of_find_compatible_node(NULL, NULL, "1682m-sdc");
+	if (!dn)
+		dn = of_find_compatible_node(NULL, NULL,
+					     "pasemi,pwrficient-sdc");
+	if (!dn)
+		goto out;
+	err = of_address_to_resource(dn, 0, &res);
+	of_node_put(dn);
+	if (err)
+		goto out;
+	sdcasr_mapbase = ioremap(res.start + SDCASR_OFFSET, 0x2000);
+	if (!sdcasr_mapbase) {
+		err = -EINVAL;
+		goto out;
+	}
+
+	dn = of_find_compatible_node(NULL, NULL, "1682m-gizmo");
+	if (!dn)
+		dn = of_find_compatible_node(NULL, NULL,
+					     "pasemi,pwrficient-gizmo");
+	if (!dn) {
+		err = -ENODEV;
+		goto out_unmap_sdcasr;
+	}
+	err = of_address_to_resource(dn, 0, &res);
+	of_node_put(dn);
+	if (err)
+		goto out_unmap_sdcasr;
+	sdcpwr_mapbase = ioremap(res.start, 0x1000);
+	if (!sdcpwr_mapbase) {
+		err = -EINVAL;
+		goto out_unmap_sdcasr;
+	}
+
+	pr_debug("init cpufreq on CPU %d\n", policy->cpu);
+	pr_debug("max clock-frequency is at %u kHz\n", max_freq);
+	pr_debug("initializing frequency table\n");
+
+	/* initialize frequency table */
+	cpufreq_for_each_entry_idx(pos, pas_freqs, idx) {
+		pos->frequency = get_astate_freq(pos->driver_data) * 100000;
+		pr_debug("%d: %d\n", idx, pos->frequency);
+	}
+
+	cur_astate = get_cur_astate(policy->cpu);
+	pr_debug("current astate is at %d\n",cur_astate);
+
+	policy->cur = pas_freqs[cur_astate].frequency;
+	ppc_proc_freq = policy->cur * 1000ul;
+
+	cpufreq_generic_init(policy, pas_freqs, get_gizmo_latency());
+	return 0;
+
+out_unmap_sdcasr:
+	iounmap(sdcasr_mapbase);
+out:
+	return err;
+}
+
+static void pas_cpufreq_cpu_exit(struct cpufreq_policy *policy)
+{
+	/*
+	 * We don't support CPU hotplug. Don't unmap after the system
+	 * has already made it to a running state.
+	 */
+	if (system_state >= SYSTEM_RUNNING)
+		return;
+
+	if (sdcasr_mapbase)
+		iounmap(sdcasr_mapbase);
+	if (sdcpwr_mapbase)
+		iounmap(sdcpwr_mapbase);
+}
+
+static int pas_cpufreq_target(struct cpufreq_policy *policy,
+			      unsigned int pas_astate_new)
+{
+	int i;
+
+	pr_debug("setting frequency for cpu %d to %d kHz, 1/%d of max frequency\n",
+		 policy->cpu,
+		 pas_freqs[pas_astate_new].frequency,
+		 pas_freqs[pas_astate_new].driver_data);
+
+	current_astate = pas_astate_new;
+
+	for_each_online_cpu(i)
+		set_astate(i, pas_astate_new);
+
+	ppc_proc_freq = pas_freqs[pas_astate_new].frequency * 1000ul;
+	return 0;
+}
+
+static struct cpufreq_driver pas_cpufreq_driver = {
+	.name		= "pas-cpufreq",
+	.flags		= CPUFREQ_CONST_LOOPS,
+	.init		= pas_cpufreq_cpu_init,
+	.exit		= pas_cpufreq_cpu_exit,
+	.verify		= cpufreq_generic_frequency_table_verify,
+	.target_index	= pas_cpufreq_target,
+};
+
+/*
+ * module init and destoy
+ */
+
+static int __init pas_cpufreq_init(void)
+{
+	if (!of_machine_is_compatible("PA6T-1682M") &&
+	    !of_machine_is_compatible("pasemi,pwrficient"))
+		return -ENODEV;
+
+	return cpufreq_register_driver(&pas_cpufreq_driver);
+}
+
+static void __exit pas_cpufreq_exit(void)
+{
+	cpufreq_unregister_driver(&pas_cpufreq_driver);
+}
+
+module_init(pas_cpufreq_init);
+module_exit(pas_cpufreq_exit);
+
+MODULE_DESCRIPTION("cpufreq driver for PA Semi PWRficient");
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Egor Martovetsky <egor@pasemi.com>, Olof Johansson <olof@lixom.net>");