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, 420 insertions, 0 deletions

diff --git a/drivers/cpufreq/e_powersaver.c b/drivers/cpufreq/e_powersaver.c
new file mode 100644
index 000000000..eb5a9209d
--- /dev/null
+++ b/drivers/cpufreq/e_powersaver.c
@@ -0,0 +1,420 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  Based on documentation provided by Dave Jones. Thanks!
+ *
+ *  BIG FAT DISCLAIMER: Work in progress code. Possibly *dangerous*
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/cpufreq.h>
+#include <linux/ioport.h>
+#include <linux/slab.h>
+#include <linux/timex.h>
+#include <linux/io.h>
+#include <linux/delay.h>
+
+#include <asm/cpu_device_id.h>
+#include <asm/msr.h>
+#include <asm/tsc.h>
+
+#if IS_ENABLED(CONFIG_ACPI_PROCESSOR)
+#include <linux/acpi.h>
+#include <acpi/processor.h>
+#endif
+
+#define EPS_BRAND_C7M	0
+#define EPS_BRAND_C7	1
+#define EPS_BRAND_EDEN	2
+#define EPS_BRAND_C3	3
+#define EPS_BRAND_C7D	4
+
+struct eps_cpu_data {
+	u32 fsb;
+#if IS_ENABLED(CONFIG_ACPI_PROCESSOR)
+	u32 bios_limit;
+#endif
+	struct cpufreq_frequency_table freq_table[];
+};
+
+static struct eps_cpu_data *eps_cpu[NR_CPUS];
+
+/* Module parameters */
+static int freq_failsafe_off;
+static int voltage_failsafe_off;
+static int set_max_voltage;
+
+#if IS_ENABLED(CONFIG_ACPI_PROCESSOR)
+static int ignore_acpi_limit;
+
+static struct acpi_processor_performance *eps_acpi_cpu_perf;
+
+/* Minimum necessary to get acpi_processor_get_bios_limit() working */
+static int eps_acpi_init(void)
+{
+	eps_acpi_cpu_perf = kzalloc_obj(*eps_acpi_cpu_perf);
+	if (!eps_acpi_cpu_perf)
+		return -ENOMEM;
+
+	if (!zalloc_cpumask_var(&eps_acpi_cpu_perf->shared_cpu_map,
+								GFP_KERNEL)) {
+		kfree(eps_acpi_cpu_perf);
+		eps_acpi_cpu_perf = NULL;
+		return -ENOMEM;
+	}
+
+	if (acpi_processor_register_performance(eps_acpi_cpu_perf, 0)) {
+		free_cpumask_var(eps_acpi_cpu_perf->shared_cpu_map);
+		kfree(eps_acpi_cpu_perf);
+		eps_acpi_cpu_perf = NULL;
+		return -EIO;
+	}
+	return 0;
+}
+
+static int eps_acpi_exit(struct cpufreq_policy *policy)
+{
+	if (eps_acpi_cpu_perf) {
+		acpi_processor_unregister_performance(0);
+		free_cpumask_var(eps_acpi_cpu_perf->shared_cpu_map);
+		kfree(eps_acpi_cpu_perf);
+		eps_acpi_cpu_perf = NULL;
+	}
+	return 0;
+}
+#endif
+
+static unsigned int eps_get(unsigned int cpu)
+{
+	struct eps_cpu_data *centaur;
+	u32 lo, hi;
+
+	if (cpu)
+		return 0;
+	centaur = eps_cpu[cpu];
+	if (centaur == NULL)
+		return 0;
+
+	/* Return current frequency */
+	rdmsr(MSR_IA32_PERF_STATUS, lo, hi);
+	return centaur->fsb * ((lo >> 8) & 0xff);
+}
+
+static int eps_set_state(struct eps_cpu_data *centaur,
+			 struct cpufreq_policy *policy,
+			 u32 dest_state)
+{
+	u32 lo, hi;
+	int i;
+
+	/* Wait while CPU is busy */
+	rdmsr(MSR_IA32_PERF_STATUS, lo, hi);
+	i = 0;
+	while (lo & ((1 << 16) | (1 << 17))) {
+		udelay(16);
+		rdmsr(MSR_IA32_PERF_STATUS, lo, hi);
+		i++;
+		if (unlikely(i > 64)) {
+			return -ENODEV;
+		}
+	}
+	/* Set new multiplier and voltage */
+	wrmsr(MSR_IA32_PERF_CTL, dest_state & 0xffff, 0);
+	/* Wait until transition end */
+	i = 0;
+	do {
+		udelay(16);
+		rdmsr(MSR_IA32_PERF_STATUS, lo, hi);
+		i++;
+		if (unlikely(i > 64)) {
+			return -ENODEV;
+		}
+	} while (lo & ((1 << 16) | (1 << 17)));
+
+#ifdef DEBUG
+	{
+	u8 current_multiplier, current_voltage;
+
+	/* Print voltage and multiplier */
+	rdmsr(MSR_IA32_PERF_STATUS, lo, hi);
+	current_voltage = lo & 0xff;
+	pr_info("Current voltage = %dmV\n", current_voltage * 16 + 700);
+	current_multiplier = (lo >> 8) & 0xff;
+	pr_info("Current multiplier = %d\n", current_multiplier);
+	}
+#endif
+	return 0;
+}
+
+static int eps_target(struct cpufreq_policy *policy, unsigned int index)
+{
+	struct eps_cpu_data *centaur;
+	unsigned int cpu = policy->cpu;
+	unsigned int dest_state;
+	int ret;
+
+	if (unlikely(eps_cpu[cpu] == NULL))
+		return -ENODEV;
+	centaur = eps_cpu[cpu];
+
+	/* Make frequency transition */
+	dest_state = centaur->freq_table[index].driver_data & 0xffff;
+	ret = eps_set_state(centaur, policy, dest_state);
+	if (ret)
+		pr_err("Timeout!\n");
+	return ret;
+}
+
+static int eps_cpu_init(struct cpufreq_policy *policy)
+{
+	unsigned int i;
+	u32 lo, hi;
+	u64 val;
+	u8 current_multiplier, current_voltage;
+	u8 max_multiplier, max_voltage;
+	u8 min_multiplier, min_voltage;
+	u8 brand = 0;
+	u32 fsb;
+	struct eps_cpu_data *centaur;
+	struct cpuinfo_x86 *c = &cpu_data(0);
+	struct cpufreq_frequency_table *f_table;
+	int k, step, voltage;
+	int states;
+#if IS_ENABLED(CONFIG_ACPI_PROCESSOR)
+	unsigned int limit;
+#endif
+
+	if (policy->cpu != 0)
+		return -ENODEV;
+
+	/* Check brand */
+	pr_info("Detected VIA ");
+
+	switch (c->x86_model) {
+	case 10:
+		rdmsr(0x1153, lo, hi);
+		brand = (((lo >> 2) ^ lo) >> 18) & 3;
+		pr_cont("Model A ");
+		break;
+	case 13:
+		rdmsr(0x1154, lo, hi);
+		brand = (((lo >> 4) ^ (lo >> 2))) & 0x000000ff;
+		pr_cont("Model D ");
+		break;
+	}
+
+	switch (brand) {
+	case EPS_BRAND_C7M:
+		pr_cont("C7-M\n");
+		break;
+	case EPS_BRAND_C7:
+		pr_cont("C7\n");
+		break;
+	case EPS_BRAND_EDEN:
+		pr_cont("Eden\n");
+		break;
+	case EPS_BRAND_C7D:
+		pr_cont("C7-D\n");
+		break;
+	case EPS_BRAND_C3:
+		pr_cont("C3\n");
+		return -ENODEV;
+	}
+	/* Enable Enhanced PowerSaver */
+	rdmsrq(MSR_IA32_MISC_ENABLE, val);
+	if (!(val & MSR_IA32_MISC_ENABLE_ENHANCED_SPEEDSTEP)) {
+		val |= MSR_IA32_MISC_ENABLE_ENHANCED_SPEEDSTEP;
+		wrmsrq(MSR_IA32_MISC_ENABLE, val);
+		/* Can be locked at 0 */
+		rdmsrq(MSR_IA32_MISC_ENABLE, val);
+		if (!(val & MSR_IA32_MISC_ENABLE_ENHANCED_SPEEDSTEP)) {
+			pr_info("Can't enable Enhanced PowerSaver\n");
+			return -ENODEV;
+		}
+	}
+
+	/* Print voltage and multiplier */
+	rdmsr(MSR_IA32_PERF_STATUS, lo, hi);
+	current_voltage = lo & 0xff;
+	pr_info("Current voltage = %dmV\n", current_voltage * 16 + 700);
+	current_multiplier = (lo >> 8) & 0xff;
+	pr_info("Current multiplier = %d\n", current_multiplier);
+
+	/* Print limits */
+	max_voltage = hi & 0xff;
+	pr_info("Highest voltage = %dmV\n", max_voltage * 16 + 700);
+	max_multiplier = (hi >> 8) & 0xff;
+	pr_info("Highest multiplier = %d\n", max_multiplier);
+	min_voltage = (hi >> 16) & 0xff;
+	pr_info("Lowest voltage = %dmV\n", min_voltage * 16 + 700);
+	min_multiplier = (hi >> 24) & 0xff;
+	pr_info("Lowest multiplier = %d\n", min_multiplier);
+
+	/* Sanity checks */
+	if (current_multiplier == 0 || max_multiplier == 0
+	    || min_multiplier == 0)
+		return -EINVAL;
+	if (current_multiplier > max_multiplier
+	    || max_multiplier <= min_multiplier)
+		return -EINVAL;
+	if (current_voltage > 0x1f || max_voltage > 0x1f)
+		return -EINVAL;
+	if (max_voltage < min_voltage
+	    || current_voltage < min_voltage
+	    || current_voltage > max_voltage)
+		return -EINVAL;
+
+	/* Check for systems using underclocked CPU */
+	if (!freq_failsafe_off && max_multiplier != current_multiplier) {
+		pr_info("Your processor is running at different frequency then its maximum. Aborting.\n");
+		pr_info("You can use freq_failsafe_off option to disable this check.\n");
+		return -EINVAL;
+	}
+	if (!voltage_failsafe_off && max_voltage != current_voltage) {
+		pr_info("Your processor is running at different voltage then its maximum. Aborting.\n");
+		pr_info("You can use voltage_failsafe_off option to disable this check.\n");
+		return -EINVAL;
+	}
+
+	/* Calc FSB speed */
+	fsb = cpu_khz / current_multiplier;
+
+#if IS_ENABLED(CONFIG_ACPI_PROCESSOR)
+	/* Check for ACPI processor speed limit */
+	if (!ignore_acpi_limit && !eps_acpi_init()) {
+		if (!acpi_processor_get_bios_limit(policy->cpu, &limit)) {
+			pr_info("ACPI limit %u.%uGHz\n",
+				limit/1000000,
+				(limit%1000000)/10000);
+			eps_acpi_exit(policy);
+			/* Check if max_multiplier is in BIOS limits */
+			if (limit && max_multiplier * fsb > limit) {
+				pr_info("Aborting\n");
+				return -EINVAL;
+			}
+		}
+	}
+#endif
+
+	/* Allow user to set lower maximum voltage then that reported
+	 * by processor */
+	if (brand == EPS_BRAND_C7M && set_max_voltage) {
+		u32 v;
+
+		/* Change mV to something hardware can use */
+		v = (set_max_voltage - 700) / 16;
+		/* Check if voltage is within limits */
+		if (v >= min_voltage && v <= max_voltage) {
+			pr_info("Setting %dmV as maximum\n", v * 16 + 700);
+			max_voltage = v;
+		}
+	}
+
+	/* Calc number of p-states supported */
+	if (brand == EPS_BRAND_C7M)
+		states = max_multiplier - min_multiplier + 1;
+	else
+		states = 2;
+
+	/* Allocate private data and frequency table for current cpu */
+	centaur = kzalloc_flex(*centaur, freq_table, states + 1);
+	if (!centaur)
+		return -ENOMEM;
+	eps_cpu[0] = centaur;
+
+	/* Copy basic values */
+	centaur->fsb = fsb;
+#if IS_ENABLED(CONFIG_ACPI_PROCESSOR)
+	centaur->bios_limit = limit;
+#endif
+
+	/* Fill frequency and MSR value table */
+	f_table = &centaur->freq_table[0];
+	if (brand != EPS_BRAND_C7M) {
+		f_table[0].frequency = fsb * min_multiplier;
+		f_table[0].driver_data = (min_multiplier << 8) | min_voltage;
+		f_table[1].frequency = fsb * max_multiplier;
+		f_table[1].driver_data = (max_multiplier << 8) | max_voltage;
+		f_table[2].frequency = CPUFREQ_TABLE_END;
+	} else {
+		k = 0;
+		step = ((max_voltage - min_voltage) * 256)
+			/ (max_multiplier - min_multiplier);
+		for (i = min_multiplier; i <= max_multiplier; i++) {
+			voltage = (k * step) / 256 + min_voltage;
+			f_table[k].frequency = fsb * i;
+			f_table[k].driver_data = (i << 8) | voltage;
+			k++;
+		}
+		f_table[k].frequency = CPUFREQ_TABLE_END;
+	}
+
+	policy->cpuinfo.transition_latency = 140000; /* 844mV -> 700mV in ns */
+	policy->freq_table = &centaur->freq_table[0];
+
+	return 0;
+}
+
+static void eps_cpu_exit(struct cpufreq_policy *policy)
+{
+	unsigned int cpu = policy->cpu;
+
+	/* Bye */
+	kfree(eps_cpu[cpu]);
+	eps_cpu[cpu] = NULL;
+}
+
+static struct cpufreq_driver eps_driver = {
+	.verify		= cpufreq_generic_frequency_table_verify,
+	.target_index	= eps_target,
+	.init		= eps_cpu_init,
+	.exit		= eps_cpu_exit,
+	.get		= eps_get,
+	.name		= "e_powersaver",
+};
+
+
+/* This driver will work only on Centaur C7 processors with
+ * Enhanced SpeedStep/PowerSaver registers */
+static const struct x86_cpu_id eps_cpu_id[] = {
+	X86_MATCH_VENDOR_FAM_FEATURE(CENTAUR, 6, X86_FEATURE_EST, NULL),
+	{}
+};
+MODULE_DEVICE_TABLE(x86cpu, eps_cpu_id);
+
+static int __init eps_init(void)
+{
+	if (!x86_match_cpu(eps_cpu_id) || boot_cpu_data.x86_model < 10)
+		return -ENODEV;
+	if (cpufreq_register_driver(&eps_driver))
+		return -EINVAL;
+	return 0;
+}
+
+static void __exit eps_exit(void)
+{
+	cpufreq_unregister_driver(&eps_driver);
+}
+
+/* Allow user to overclock his machine or to change frequency to higher after
+ * unloading module */
+module_param(freq_failsafe_off, int, 0644);
+MODULE_PARM_DESC(freq_failsafe_off, "Disable current vs max frequency check");
+module_param(voltage_failsafe_off, int, 0644);
+MODULE_PARM_DESC(voltage_failsafe_off, "Disable current vs max voltage check");
+#if IS_ENABLED(CONFIG_ACPI_PROCESSOR)
+module_param(ignore_acpi_limit, int, 0644);
+MODULE_PARM_DESC(ignore_acpi_limit, "Don't check ACPI's processor speed limit");
+#endif
+module_param(set_max_voltage, int, 0644);
+MODULE_PARM_DESC(set_max_voltage, "Set maximum CPU voltage (mV) C7-M only");
+
+MODULE_AUTHOR("Rafal Bilski <rafalbilski@interia.pl>");
+MODULE_DESCRIPTION("Enhanced PowerSaver driver for VIA C7 CPU's.");
+MODULE_LICENSE("GPL");
+
+module_init(eps_init);
+module_exit(eps_exit);