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, 318 insertions, 0 deletions

diff --git a/drivers/cpufreq/longrun.c b/drivers/cpufreq/longrun.c
new file mode 100644
index 000000000..f3aaca049
--- /dev/null
+++ b/drivers/cpufreq/longrun.c
@@ -0,0 +1,318 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * (C) 2002 - 2003  Dominik Brodowski <linux@brodo.de>
+ *
+ *  BIG FAT DISCLAIMER: Work in progress code. Possibly *dangerous*
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/cpufreq.h>
+#include <linux/timex.h>
+
+#include <asm/msr.h>
+#include <asm/processor.h>
+#include <asm/cpu_device_id.h>
+#include <asm/cpuid/api.h>
+
+static struct cpufreq_driver	longrun_driver;
+
+/**
+ * longrun_{low,high}_freq is needed for the conversion of cpufreq kHz
+ * values into per cent values. In TMTA microcode, the following is valid:
+ * performance_pctg = (current_freq - low_freq)/(high_freq - low_freq)
+ */
+static unsigned int longrun_low_freq, longrun_high_freq;
+
+
+/**
+ * longrun_get_policy - get the current LongRun policy
+ * @policy: struct cpufreq_policy where current policy is written into
+ *
+ * Reads the current LongRun policy by access to MSR_TMTA_LONGRUN_FLAGS
+ * and MSR_TMTA_LONGRUN_CTRL
+ */
+static void longrun_get_policy(struct cpufreq_policy *policy)
+{
+	u32 msr_lo, msr_hi;
+
+	rdmsr(MSR_TMTA_LONGRUN_FLAGS, msr_lo, msr_hi);
+	pr_debug("longrun flags are %x - %x\n", msr_lo, msr_hi);
+	if (msr_lo & 0x01)
+		policy->policy = CPUFREQ_POLICY_PERFORMANCE;
+	else
+		policy->policy = CPUFREQ_POLICY_POWERSAVE;
+
+	rdmsr(MSR_TMTA_LONGRUN_CTRL, msr_lo, msr_hi);
+	pr_debug("longrun ctrl is %x - %x\n", msr_lo, msr_hi);
+	msr_lo &= 0x0000007F;
+	msr_hi &= 0x0000007F;
+
+	if (longrun_high_freq <= longrun_low_freq) {
+		/* Assume degenerate Longrun table */
+		policy->min = policy->max = longrun_high_freq;
+	} else {
+		policy->min = longrun_low_freq + msr_lo *
+			((longrun_high_freq - longrun_low_freq) / 100);
+		policy->max = longrun_low_freq + msr_hi *
+			((longrun_high_freq - longrun_low_freq) / 100);
+	}
+	policy->cpu = 0;
+}
+
+
+/**
+ * longrun_set_policy - sets a new CPUFreq policy
+ * @policy: new policy
+ *
+ * Sets a new CPUFreq policy on LongRun-capable processors. This function
+ * has to be called with cpufreq_driver locked.
+ */
+static int longrun_set_policy(struct cpufreq_policy *policy)
+{
+	u32 msr_lo, msr_hi;
+	u32 pctg_lo, pctg_hi;
+
+	if (!policy)
+		return -EINVAL;
+
+	if (longrun_high_freq <= longrun_low_freq) {
+		/* Assume degenerate Longrun table */
+		pctg_lo = pctg_hi = 100;
+	} else {
+		pctg_lo = (policy->min - longrun_low_freq) /
+			((longrun_high_freq - longrun_low_freq) / 100);
+		pctg_hi = (policy->max - longrun_low_freq) /
+			((longrun_high_freq - longrun_low_freq) / 100);
+	}
+
+	if (pctg_hi > 100)
+		pctg_hi = 100;
+	if (pctg_lo > pctg_hi)
+		pctg_lo = pctg_hi;
+
+	/* performance or economy mode */
+	rdmsr(MSR_TMTA_LONGRUN_FLAGS, msr_lo, msr_hi);
+	msr_lo &= 0xFFFFFFFE;
+	switch (policy->policy) {
+	case CPUFREQ_POLICY_PERFORMANCE:
+		msr_lo |= 0x00000001;
+		break;
+	case CPUFREQ_POLICY_POWERSAVE:
+		break;
+	}
+	wrmsr(MSR_TMTA_LONGRUN_FLAGS, msr_lo, msr_hi);
+
+	/* lower and upper boundary */
+	rdmsr(MSR_TMTA_LONGRUN_CTRL, msr_lo, msr_hi);
+	msr_lo &= 0xFFFFFF80;
+	msr_hi &= 0xFFFFFF80;
+	msr_lo |= pctg_lo;
+	msr_hi |= pctg_hi;
+	wrmsr(MSR_TMTA_LONGRUN_CTRL, msr_lo, msr_hi);
+
+	return 0;
+}
+
+
+/**
+ * longrun_verify_poliy - verifies a new CPUFreq policy
+ * @policy: the policy to verify
+ *
+ * Validates a new CPUFreq policy. This function has to be called with
+ * cpufreq_driver locked.
+ */
+static int longrun_verify_policy(struct cpufreq_policy_data *policy)
+{
+	if (!policy)
+		return -EINVAL;
+
+	policy->cpu = 0;
+	cpufreq_verify_within_cpu_limits(policy);
+
+	return 0;
+}
+
+static unsigned int longrun_get(unsigned int cpu)
+{
+	u32 eax, ebx, ecx, edx;
+
+	if (cpu)
+		return 0;
+
+	cpuid(0x80860007, &eax, &ebx, &ecx, &edx);
+	pr_debug("cpuid eax is %u\n", eax);
+
+	return eax * 1000;
+}
+
+/**
+ * longrun_determine_freqs - determines the lowest and highest possible core frequency
+ * @low_freq: an int to put the lowest frequency into
+ * @high_freq: an int to put the highest frequency into
+ *
+ * Determines the lowest and highest possible core frequencies on this CPU.
+ * This is necessary to calculate the performance percentage according to
+ * TMTA rules:
+ * performance_pctg = (target_freq - low_freq)/(high_freq - low_freq)
+ */
+static int longrun_determine_freqs(unsigned int *low_freq,
+						      unsigned int *high_freq)
+{
+	u32 msr_lo, msr_hi;
+	u32 save_lo, save_hi;
+	u32 eax, ebx, ecx, edx;
+	u32 try_hi;
+	struct cpuinfo_x86 *c = &cpu_data(0);
+
+	if (!low_freq || !high_freq)
+		return -EINVAL;
+
+	if (cpu_has(c, X86_FEATURE_LRTI)) {
+		/* if the LongRun Table Interface is present, the
+		 * detection is a bit easier:
+		 * For minimum frequency, read out the maximum
+		 * level (msr_hi), write that into "currently
+		 * selected level", and read out the frequency.
+		 * For maximum frequency, read out level zero.
+		 */
+		/* minimum */
+		rdmsr(MSR_TMTA_LRTI_READOUT, msr_lo, msr_hi);
+		wrmsr(MSR_TMTA_LRTI_READOUT, msr_hi, msr_hi);
+		rdmsr(MSR_TMTA_LRTI_VOLT_MHZ, msr_lo, msr_hi);
+		*low_freq = msr_lo * 1000; /* to kHz */
+
+		/* maximum */
+		wrmsr(MSR_TMTA_LRTI_READOUT, 0, msr_hi);
+		rdmsr(MSR_TMTA_LRTI_VOLT_MHZ, msr_lo, msr_hi);
+		*high_freq = msr_lo * 1000; /* to kHz */
+
+		pr_debug("longrun table interface told %u - %u kHz\n",
+				*low_freq, *high_freq);
+
+		if (*low_freq > *high_freq)
+			*low_freq = *high_freq;
+		return 0;
+	}
+
+	/* set the upper border to the value determined during TSC init */
+	*high_freq = (cpu_khz / 1000);
+	*high_freq = *high_freq * 1000;
+	pr_debug("high frequency is %u kHz\n", *high_freq);
+
+	/* get current borders */
+	rdmsr(MSR_TMTA_LONGRUN_CTRL, msr_lo, msr_hi);
+	save_lo = msr_lo & 0x0000007F;
+	save_hi = msr_hi & 0x0000007F;
+
+	/* if current perf_pctg is larger than 90%, we need to decrease the
+	 * upper limit to make the calculation more accurate.
+	 */
+	cpuid(0x80860007, &eax, &ebx, &ecx, &edx);
+	/* try decreasing in 10% steps, some processors react only
+	 * on some barrier values */
+	for (try_hi = 80; try_hi > 0 && ecx > 90; try_hi -= 10) {
+		/* set to 0 to try_hi perf_pctg */
+		msr_lo &= 0xFFFFFF80;
+		msr_hi &= 0xFFFFFF80;
+		msr_hi |= try_hi;
+		wrmsr(MSR_TMTA_LONGRUN_CTRL, msr_lo, msr_hi);
+
+		/* read out current core MHz and current perf_pctg */
+		cpuid(0x80860007, &eax, &ebx, &ecx, &edx);
+
+		/* restore values */
+		wrmsr(MSR_TMTA_LONGRUN_CTRL, save_lo, save_hi);
+	}
+	pr_debug("percentage is %u %%, freq is %u MHz\n", ecx, eax);
+
+	/* performance_pctg = (current_freq - low_freq)/(high_freq - low_freq)
+	 * eqals
+	 * low_freq * (1 - perf_pctg) = (cur_freq - high_freq * perf_pctg)
+	 *
+	 * high_freq * perf_pctg is stored tempoarily into "ebx".
+	 */
+	ebx = (((cpu_khz / 1000) * ecx) / 100); /* to MHz */
+
+	if ((ecx > 95) || (ecx == 0) || (eax < ebx))
+		return -EIO;
+
+	edx = ((eax - ebx) * 100) / (100 - ecx);
+	*low_freq = edx * 1000; /* back to kHz */
+
+	pr_debug("low frequency is %u kHz\n", *low_freq);
+
+	if (*low_freq > *high_freq)
+		*low_freq = *high_freq;
+
+	return 0;
+}
+
+
+static int longrun_cpu_init(struct cpufreq_policy *policy)
+{
+	int result = 0;
+
+	/* capability check */
+	if (policy->cpu != 0)
+		return -ENODEV;
+
+	/* detect low and high frequency */
+	result = longrun_determine_freqs(&longrun_low_freq, &longrun_high_freq);
+	if (result)
+		return result;
+
+	/* cpuinfo and default policy values */
+	policy->cpuinfo.min_freq = longrun_low_freq;
+	policy->cpuinfo.max_freq = longrun_high_freq;
+	longrun_get_policy(policy);
+
+	return 0;
+}
+
+
+static struct cpufreq_driver longrun_driver = {
+	.flags		= CPUFREQ_CONST_LOOPS,
+	.verify		= longrun_verify_policy,
+	.setpolicy	= longrun_set_policy,
+	.get		= longrun_get,
+	.init		= longrun_cpu_init,
+	.name		= "longrun",
+};
+
+static const struct x86_cpu_id longrun_ids[] = {
+	X86_MATCH_VENDOR_FEATURE(TRANSMETA, X86_FEATURE_LONGRUN, NULL),
+	{}
+};
+MODULE_DEVICE_TABLE(x86cpu, longrun_ids);
+
+/**
+ * longrun_init - initializes the Transmeta Crusoe LongRun CPUFreq driver
+ *
+ * Initializes the LongRun support.
+ */
+static int __init longrun_init(void)
+{
+	if (!x86_match_cpu(longrun_ids))
+		return -ENODEV;
+	return cpufreq_register_driver(&longrun_driver);
+}
+
+
+/**
+ * longrun_exit - unregisters LongRun support
+ */
+static void __exit longrun_exit(void)
+{
+	cpufreq_unregister_driver(&longrun_driver);
+}
+
+
+MODULE_AUTHOR("Dominik Brodowski <linux@brodo.de>");
+MODULE_DESCRIPTION("LongRun driver for Transmeta Crusoe and "
+		"Efficeon processors.");
+MODULE_LICENSE("GPL");
+
+module_init(longrun_init);
+module_exit(longrun_exit);