src/arm/linux/cpuinfo.c

#include <stdbool.h>
#include <stdint.h>
#include <stdlib.h>
#include <stddef.h>
#include <string.h>

#include <linux/api.h>
#include <arm/linux/api.h>
#include <arm/midr.h>
#include <log.h>

/*
 * Size, in chars, of the on-stack buffer used for parsing lines of /proc/cpuinfo.
 * This is also the limit on the length of a single line.
 */
#define BUFFER_SIZE 1024


static uint32_t parse_processor_number(
	const char* processor_start,
	const char* processor_end)
{
	const size_t processor_length = (size_t) (processor_end - processor_start);

	if (processor_length == 0) {
		cpuinfo_log_warning("Processor number in /proc/cpuinfo is ignored: string is empty");
		return 0;
	}

	uint32_t processor_number = 0;
	for (const char* digit_ptr = processor_start; digit_ptr != processor_end; digit_ptr++) {
		const uint32_t digit = (uint32_t) (*digit_ptr - '0');
		if (digit > 10) {
			cpuinfo_log_warning("non-decimal suffix %.*s in /proc/cpuinfo processor number is ignored",
				(int) (processor_end - digit_ptr), digit_ptr);
			break;
		}

		processor_number = processor_number * 10 + digit;
	}

	return processor_number;
}

/*
 *	Full list of ARM features reported in /proc/cpuinfo:
 *	
 *	* swp - support for SWP instruction (deprecated in ARMv7, can be removed in future)
 *	* half - support for half-word loads and stores. These instruction are part of ARMv4,
 *	         so no need to check it on supported CPUs.
 *	* thumb - support for 16-bit Thumb instruction set. Note that BX instruction is detected
 *	          by ARMv4T architecture, not by this flag.
 *	* 26bit - old CPUs merged 26-bit PC and program status register (flags) into 32-bit PC
 *	          and had special instructions for working with packed PC. Now it is all deprecated.
 *	* fastmult - most old ARM CPUs could only compute 2 bits of multiplication result per clock
 *	             cycle, but CPUs with M suffix (e.g. ARM7TDMI) could compute 4 bits per cycle.
 *	             Of course, now it makes no sense.
 *	* fpa - floating point accelerator available. On original ARM ABI all floating-point operations
 *	        generated FPA instructions. If FPA was not available, these instructions generated
 *	        "illegal operation" interrupts, and the OS processed them by emulating the FPA instructions.
 *	        Debian used this ABI before it switched to EABI. Now FPA is deprecated.
 *	* vfp - vector floating point instructions. Available on most modern CPUs (as part of VFPv3).
 *	        Required by Android ARMv7A ABI and by Ubuntu on ARM.
 *              Note: there is no flag for VFPv2.
 *	* edsp - V5E instructions: saturating add/sub and 16-bit x 16-bit -> 32/64-bit multiplications.
 *	         Required on Android, supported by all CPUs in production.
 *	* java - Jazelle extension. Supported on most CPUs.
 *	* iwmmxt - Intel/Marvell Wireless MMX instructions. 64-bit integer SIMD.
 *	           Supported on XScale (Since PXA270) and Sheeva (PJ1, PJ4) architectures.
 *	           Note that there is no flag for WMMX2 instructions.
 *	* crunch - Maverick Crunch instructions. Junk.
 *	* thumbee - ThumbEE instructions. Almost no documentation is available.
 *	* neon - NEON instructions (aka Advanced SIMD). MVFR1 register gives more
 *	         fine-grained information on particular supported features, but
 *	         the Linux kernel exports only a single flag for all of them.
 *	         According to ARMv7A docs it also implies the availability of VFPv3
 *	         (with 32 double-precision registers d0-d31).
 *	* vfpv3 - VFPv3 instructions. Available on most modern CPUs. Augment VFPv2 by
 *	          conversion to/from integers and load constant instructions.
 *	          Required by Android ARMv7A ABI and by Ubuntu on ARM.
 *	* vfpv3d16 - VFPv3 instructions with only 16 double-precision registers (d0-d15).
 *	* tls - software thread ID registers.
 *	        Used by kernel (and likely libc) for efficient implementation of TLS.
 *	* vfpv4 - fused multiply-add instructions.
 *	* idiva - DIV instructions available in ARM mode.
 *	* idivt - DIV instructions available in Thumb mode.
 *  * vfpd32 - VFP (of any version) with 32 double-precision registers d0-d31.
 *  * lpae - Large Physical Address Extension (physical address up to 40 bits).
 *  * evtstrm - generation of Event Stream by timer.
 *  * aes - AES instructions.
 *  * pmull - Polinomial Multiplication instructions.
 *  * sha1 - SHA1 instructions.
 *  * sha2 - SHA2 instructions.
 *  * crc32 - CRC32 instructions.
 *
 *	/proc/cpuinfo on ARM is populated in file arch/arm/kernel/setup.c in Linux kernel
 *	Note that some devices may use patched Linux kernels with different feature names.
 *	However, the names above were checked on a large number of /proc/cpuinfo listings.
 */
static void parse_features(
	const char* features_start,
	const char* features_end,
	struct cpuinfo_arm_linux_processor processor[restrict static 1])
{
	const char* feature_start = features_start;
	const char* feature_end;

	/* Mark the features as valid */
	processor->flags |= CPUINFO_ARM_LINUX_VALID_FEATURES | CPUINFO_ARM_LINUX_VALID_PROCESSOR;

	do {
		feature_end = feature_start + 1;
		for (; feature_end != features_end; feature_end++) {
			if (*feature_end == ' ') {
				break;
			}
		}
		const size_t feature_length = (size_t) (feature_end - feature_start);

		switch (feature_length) {
			case 2:
				if (memcmp(feature_start, "fp", feature_length) == 0) {
#if CPUINFO_ARCH_ARM64
					processor->features |= CPUINFO_ARM_LINUX_FEATURE_FP;
#endif
#if CPUINFO_ARCH_ARM
				} else if (memcmp(feature_start, "wp", feature_length) == 0) {
					/*
					 * Some AArch64 kernels, including the one on Nexus 5X,
					 * erroneously report "swp" as "wp" to AArch32 programs
					 */
					processor->features |= CPUINFO_ARM_LINUX_FEATURE_SWP;
#endif
				} else {
					goto unexpected;
				}
				break;
			case 3:
				if (memcmp(feature_start, "aes", feature_length) == 0) {
					#if CPUINFO_ARCH_ARM
						processor->features2 |= CPUINFO_ARM_LINUX_FEATURE2_AES;
					#elif CPUINFO_ARCH_ARM64
						processor->features |= CPUINFO_ARM_LINUX_FEATURE_AES;
					#endif
#if CPUINFO_ARCH_ARM
				} else if (memcmp(feature_start, "swp", feature_length) == 0) {
					processor->features |= CPUINFO_ARM_LINUX_FEATURE_SWP;
				} else if (memcmp(feature_start, "fpa", feature_length) == 0) {
					processor->features |= CPUINFO_ARM_LINUX_FEATURE_FPA;
				} else if (memcmp(feature_start, "vfp", feature_length) == 0) {
					processor->features |= CPUINFO_ARM_LINUX_FEATURE_VFP;
				} else if (memcmp(feature_start, "tls", feature_length) == 0) {
					processor->features |= CPUINFO_ARM_LINUX_FEATURE_TLS;
#endif /* CPUINFO_ARCH_ARM */
				} else {
					goto unexpected;
				}
				break;
			case 4:
				if (memcmp(feature_start, "sha1", feature_length) == 0) {
					#if CPUINFO_ARCH_ARM
						processor->features2 |= CPUINFO_ARM_LINUX_FEATURE2_SHA1;
					#elif CPUINFO_ARCH_ARM64
						processor->features |= CPUINFO_ARM_LINUX_FEATURE_SHA1;
					#endif
				} else if (memcmp(feature_start, "sha2", feature_length) == 0) {
					#if CPUINFO_ARCH_ARM
						processor->features2 |= CPUINFO_ARM_LINUX_FEATURE2_SHA2;
					#elif CPUINFO_ARCH_ARM64
						processor->features |= CPUINFO_ARM_LINUX_FEATURE_SHA2;
					#endif
				} else if (memcmp(feature_start, "fphp", feature_length) == 0) {
					#if CPUINFO_ARCH_ARM64
						processor->features |= CPUINFO_ARM_LINUX_FEATURE_FPHP;
					#endif
				} else if (memcmp(feature_start, "fcma", feature_length) == 0) {
					#if CPUINFO_ARCH_ARM64
						processor->features |= CPUINFO_ARM_LINUX_FEATURE_FCMA;
					#endif
#if CPUINFO_ARCH_ARM
				} else if (memcmp(feature_start, "half", feature_length) == 0) {
					processor->features |= CPUINFO_ARM_LINUX_FEATURE_HALF;
				} else if (memcmp(feature_start, "edsp", feature_length) == 0) {
					processor->features |= CPUINFO_ARM_LINUX_FEATURE_EDSP;
				} else if (memcmp(feature_start, "java", feature_length) == 0) {
					processor->features |= CPUINFO_ARM_LINUX_FEATURE_JAVA;
				} else if (memcmp(feature_start, "neon", feature_length) == 0) {
					processor->features |= CPUINFO_ARM_LINUX_FEATURE_NEON;
				} else if (memcmp(feature_start, "lpae", feature_length) == 0) {
					processor->features |= CPUINFO_ARM_LINUX_FEATURE_LPAE;
				} else if (memcmp(feature_start, "tlsi", feature_length) == 0) {
					/*
					 * Some AArch64 kernels, including the one on Nexus 5X,
					 * erroneously report "tls" as "tlsi" to AArch32 programs
					 */
					processor->features |= CPUINFO_ARM_LINUX_FEATURE_TLS;
#endif /* CPUINFO_ARCH_ARM */
				} else {
					goto unexpected;
				}
				break;
			case 5:
				if (memcmp(feature_start, "pmull", feature_length) == 0) {
					#if CPUINFO_ARCH_ARM
						processor->features2 |= CPUINFO_ARM_LINUX_FEATURE2_PMULL;
					#elif CPUINFO_ARCH_ARM64
						processor->features |= CPUINFO_ARM_LINUX_FEATURE_PMULL;
					#endif
				} else if (memcmp(feature_start, "crc32", feature_length) == 0) {
					#if CPUINFO_ARCH_ARM
						processor->features2 |= CPUINFO_ARM_LINUX_FEATURE2_CRC32;
					#elif CPUINFO_ARCH_ARM64
						processor->features |= CPUINFO_ARM_LINUX_FEATURE_CRC32;
					#endif
				} else if (memcmp(feature_start, "asimd", feature_length) == 0) {
					#if CPUINFO_ARCH_ARM64
						processor->features |= CPUINFO_ARM_LINUX_FEATURE_ASIMD;
					#endif
				} else if (memcmp(feature_start, "cpuid", feature_length) == 0) {
					#if CPUINFO_ARCH_ARM64
						processor->features |= CPUINFO_ARM_LINUX_FEATURE_CPUID;
					#endif
				} else if (memcmp(feature_start, "jscvt", feature_length) == 0) {
					#if CPUINFO_ARCH_ARM64
						processor->features |= CPUINFO_ARM_LINUX_FEATURE_JSCVT;
					#endif
				} else if (memcmp(feature_start, "lrcpc", feature_length) == 0) {
					#if CPUINFO_ARCH_ARM64
						processor->features |= CPUINFO_ARM_LINUX_FEATURE_LRCPC;
					#endif
#if CPUINFO_ARCH_ARM
				} else if (memcmp(feature_start, "thumb", feature_length) == 0) {
					processor->features |= CPUINFO_ARM_LINUX_FEATURE_THUMB;
				} else if (memcmp(feature_start, "26bit", feature_length) == 0) {
					processor->features |= CPUINFO_ARM_LINUX_FEATURE_26BIT;
				} else if (memcmp(feature_start, "vfpv3", feature_length) == 0) {
					processor->features |= CPUINFO_ARM_LINUX_FEATURE_VFPV3;
				} else if (memcmp(feature_start, "vfpv4", feature_length) == 0) {
					processor->features |= CPUINFO_ARM_LINUX_FEATURE_VFPV4;
				} else if (memcmp(feature_start, "idiva", feature_length) == 0) {
					processor->features |= CPUINFO_ARM_LINUX_FEATURE_IDIVA;
				} else if (memcmp(feature_start, "idivt", feature_length) == 0) {
					processor->features |= CPUINFO_ARM_LINUX_FEATURE_IDIVT;
#endif /* CPUINFO_ARCH_ARM */
				} else {
					goto unexpected;
				}
 				break;
#if CPUINFO_ARCH_ARM
			case 6:
				if (memcmp(feature_start, "iwmmxt", feature_length) == 0) {
					processor->features |= CPUINFO_ARM_LINUX_FEATURE_IWMMXT;
				} else if (memcmp(feature_start, "crunch", feature_length) == 0) {
					processor->features |= CPUINFO_ARM_LINUX_FEATURE_CRUNCH;
				} else if (memcmp(feature_start, "vfpd32", feature_length) == 0) {
					processor->features |= CPUINFO_ARM_LINUX_FEATURE_VFPD32;
				} else {
					goto unexpected;
				}
				break;
#endif /* CPUINFO_ARCH_ARM */
			case 7:
				if (memcmp(feature_start, "evtstrm", feature_length) == 0) {
					processor->features |= CPUINFO_ARM_LINUX_FEATURE_EVTSTRM;
				} else if (memcmp(feature_start, "atomics", feature_length) == 0) {
					#if CPUINFO_ARCH_ARM64
						processor->features |= CPUINFO_ARM_LINUX_FEATURE_ATOMICS;
					#endif
				} else if (memcmp(feature_start, "asimdhp", feature_length) == 0) {
					#if CPUINFO_ARCH_ARM64
						processor->features |= CPUINFO_ARM_LINUX_FEATURE_ASIMDHP;
					#endif
#if CPUINFO_ARCH_ARM
				} else if (memcmp(feature_start, "thumbee", feature_length) == 0) {
					processor->features |= CPUINFO_ARM_LINUX_FEATURE_THUMBEE;
#endif /* CPUINFO_ARCH_ARM */
				} else {
					goto unexpected;
				}
				break;
			case 8:
				if (memcmp(feature_start, "asimdrdm", feature_length) == 0) {
					#if CPUINFO_ARCH_ARM64
						processor->features |= CPUINFO_ARM_LINUX_FEATURE_ASIMDRDM;
					#endif
#if CPUINFO_ARCH_ARM
				} else if (memcmp(feature_start, "fastmult", feature_length) == 0) {
					processor->features |= CPUINFO_ARM_LINUX_FEATURE_FASTMULT;
				} else if (memcmp(feature_start, "vfpv3d16", feature_length) == 0) {
					processor->features |= CPUINFO_ARM_LINUX_FEATURE_VFPV3D16;
#endif /* CPUINFO_ARCH_ARM */
				} else {
					goto unexpected;
				}
				break;
			default:
			unexpected:
				cpuinfo_log_warning("unexpected /proc/cpuinfo feature \"%.*s\" is ignored",
					(int) feature_length, feature_start);
				break;
		}
		feature_start = feature_end;
		for (; feature_start != features_end; feature_start++) {
			if (*feature_start != ' ') {
				break;
			}
		}
	} while (feature_start != feature_end);
}

static void parse_cpu_architecture(
	const char* cpu_architecture_start,
	const char* cpu_architecture_end,
	struct cpuinfo_arm_linux_processor processor[restrict static 1])
{
	const size_t cpu_architecture_length = (size_t) (cpu_architecture_end - cpu_architecture_start);
	/* Early AArch64 kernels report "CPU architecture: AArch64" instead of a numeric value 8 */
	if (cpu_architecture_length == 7) {
		if (memcmp(cpu_architecture_start, "AArch64", cpu_architecture_length) == 0) {
			processor->midr = midr_set_architecture(processor->midr, UINT32_C(0xF));
			processor->architecture_version = 8;
			processor->flags |= CPUINFO_ARM_LINUX_VALID_ARCHITECTURE | CPUINFO_ARM_LINUX_VALID_PROCESSOR;
			return;
		}
	}


	uint32_t architecture = 0;
	const char* cpu_architecture_ptr = cpu_architecture_start;
	for (; cpu_architecture_ptr != cpu_architecture_end; cpu_architecture_ptr++) {
		const uint32_t digit = (*cpu_architecture_ptr) - '0';

		/* Verify that CPU architecture is a decimal number */
		if (digit >= 10) {
			break;
		}

		architecture = architecture * 10 + digit;
	}

	if (cpu_architecture_ptr == cpu_architecture_start) {
		cpuinfo_log_warning("CPU architecture %.*s in /proc/cpuinfo is ignored due to non-digit at the beginning of the string",
			(int) cpu_architecture_length, cpu_architecture_start);
	} else {
		if (architecture != 0) {
			processor->architecture_version = architecture;
			processor->flags |= CPUINFO_ARM_LINUX_VALID_ARCHITECTURE | CPUINFO_ARM_LINUX_VALID_PROCESSOR;

			for (; cpu_architecture_ptr != cpu_architecture_end; cpu_architecture_ptr++) {
				const char feature = *cpu_architecture_ptr;
				switch (feature) {
#if CPUINFO_ARCH_ARM
					case 'T':
						processor->architecture_flags |= CPUINFO_ARM_LINUX_ARCH_T;
						break;
					case 'E':
						processor->architecture_flags |= CPUINFO_ARM_LINUX_ARCH_E;
						break;
					case 'J':
						processor->architecture_flags |= CPUINFO_ARM_LINUX_ARCH_J;
						break;
#endif /* CPUINFO_ARCH_ARM */
					case ' ':
					case '\t':
						/* Ignore whitespace at the end */
						break;
					default:
						cpuinfo_log_warning("skipped unknown architectural feature '%c' for ARMv%"PRIu32,
							feature, architecture);
						break;
				}
			}
		} else {
			cpuinfo_log_warning("CPU architecture %.*s in /proc/cpuinfo is ignored due to invalid value (0)",
				(int) cpu_architecture_length, cpu_architecture_start);
		}
	}

	uint32_t midr_architecture = UINT32_C(0xF);
#if CPUINFO_ARCH_ARM
	switch (processor->architecture_version) {
		case 6:
			midr_architecture = UINT32_C(0x7); /* ARMv6 */
			break;
		case 5:
			if ((processor->architecture_flags & CPUINFO_ARM_LINUX_ARCH_TEJ) == CPUINFO_ARM_LINUX_ARCH_TEJ) {
				midr_architecture = UINT32_C(0x6); /* ARMv5TEJ */
			} else if ((processor->architecture_flags & CPUINFO_ARM_LINUX_ARCH_TE) == CPUINFO_ARM_LINUX_ARCH_TE) {
				midr_architecture = UINT32_C(0x5); /* ARMv5TE */
			} else {
				midr_architecture = UINT32_C(0x4); /* ARMv5T */
			}
			break;
	}
#endif
	processor->midr = midr_set_architecture(processor->midr, midr_architecture);
}

static void parse_cpu_part(
	const char* cpu_part_start,
	const char* cpu_part_end,
	struct cpuinfo_arm_linux_processor processor[restrict static 1])
{
	const size_t cpu_part_length = (size_t) (cpu_part_end - cpu_part_start);

	/*
	 * CPU part should contain hex prefix (0x) and one to three hex digits.
	 * I have never seen less than three digits as a value of this field,
	 * but I don't think it is impossible to see such values in future.
	 * Value can not contain more than three hex digits since
	 * Main ID Register (MIDR) assigns only a 12-bit value for CPU part.
	 */
	if (cpu_part_length < 3 || cpu_part_length > 5) {
		cpuinfo_log_warning("CPU part %.*s in /proc/cpuinfo is ignored due to unexpected length (%zu)",
			(int) cpu_part_length, cpu_part_start, cpu_part_length);
		return;
	}

	/* Verify the presence of hex prefix */
	if (cpu_part_start[0] != '0' || cpu_part_start[1] != 'x') {
		cpuinfo_log_warning("CPU part %.*s in /proc/cpuinfo is ignored due to lack of 0x prefix",
			(int) cpu_part_length, cpu_part_start);
		return;
	}

	/* Verify that characters after hex prefix are hexadecimal digits and decode them */
	uint32_t cpu_part = 0;
	for (const char* digit_ptr = cpu_part_start + 2; digit_ptr != cpu_part_end; digit_ptr++) {
		const char digit_char = *digit_ptr;
		uint32_t digit;
		if (digit_char >= '0' && digit_char <= '9') {
			digit = digit_char - '0';
		} else if ((uint32_t) (digit_char - 'A') < 6) {
			digit = 10 + (digit_char - 'A');
		} else if ((uint32_t) (digit_char - 'a') < 6) {
			digit = 10 + (digit_char - 'a');
		} else {
			cpuinfo_log_warning("CPU part %.*s in /proc/cpuinfo is ignored due to unexpected non-hex character %c at offset %zu",
				(int) cpu_part_length, cpu_part_start, digit_char, (size_t) (digit_ptr - cpu_part_start));
			return;
		}
		cpu_part = cpu_part * 16 + digit;
	}

	processor->midr = midr_set_part(processor->midr, cpu_part);
	processor->flags |= CPUINFO_ARM_LINUX_VALID_PART | CPUINFO_ARM_LINUX_VALID_PROCESSOR;
}

static void parse_cpu_implementer(
	const char* cpu_implementer_start,
	const char* cpu_implementer_end,
	struct cpuinfo_arm_linux_processor processor[restrict static 1])
{
	const size_t cpu_implementer_length = cpu_implementer_end - cpu_implementer_start;

	/*
	 * Value should contain hex prefix (0x) and one or two hex digits.
	 * I have never seen single hex digit as a value of this field,
	 * but I don't think it is impossible in future.
	 * Value can not contain more than two hex digits since
	 * Main ID Register (MIDR) assigns only an 8-bit value for CPU implementer.
	 */
	switch (cpu_implementer_length) {
		case 3:
		case 4:
			break;
		default:
		cpuinfo_log_warning("CPU implementer %.*s in /proc/cpuinfo is ignored due to unexpected length (%zu)",
			(int) cpu_implementer_length, cpu_implementer_start, cpu_implementer_length);
		return;
	}

	/* Verify the presence of hex prefix */
	if (cpu_implementer_start[0] != '0' || cpu_implementer_start[1] != 'x') {
		cpuinfo_log_warning("CPU implementer %.*s in /proc/cpuinfo is ignored due to lack of 0x prefix",
			(int) cpu_implementer_length, cpu_implementer_start);
		return;
	}

	/* Verify that characters after hex prefix are hexadecimal digits and decode them */
	uint32_t cpu_implementer = 0;
	for (const char* digit_ptr = cpu_implementer_start + 2; digit_ptr != cpu_implementer_end; digit_ptr++) {
		const char digit_char = *digit_ptr;
		uint32_t digit;
		if (digit_char >= '0' && digit_char <= '9') {
			digit = digit_char - '0';
		} else if ((uint32_t) (digit_char - 'A') < 6) {
			digit = 10 + (digit_char - 'A');
		} else if ((uint32_t) (digit_char - 'a') < 6) {
			digit = 10 + (digit_char - 'a');
		} else {
			cpuinfo_log_warning("CPU implementer %.*s in /proc/cpuinfo is ignored due to unexpected non-hex character '%c' at offset %zu",
				(int) cpu_implementer_length, cpu_implementer_start, digit_char, (size_t) (digit_ptr - cpu_implementer_start));
			return;
		}
		cpu_implementer = cpu_implementer * 16 + digit;
	}

	processor->midr = midr_set_implementer(processor->midr, cpu_implementer);
	processor->flags |= CPUINFO_ARM_LINUX_VALID_IMPLEMENTER | CPUINFO_ARM_LINUX_VALID_PROCESSOR;
}

static void parse_cpu_variant(
	const char* cpu_variant_start,
	const char* cpu_variant_end,
	struct cpuinfo_arm_linux_processor processor[restrict static 1])
{
	const size_t cpu_variant_length = cpu_variant_end - cpu_variant_start;

	/*
	 * Value should contain hex prefix (0x) and one hex digit.
	 * Value can not contain more than one hex digits since
	 * Main ID Register (MIDR) assigns only a 4-bit value for CPU variant.
	 */
	if (cpu_variant_length != 3) {
		cpuinfo_log_warning("CPU variant %.*s in /proc/cpuinfo is ignored due to unexpected length (%zu)",
			(int) cpu_variant_length, cpu_variant_start, cpu_variant_length);
		return;
	}

	/* Skip if there is no hex prefix (0x) */
	if (cpu_variant_start[0] != '0' || cpu_variant_start[1] != 'x') {
		cpuinfo_log_warning("CPU variant %.*s in /proc/cpuinfo is ignored due to lack of 0x prefix",
			(int) cpu_variant_length, cpu_variant_start);
		return;
	}

	/* Check if the value after hex prefix is indeed a hex digit and decode it. */
	const char digit_char = cpu_variant_start[2];
	uint32_t cpu_variant;
	if ((uint32_t) (digit_char - '0') < 10) {
		cpu_variant = (uint32_t) (digit_char - '0');
	} else if ((uint32_t) (digit_char - 'A') < 6) {
		cpu_variant = 10 + (uint32_t) (digit_char - 'A');
	} else if ((uint32_t) (digit_char - 'a') < 6) {
		cpu_variant = 10 + (uint32_t) (digit_char - 'a');
	} else {
		cpuinfo_log_warning("CPU variant %.*s in /proc/cpuinfo is ignored due to unexpected non-hex character '%c'",
			(int) cpu_variant_length, cpu_variant_start, digit_char);
		return;
	}

	processor->midr = midr_set_variant(processor->midr, cpu_variant);
	processor->flags |= CPUINFO_ARM_LINUX_VALID_VARIANT | CPUINFO_ARM_LINUX_VALID_PROCESSOR;
}

static void parse_cpu_revision(
	const char* cpu_revision_start,
	const char* cpu_revision_end,
	struct cpuinfo_arm_linux_processor processor[restrict static 1])
{
	uint32_t cpu_revision = 0;
	for (const char* digit_ptr = cpu_revision_start; digit_ptr != cpu_revision_end; digit_ptr++) {
		const uint32_t digit = (uint32_t) (*digit_ptr - '0');

		/* Verify that the character in CPU revision is a decimal digit */
		if (digit >= 10) {
			cpuinfo_log_warning("CPU revision %.*s in /proc/cpuinfo is ignored due to unexpected non-digit character '%c' at offset %zu",
				(int) (cpu_revision_end - cpu_revision_start), cpu_revision_start,
				*digit_ptr, (size_t) (digit_ptr - cpu_revision_start));
			return;
		}

		cpu_revision = cpu_revision * 10 + digit;
	}

	processor->midr = midr_set_revision(processor->midr, cpu_revision);
	processor->flags |= CPUINFO_ARM_LINUX_VALID_REVISION | CPUINFO_ARM_LINUX_VALID_PROCESSOR;
}

#if CPUINFO_ARCH_ARM
/*
 * Decode one of the cache-related numbers reported by Linux kernel
 * for pre-ARMv7 architecture.
 * An example cache-related information in /proc/cpuinfo:
 *
 *      I size          : 32768
 *      I assoc         : 4
 *      I line length   : 32
 *      I sets          : 256
 *      D size          : 16384
 *      D assoc         : 4
 *      D line length   : 32
 *      D sets          : 128
 *
 */
static void parse_cache_number(
	const char* number_start,
	const char* number_end,
	const char* number_name,
	uint32_t number_ptr[restrict static 1],
	uint32_t flags[restrict static 1],
	uint32_t number_mask)
{
	uint32_t number = 0;
	for (const char* digit_ptr = number_start; digit_ptr != number_end; digit_ptr++) {
		const uint32_t digit = *digit_ptr - '0';
		if (digit >= 10) {
			cpuinfo_log_warning("%s %.*s in /proc/cpuinfo is ignored due to unexpected non-digit character '%c' at offset %zu",
				number_name, (int) (number_end - number_start), number_start,
				*digit_ptr, (size_t) (digit_ptr - number_start));
			return;
		}

		number = number * 10 + digit;
	}

	if (number == 0) {
		cpuinfo_log_warning("%s %.*s in /proc/cpuinfo is ignored due to invalid value of zero reported by the kernel",
			number_name, (int) (number_end - number_start), number_start);
	}

	/* If the number specifies a cache line size, verify that is a reasonable power of 2 */
	if (number_mask & CPUINFO_ARM_LINUX_VALID_CACHE_LINE) {
		switch (number) {
			case 16:
			case 32:
			case 64:
			case 128:
				break;
			default:
				cpuinfo_log_warning("invalid %s %.*s is ignored: a value of 16, 32, 64, or 128 expected",
					number_name, (int) (number_end - number_start), number_start);			
		}
	}

	*number_ptr = number;
	*flags |= number_mask | CPUINFO_ARM_LINUX_VALID_PROCESSOR;
}
#endif /* CPUINFO_ARCH_ARM */

struct proc_cpuinfo_parser_state {
	char* hardware;
	uint32_t processor_index;
	uint32_t max_processors_count;
	struct cpuinfo_arm_linux_processor* processors;
	struct cpuinfo_arm_linux_processor dummy_processor;
};

/*
 *	Decode a single line of /proc/cpuinfo information.
 *	Lines have format <words-with-spaces>[ ]*:[ ]<space-separated words>
 *	An example of /proc/cpuinfo (from Pandaboard-ES):
 *
 *		Processor       : ARMv7 Processor rev 10 (v7l)
 *		processor       : 0
 *		BogoMIPS        : 1392.74
 *
 *		processor       : 1
 *		BogoMIPS        : 1363.33
 *
 *		Features        : swp half thumb fastmult vfp edsp thumbee neon vfpv3
 *		CPU implementer : 0x41
 *		CPU architecture: 7
 *		CPU variant     : 0x2
 *		CPU part        : 0xc09
 *		CPU revision    : 10
 *
 *		Hardware        : OMAP4 Panda board
 *		Revision        : 0020
 *		Serial          : 0000000000000000
 */
static bool parse_line(
	const char* line_start,
	const char* line_end,
	struct proc_cpuinfo_parser_state state[restrict static 1],
	uint64_t line_number)
{
	/* Empty line. Skip. */
	if (line_start == line_end) {
		return true;
	}
	
	/* Search for ':' on the line. */
	const char* separator = line_start;
	for (; separator != line_end; separator++) {
		if (*separator == ':') {
			break;
		}
	}
	/* Skip line if no ':' separator was found. */
	if (separator == line_end) {
		cpuinfo_log_warning("Line %.*s in /proc/cpuinfo is ignored: key/value separator ':' not found",
			(int) (line_end - line_start), line_start);
		return true;
	}

	/* Skip trailing spaces in key part. */
	const char* key_end = separator;
	for (; key_end != line_start; key_end--) {
		if (key_end[-1] != ' ' && key_end[-1] != '\t') {
			break;
		}
	}
	/* Skip line if key contains nothing but spaces. */
	if (key_end == line_start) {
		cpuinfo_log_warning("Line %.*s in /proc/cpuinfo is ignored: key contains only spaces",
			(int) (line_end - line_start), line_start);
		return true;
	}

	/* Skip leading spaces in value part. */
	const char* value_start = separator + 1;
	for (; value_start != line_end; value_start++) {
		if (*value_start != ' ') {
			break;
		}
	}
	/* Value part contains nothing but spaces. Skip line. */
	if (value_start == line_end) {
		cpuinfo_log_warning("Line %.*s in /proc/cpuinfo is ignored: value contains only spaces",
			(int) (line_end - line_start), line_start);
		return true;
	}

	/* Skip trailing spaces in value part (if any) */
	const char* value_end = line_end;
	for (; value_end != value_start; value_end--) {
		if (value_end[-1] != ' ') {
			break;
		}
	}

	const uint32_t processor_index      = state->processor_index;
	const uint32_t max_processors_count = state->max_processors_count;
	struct cpuinfo_arm_linux_processor* processors = state->processors;
	struct cpuinfo_arm_linux_processor* processor  = &state->dummy_processor;
	if (processor_index < max_processors_count) {
		processor = &processors[processor_index];
	}

	const size_t key_length = key_end - line_start;
	switch (key_length) {
		case 6:
			if (memcmp(line_start, "Serial", key_length) == 0) {
				/* Usually contains just zeros, useless */
#if CPUINFO_ARCH_ARM
			} else if (memcmp(line_start, "I size", key_length) == 0) {
				parse_cache_number(value_start, value_end,
					"instruction cache size", &processor->proc_cpuinfo_cache.i_size,
					&processor->flags, CPUINFO_ARM_LINUX_VALID_ICACHE_SIZE);
			} else if (memcmp(line_start, "I sets", key_length) == 0) {
				parse_cache_number(value_start, value_end,
					"instruction cache sets", &processor->proc_cpuinfo_cache.i_sets,
					&processor->flags, CPUINFO_ARM_LINUX_VALID_ICACHE_SETS);
			} else if (memcmp(line_start, "D size", key_length) == 0) {
				parse_cache_number(value_start, value_end,
					"data cache size", &processor->proc_cpuinfo_cache.d_size,
					&processor->flags, CPUINFO_ARM_LINUX_VALID_DCACHE_SIZE);
			} else if (memcmp(line_start, "D sets", key_length) == 0) {
				parse_cache_number(value_start, value_end,
					"data cache sets", &processor->proc_cpuinfo_cache.d_sets,
					&processor->flags, CPUINFO_ARM_LINUX_VALID_DCACHE_SETS);
#endif /* CPUINFO_ARCH_ARM */
			} else {
				goto unknown;
			}
			break;
#if CPUINFO_ARCH_ARM
		case 7:
			if (memcmp(line_start, "I assoc", key_length) == 0) {
				parse_cache_number(value_start, value_end,
					"instruction cache associativity", &processor->proc_cpuinfo_cache.i_assoc,
					&processor->flags, CPUINFO_ARM_LINUX_VALID_ICACHE_WAYS);
			} else if (memcmp(line_start, "D assoc", key_length) == 0) {
				parse_cache_number(value_start, value_end,
					"data cache associativity", &processor->proc_cpuinfo_cache.d_assoc,
					&processor->flags, CPUINFO_ARM_LINUX_VALID_DCACHE_WAYS);
			} else {
				goto unknown;
			}
			break;
#endif /* CPUINFO_ARCH_ARM */
		case 8:
			if (memcmp(line_start, "CPU part", key_length) == 0) {
				parse_cpu_part(value_start, value_end, processor);
			} else if (memcmp(line_start, "Features", key_length) == 0) {
				parse_features(value_start, value_end, processor);
			} else if (memcmp(line_start, "BogoMIPS", key_length) == 0) {
				/* BogoMIPS is useless, don't parse */
			} else if (memcmp(line_start, "Hardware", key_length) == 0) {
				size_t value_length = value_end - value_start;
				if (value_length > CPUINFO_HARDWARE_VALUE_MAX) {
					cpuinfo_log_info(
						"length of Hardware value \"%.*s\" in /proc/cpuinfo exceeds limit (%d): truncating to the limit",
						(int) value_length, value_start, CPUINFO_HARDWARE_VALUE_MAX);
					value_length = CPUINFO_HARDWARE_VALUE_MAX;
				} else {
					state->hardware[value_length] = '\0';
				}
				memcpy(state->hardware, value_start, value_length);
				cpuinfo_log_debug("parsed /proc/cpuinfo Hardware = \"%.*s\"", (int) value_length, value_start);
			} else if (memcmp(line_start, "Revision", key_length) == 0) {
				/* Board revision, no use for now */
			} else {
				goto unknown;
			}
			break;
		case 9:
			if (memcmp(line_start, "processor", key_length) == 0) {
				const uint32_t new_processor_index = parse_processor_number(value_start, value_end);
				if (new_processor_index < processor_index) {
					/* Strange: decreasing processor number */
					cpuinfo_log_warning(
						"unexpectedly low processor number %"PRIu32" following processor %"PRIu32" in /proc/cpuinfo",
						new_processor_index, processor_index);
				} else if (new_processor_index > processor_index + 1) {
					/* Strange, but common: skipped processor $(processor_index + 1) */
					cpuinfo_log_info(
						"unexpectedly high processor number %"PRIu32" following processor %"PRIu32" in /proc/cpuinfo",
						new_processor_index, processor_index);
				}
				if (new_processor_index < max_processors_count) {
					/* Record that the processor was mentioned in /proc/cpuinfo */
					processors[new_processor_index].flags |= CPUINFO_ARM_LINUX_VALID_PROCESSOR;
				} else {
					/* Log and ignore processor */
					cpuinfo_log_warning("processor %"PRIu32" in /proc/cpuinfo is ignored: index exceeds system limit %"PRIu32,
						new_processor_index, max_processors_count - 1);
				}
				state->processor_index = new_processor_index;
				return true;
			} else if (memcmp(line_start, "Processor", key_length) == 0) {
				/* TODO: parse to fix misreported architecture, similar to Android's cpufeatures */
			} else {
				goto unknown;
			}
			break;
		case 11:
			if (memcmp(line_start, "CPU variant", key_length) == 0) {
				parse_cpu_variant(value_start, value_end, processor);
			} else {
				goto unknown;
			}
			break;
		case 12:
			if (memcmp(line_start, "CPU revision", key_length) == 0) {
				parse_cpu_revision(value_start, value_end, processor);
			} else {
				goto unknown;
			}
			break;
#if CPUINFO_ARCH_ARM
		case 13:
			if (memcmp(line_start, "I line length", key_length) == 0) {
				parse_cache_number(value_start, value_end,
					"instruction cache line size", &processor->proc_cpuinfo_cache.i_line_length,
					&processor->flags, CPUINFO_ARM_LINUX_VALID_ICACHE_LINE);
			} else if (memcmp(line_start, "D line length", key_length) == 0) {
				parse_cache_number(value_start, value_end,
					"data cache line size", &processor->proc_cpuinfo_cache.d_line_length,
					&processor->flags, CPUINFO_ARM_LINUX_VALID_DCACHE_LINE);
			} else {
				goto unknown;
			}
			break;
#endif /* CPUINFO_ARCH_ARM */
		case 15:
			if (memcmp(line_start, "CPU implementer", key_length) == 0) {
				parse_cpu_implementer(value_start, value_end, processor);
			} else if (memcmp(line_start, "CPU implementor", key_length) == 0) {
				parse_cpu_implementer(value_start, value_end, processor);
			} else {
				goto unknown;
			}
			break;
		case 16:
			if (memcmp(line_start, "CPU architecture", key_length) == 0) {
				parse_cpu_architecture(value_start, value_end, processor);
			} else {
				goto unknown;
			}
			break;
		default:
		unknown:
			cpuinfo_log_debug("unknown /proc/cpuinfo key: %.*s", (int) key_length, line_start);

	}
	return true;
}

bool cpuinfo_arm_linux_parse_proc_cpuinfo(
	char hardware[restrict static CPUINFO_HARDWARE_VALUE_MAX],
	uint32_t max_processors_count,
	struct cpuinfo_arm_linux_processor processors[restrict static max_processors_count])
{
	struct proc_cpuinfo_parser_state state = {
		.hardware = hardware,
		.processor_index = 0,
		.max_processors_count = max_processors_count,
		.processors = processors,
	};
	return cpuinfo_linux_parse_multiline_file("/proc/cpuinfo", BUFFER_SIZE,
		(cpuinfo_line_callback) parse_line, &state);
}