pg_crc32c_armv8_choose.c

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/*-------------------------------------------------------------------------
 *
 * pg_crc32c_armv8_choose.c
 *    Choose between ARMv8 and software CRC-32C implementation.
 *
 * On first call, checks if the CPU we're running on supports the ARMv8
 * CRC Extension. If it does, use the special instructions for CRC-32C
 * computation. Otherwise, fall back to the pure software implementation
 * (slicing-by-8).
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/port/pg_crc32c_armv8_choose.c
 *
 *-------------------------------------------------------------------------
 */
 
#ifndef FRONTEND
#include "postgres.h"
#else
#include "postgres_fe.h"
#endif
 
#if defined(HAVE_ELF_AUX_INFO) || defined(HAVE_GETAUXVAL)
#include <sys/auxv.h>
#if defined(__linux__) && !defined(__aarch64__) && !defined(HWCAP2_CRC32)
#include <asm/hwcap.h>
#endif
#endif
 
#if defined(__NetBSD__)
#include <sys/sysctl.h>
#if defined(__aarch64__)
#include <aarch64/armreg.h>
#endif
#endif
 
#include "port/pg_crc32c.h"
 
static bool
pg_crc32c_armv8_available(void)
{
#if defined(HAVE_ELF_AUX_INFO)
    unsigned long value;
 
#ifdef __aarch64__
    return elf_aux_info(AT_HWCAP, &value, sizeof(value)) == 0 &&
        (value & HWCAP_CRC32) != 0;
#else
    return elf_aux_info(AT_HWCAP2, &value, sizeof(value)) == 0 &&
        (value & HWCAP2_CRC32) != 0;
#endif
#elif defined(HAVE_GETAUXVAL)
#ifdef __aarch64__
    return (getauxval(AT_HWCAP) & HWCAP_CRC32) != 0;
#else
    return (getauxval(AT_HWCAP2) & HWCAP2_CRC32) != 0;
#endif
#elif defined(__NetBSD__)
    /*
     * On NetBSD we can read the Instruction Set Attribute Registers via
     * sysctl.  For doubtless-historical reasons the sysctl interface is
     * completely different on 64-bit than 32-bit, but the underlying
     * registers contain the same fields.
     */
#define ISAR0_CRC32_BITPOS 16
#define ISAR0_CRC32_BITWIDTH 4
#define WIDTHMASK(w)    ((1 << (w)) - 1)
#define SYSCTL_CPU_ID_MAXSIZE 64
 
    size_t      len;
    uint64      sysctlbuf[SYSCTL_CPU_ID_MAXSIZE];
#if defined(__aarch64__)
    /* We assume cpu0 is representative of all the machine's CPUs. */
    const char *path = "machdep.cpu0.cpu_id";
    size_t      expected_len = sizeof(struct aarch64_sysctl_cpu_id);
#define ISAR0 ((struct aarch64_sysctl_cpu_id *) sysctlbuf)->ac_aa64isar0
#else
    const char *path = "machdep.id_isar";
    size_t      expected_len = 6 * sizeof(int);
#define ISAR0 ((int *) sysctlbuf)[5]
#endif
    uint64      fld;
 
    /* Fetch the appropriate set of register values. */
    len = sizeof(sysctlbuf);
    memset(sysctlbuf, 0, len);
    if (sysctlbyname(path, sysctlbuf, &len, NULL, 0) != 0)
        return false;           /* perhaps kernel is 64-bit and we aren't? */
    if (len != expected_len)
        return false;           /* kernel API change? */
 
    /* Fetch the CRC32 field from ISAR0. */
    fld = (ISAR0 >> ISAR0_CRC32_BITPOS) & WIDTHMASK(ISAR0_CRC32_BITWIDTH);
 
    /*
     * Current documentation defines only the field values 0 (No CRC32) and 1
     * (CRC32B/CRC32H/CRC32W/CRC32X/CRC32CB/CRC32CH/CRC32CW/CRC32CX).  Assume
     * that any future nonzero value will be a superset of 1.
     */
    return (fld != 0);
#else
    return false;
#endif
}
 
/*
 * This gets called on the first call. It replaces the function pointer
 * so that subsequent calls are routed directly to the chosen implementation.
 */
static pg_crc32c
pg_comp_crc32c_choose(pg_crc32c crc, const void *data, size_t len)
{
    if (pg_crc32c_armv8_available())
        pg_comp_crc32c = pg_comp_crc32c_armv8;
    else
        pg_comp_crc32c = pg_comp_crc32c_sb8;
 
    return pg_comp_crc32c(crc, data, len);
}
 
pg_crc32c   (*pg_comp_crc32c) (pg_crc32c crc, const void *data, size_t len) = pg_comp_crc32c_choose;