src/port/pg_crc32c_armv8_choose.c

   1 /*-------------------------------------------------------------------------
   2  *
   3  * pg_crc32c_armv8_choose.c
   4  *        Choose between ARMv8 and software CRC-32C implementation.
   5  *
   6  * On first call, checks if the CPU we're running on supports the ARMv8
   7  * CRC Extension. If it does, use the special instructions for CRC-32C
   8  * computation. Otherwise, fall back to the pure software implementation
   9  * (slicing-by-8).
  10  *
  11  * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
  12  * Portions Copyright (c) 1994, Regents of the University of California
  13  *
  14  *
  15  * IDENTIFICATION
  16  *        src/port/pg_crc32c_armv8_choose.c
  17  *
  18  *-------------------------------------------------------------------------
  19  */
  20
  21 #ifndef FRONTEND
  22 #include "postgres.h"
  23 #else
  24 #include "postgres_fe.h"
  25 #endif
  26
  27 #if defined(HAVE_ELF_AUX_INFO) || defined(HAVE_GETAUXVAL)
  28 #include <sys/auxv.h>
  29 #if defined(__linux__) && !defined(__aarch64__) && !defined(HWCAP2_CRC32)
  30 #include <asm/hwcap.h>
  31 #endif
  32 #endif
  33
  34 #if defined(__NetBSD__)
  35 #include <sys/sysctl.h>
  36 #if defined(__aarch64__)
  37 #include <aarch64/armreg.h>
  38 #endif
  39 #endif
  40
  41 #include "port/pg_crc32c.h"
  42
  43 static bool
  44 pg_crc32c_armv8_available(void)
  45 {
  46 #if defined(HAVE_ELF_AUX_INFO)
  47         unsigned long value;
  48
  49 #ifdef __aarch64__
  50         return elf_aux_info(AT_HWCAP, &value, sizeof(value)) == 0 &&
  51                 (value & HWCAP_CRC32) != 0;
  52 #else
  53         return elf_aux_info(AT_HWCAP2, &value, sizeof(value)) == 0 &&
  54                 (value & HWCAP2_CRC32) != 0;
  55 #endif
  56 #elif defined(HAVE_GETAUXVAL)
  57 #ifdef __aarch64__
  58         return (getauxval(AT_HWCAP) & HWCAP_CRC32) != 0;
  59 #else
  60         return (getauxval(AT_HWCAP2) & HWCAP2_CRC32) != 0;
  61 #endif
  62 #elif defined(__NetBSD__)
  63         /*
  64          * On NetBSD we can read the Instruction Set Attribute Registers via
  65          * sysctl.  For doubtless-historical reasons the sysctl interface is
  66          * completely different on 64-bit than 32-bit, but the underlying
  67          * registers contain the same fields.
  68          */
  69 #define ISAR0_CRC32_BITPOS 16
  70 #define ISAR0_CRC32_BITWIDTH 4
  71 #define WIDTHMASK(w)    ((1 << (w)) - 1)
  72 #define SYSCTL_CPU_ID_MAXSIZE 64
  73
  74         size_t          len;
  75         uint64          sysctlbuf[SYSCTL_CPU_ID_MAXSIZE];
  76 #if defined(__aarch64__)
  77         /* We assume cpu0 is representative of all the machine's CPUs. */
  78         const char *path = "machdep.cpu0.cpu_id";
  79         size_t          expected_len = sizeof(struct aarch64_sysctl_cpu_id);
  80 #define ISAR0 ((struct aarch64_sysctl_cpu_id *) sysctlbuf)->ac_aa64isar0
  81 #else
  82         const char *path = "machdep.id_isar";
  83         size_t          expected_len = 6 * sizeof(int);
  84 #define ISAR0 ((int *) sysctlbuf)[5]
  85 #endif
  86         uint64          fld;
  87
  88         /* Fetch the appropriate set of register values. */
  89         len = sizeof(sysctlbuf);
  90         memset(sysctlbuf, 0, len);
  91         if (sysctlbyname(path, sysctlbuf, &len, NULL, 0) != 0)
  92                 return false;                   /* perhaps kernel is 64-bit and we aren't? */
  93         if (len != expected_len)
  94                 return false;                   /* kernel API change? */
  95
  96         /* Fetch the CRC32 field from ISAR0. */
  97         fld = (ISAR0 >> ISAR0_CRC32_BITPOS) & WIDTHMASK(ISAR0_CRC32_BITWIDTH);
  98
  99         /*
 100          * Current documentation defines only the field values 0 (No CRC32) and 1
 101          * (CRC32B/CRC32H/CRC32W/CRC32X/CRC32CB/CRC32CH/CRC32CW/CRC32CX).  Assume
 102          * that any future nonzero value will be a superset of 1.
 103          */
 104         return (fld != 0);
 105 #else
 106         return false;
 107 #endif
 108 }
 109
 110 /*
 111  * This gets called on the first call. It replaces the function pointer
 112  * so that subsequent calls are routed directly to the chosen implementation.
 113  */
 114 static pg_crc32c
 115 pg_comp_crc32c_choose(pg_crc32c crc, const void *data, size_t len)
 116 {
 117         if (pg_crc32c_armv8_available())
 118                 pg_comp_crc32c = pg_comp_crc32c_armv8;
 119         else
 120                 pg_comp_crc32c = pg_comp_crc32c_sb8;
 121
 122         return pg_comp_crc32c(crc, data, len);
 123 }
 124
 125 pg_crc32c       (*pg_comp_crc32c) (pg_crc32c crc, const void *data, size_t len) = pg_comp_crc32c_choose;