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) 1996-2021, 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 #include <setjmp.h>
  28 #include <signal.h>
  29
  30 #include "port/pg_crc32c.h"
  31
  32
  33 static sigjmp_buf illegal_instruction_jump;
  34
  35 /*
  36  * Probe by trying to execute pg_comp_crc32c_armv8().  If the instruction
  37  * isn't available, we expect to get SIGILL, which we can trap.
  38  */
  39 static void
  40 illegal_instruction_handler(SIGNAL_ARGS)
  41 {
  42         siglongjmp(illegal_instruction_jump, 1);
  43 }
  44
  45 static bool
  46 pg_crc32c_armv8_available(void)
  47 {
  48         uint64          data = 42;
  49         int                     result;
  50
  51         /*
  52          * Be careful not to do anything that might throw an error while we have
  53          * the SIGILL handler set to a nonstandard value.
  54          */
  55         pqsignal(SIGILL, illegal_instruction_handler);
  56         if (sigsetjmp(illegal_instruction_jump, 1) == 0)
  57         {
  58                 /* Rather than hard-wiring an expected result, compare to SB8 code */
  59                 result = (pg_comp_crc32c_armv8(0, &data, sizeof(data)) ==
  60                                   pg_comp_crc32c_sb8(0, &data, sizeof(data)));
  61         }
  62         else
  63         {
  64                 /* We got the SIGILL trap */
  65                 result = -1;
  66         }
  67         pqsignal(SIGILL, SIG_DFL);
  68
  69 #ifndef FRONTEND
  70         /* We don't expect this case, so complain loudly */
  71         if (result == 0)
  72                 elog(ERROR, "crc32 hardware and software results disagree");
  73
  74         elog(DEBUG1, "using armv8 crc32 hardware = %d", (result > 0));
  75 #endif
  76
  77         return (result > 0);
  78 }
  79
  80 /*
  81  * This gets called on the first call. It replaces the function pointer
  82  * so that subsequent calls are routed directly to the chosen implementation.
  83  */
  84 static pg_crc32c
  85 pg_comp_crc32c_choose(pg_crc32c crc, const void *data, size_t len)
  86 {
  87         if (pg_crc32c_armv8_available())
  88                 pg_comp_crc32c = pg_comp_crc32c_armv8;
  89         else
  90                 pg_comp_crc32c = pg_comp_crc32c_sb8;
  91
  92         return pg_comp_crc32c(crc, data, len);
  93 }
  94
  95 pg_crc32c       (*pg_comp_crc32c) (pg_crc32c crc, const void *data, size_t len) = pg_comp_crc32c_choose;