Further improve code for probing the availability of ARM CRC instructions.

Andrew Gierth pointed out that commit 1c72ec6f4 would yield the wrong
answer on big-endian ARM systems, because the data being CRC'd would be
different.  To fix that, and avoid the rather unsightly hard-wired
constant, simply compare the hardware and software implementations'
results.

While we're at it, also log the resulting decision at DEBUG1, and error
out if the hw and sw results unexpectedly differ.  Also, since this
file must compile for both frontend and backend, avoid incorrect
dependencies on backend-only headers.

In passing, add a comment to postmaster.c about when the CRC function
pointer will get initialized.

Thomas Munro, based on complaints from Andrew Gierth and Tom Lane

Discussion: https://postgr.es/m/HE1PR0801MB1323D171938EABC04FFE7FA9E3110@HE1PR0801MB1323.eurprd08.prod.outlook.com

diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index d948369f3eaaf27bd6020f62d11a519e4710f9ae..a4b53b33cdde912cc0d4639d8c7d27c0ae6693de 100644 (file)
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -957,7 +957,15 @@ PostmasterMain(int argc, char *argv[])
         */
        CreateDataDirLockFile(true);
 
-       /* read control file (error checking and contains config) */
+       /*
+        * Read the control file (for error checking and config info).
+        *
+        * Since we verify the control file's CRC, this has a useful side effect
+        * on machines where we need a run-time test for CRC support instructions.
+        * The postmaster will do the test once at startup, and then its child
+        * processes will inherit the correct function pointer and not need to
+        * repeat the test.
+        */
        LocalProcessControlFile(false);
 
        /*

diff --git a/src/port/pg_crc32c_armv8_choose.c b/src/port/pg_crc32c_armv8_choose.c
index d0d3a3da78ed9bfcc48794a6d69462b6fc7daa5f..c339af7f16a00a6796d8fdf5ffd1e73744865f54 100644 (file)
--- a/src/port/pg_crc32c_armv8_choose.c
+++ b/src/port/pg_crc32c_armv8_choose.c
@@ -18,11 +18,15 @@
  *-------------------------------------------------------------------------
  */
 
-#include "c.h"
+#ifndef FRONTEND
+#include "postgres.h"
+#else
+#include "postgres_fe.h"
+#endif
 
 #include <setjmp.h>
+#include <signal.h>
 
-#include "libpq/pqsignal.h"
 #include "port/pg_crc32c.h"
 
 
@@ -33,7 +37,7 @@ static sigjmp_buf illegal_instruction_jump;
  * isn't available, we expect to get SIGILL, which we can trap.
  */
 static void
-illegal_instruction_handler(int signo)
+illegal_instruction_handler(SIGNAL_ARGS)
 {
        siglongjmp(illegal_instruction_jump, 1);
 }
@@ -42,16 +46,35 @@ static bool
 pg_crc32c_armv8_available(void)
 {
        uint64          data = 42;
-       bool            result;
+       int                     result;
 
+       /*
+        * Be careful not to do anything that might throw an error while we have
+        * the SIGILL handler set to a nonstandard value.
+        */
        pqsignal(SIGILL, illegal_instruction_handler);
        if (sigsetjmp(illegal_instruction_jump, 1) == 0)
-               result = (pg_comp_crc32c_armv8(0, &data, sizeof(data)) == 0xdd439b0d);
+       {
+               /* Rather than hard-wiring an expected result, compare to SB8 code */
+               result = (pg_comp_crc32c_armv8(0, &data, sizeof(data)) ==
+                                 pg_comp_crc32c_sb8(0, &data, sizeof(data)));
+       }
        else
-               result = false;
+       {
+               /* We got the SIGILL trap */
+               result = -1;
+       }
        pqsignal(SIGILL, SIG_DFL);
 
-       return result;
+#ifndef FRONTEND
+       /* We don't expect this case, so complain loudly */
+       if (result == 0)
+               elog(ERROR, "crc32 hardware and software results disagree");
+
+       elog(DEBUG1, "using armv8 crc32 hardware = %d", (result > 0));
+#endif
+
+       return (result > 0);
 }
 
 /*