Use auxv to check for CRC32 instructions on ARM.

Previously we probed for CRC32 instructions by testing if they caused
SIGILL.  Some have expressed doubts about that technique, the Linux
documentation advises not to use it, and it's not exactly beautiful.
Now that more operating systems expose CPU features to userspace via the
ELF loader in approximately the same way, let's use that instead.

This is expected to work on Linux, FreeBSD and recent OpenBSD.
OpenBSD/ARM has not been tested and is not present in our build farm,
but the API matches FreeBSD.

On macOS, compilers use a more recent baseline ISA so the runtime test
mechanism isn't reached.  (A similar situation is expected for
Windows/ARM when that port lands.)

On NetBSD, runtime feature probing is lost for armv8-a builds.  It looks
potentially doable with sysctl following the example of the cpuctl
program; es are welcome.

No back- for now, since we don't have any evidence of actual
breakage from the previous technique.

Suggested-by: Bastien Roucariès <[email protected]>
Discussion: https://postgr.es/m/4496616.iHFcN1HehY%40portable-bastien

diff --git a/configure b/configure
index bb67e5fcda46713a2598288f04e71f775615a91a..28719ed30c661cb5630991e7871639a2e2bd7e20 100755 (executable)
--- a/configure
+++ b/configure
@@ -15144,7 +15144,7 @@ fi
 LIBS_including_readline="$LIBS"
 LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
 
-for ac_func in backtrace_symbols copyfile copy_file_range getifaddrs getpeerucred inet_pton kqueue mbstowcs_l memset_s posix_fallocate ppoll pthread_is_threaded_np setproctitle setproctitle_fast strchrnul strsignal syncfs sync_file_range uselocale wcstombs_l
+for ac_func in backtrace_symbols copyfile copy_file_range elf_aux_info getauxval getifaddrs getpeerucred inet_pton kqueue mbstowcs_l memset_s posix_fallocate ppoll pthread_is_threaded_np setproctitle setproctitle_fast strchrnul strsignal syncfs sync_file_range uselocale wcstombs_l
 do :
   as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
 ac_fn_c_check_func "$LINENO" "$ac_func" "$as_ac_var"

diff --git a/configure.ac b/configure.ac
index 12136261347f60ccf4d739eeae8a396b54f41448..533f4ab78a5f9e48e2e831ad4a6a2a7cb67e85aa 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -1723,6 +1723,8 @@ AC_CHECK_FUNCS(m4_normalize([
    backtrace_symbols
    copyfile
    copy_file_range
+   elf_aux_info
+   getauxval
    getifaddrs
    getpeerucred
    inet_pton

diff --git a/meson.build b/meson.build
index 5b0510cef78b8d1a66627528f77a03c68d919829..b64d253fe41c2c240979258af0f7d7bd14c1610a 100644 (file)
--- a/meson.build
+++ b/meson.build
@@ -2623,7 +2623,9 @@ func_checks = [
   # when enabling asan the dlopen check doesn't notice that -ldl is actually
   # required. Just checking for dlsym() ought to suffice.
   ['dlsym', {'dependencies': [dl_dep], 'define': false}],
+  ['elf_aux_info'],
   ['explicit_bzero'],
+  ['getauxval'],
   ['getifaddrs'],
   ['getopt', {'dependencies': [getopt_dep, gnugetopt_dep], 'skip': always_replace_getopt}],
   ['getopt_long', {'dependencies': [getopt_dep, gnugetopt_dep], 'skip': always_replace_getopt_long}],

diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index cdd9a6e935549754762a8a7915206ca321bb9fa8..a903c60a3a0bb6628a7c21e583ba0e90eda49c1a 100644 (file)
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -125,6 +125,9 @@
 /* Define to 1 if you have the <editline/readline.h> header file. */
 #undef HAVE_EDITLINE_READLINE_H
 
+/* Define to 1 if you have the `elf_aux_info' function. */
+#undef HAVE_ELF_AUX_INFO
+
 /* Define to 1 if you have the <execinfo.h> header file. */
 #undef HAVE_EXECINFO_H
 
@@ -154,6 +157,9 @@
    */
 #undef HAVE_GCC__SYNC_INT64_CAS
 
+/* Define to 1 if you have the `getauxval' function. */
+#undef HAVE_GETAUXVAL
+
 /* Define to 1 if you have the `getifaddrs' function. */
 #undef HAVE_GETIFADDRS
 

diff --git a/src/port/pg_crc32c_armv8_choose.c b/src/port/pg_crc32c_armv8_choose.c
index eaf39cf3e8176c619fa2983dca9caf7d8f27d934..306500154ee62f51e9adf6d0ec499cfea48e0867 100644 (file)
--- a/src/port/pg_crc32c_armv8_choose.c
+++ b/src/port/pg_crc32c_armv8_choose.c
@@ -24,57 +24,37 @@
 #include "postgres_fe.h"
 #endif
 
-#include <setjmp.h>
-#include <signal.h>
+#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
 
 #include "port/pg_crc32c.h"
 
-
-static sigjmp_buf illegal_instruction_jump;
-
-/*
- * Probe by trying to execute pg_comp_crc32c_armv8().  If the instruction
- * isn't available, we expect to get SIGILL, which we can trap.
- */
-static void
-illegal_instruction_handler(SIGNAL_ARGS)
-{
-   siglongjmp(illegal_instruction_jump, 1);
-}
-
 static bool
 pg_crc32c_armv8_available(void)
 {
-   uint64      data = 42;
-   int         result;
+#if defined(HAVE_ELF_AUX_INFO)
+   unsigned long value;
 
-   /*
-    * 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)
-   {
-       /* 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
-   {
-       /* We got the SIGILL trap */
-       result = -1;
-   }
-   pqsignal(SIGILL, SIG_DFL);
-
-#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));
+#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
+#else
+   return false;
 #endif
-
-   return (result > 0);
 }
 
 /*