From: Alexander Graf <agraf@suse.de>
Date: Mon, 26 Sep 2016 08:26:30 +0000 (+0200)
Subject: AArch64: Detect crc32 extension support from assembler
X-Git-Tag: v10.2.4~37^2
X-Git-Url: http://git.apps.os.sepia.ceph.com/?a=commitdiff_plain;h=91bd342df6de15263004f3a41c285f6658a16d45;p=ceph.git

AArch64: Detect crc32 extension support from assembler

The used compiler may or may not be recent enough to recognize the
crc32 extended cpu type. However, it does not really have to know about
them either, since all we do is pass inline assembly instructions to
the assembler.

This patch moves the crc cpu extension detection from compiler based
to assembler based, so that we can build optimized code even when the
compiler does not know about the cpu type yet.

Signed-off-by: Alexander Graf <agraf@suse.de>

(manual backport of e70ab48b7f6d39a281b3ec65098535a55018b681 - manual backport
was undertaken because jewel uses autotools)
---

diff --git a/m4/ax_arm.m4 b/m4/ax_arm.m4
index 37ea0aaf1d16a..26b5258bd6f96 100644
--- a/m4/ax_arm.m4
+++ b/m4/ax_arm.m4
@@ -26,12 +26,19 @@ AC_DEFUN([AX_ARM_FEATURES],
         AC_DEFINE(HAVE_NEON,,[Support NEON instructions])
         AC_SUBST(ARM_NEON_FLAGS)
       fi
-      AX_CHECK_COMPILE_FLAG(-march=armv8-a+crc, ax_cv_support_crc_ext=yes, [])
+
+      AC_LANG_SAVE
+      AC_LANG_CPLUSPLUS
+      AC_CACHE_CHECK(whether the assembler supports crc extensions,
+                     ax_cv_support_crc_ext, AC_TRY_COMPILE([
+          #define CRC32CX(crc, value) __asm__("crc32cx %w[c], %w[c], %x[v]":[c]"+r"(crc):[v]"r"(value))
+          asm(".arch_extension crc");
+          unsigned int foo(unsigned int ret) {
+              CRC32CX(ret, 0);
+              return ret;
+          }],[ foo(0); ], ax_cv_support_crc_ext=yes, []))
       if test x"$ax_cv_support_crc_ext" = x"yes"; then
-        ARM_ARCH_FLAGS="$ARM_ARCH_FLAGS+crc"
-        ARM_CRC_FLAGS="-march=armv8-a+crc -DARCH_AARCH64"
         AC_DEFINE(HAVE_ARMV8_CRC,,[Support ARMv8 CRC instructions])
-        AC_SUBST(ARM_CRC_FLAGS)
       fi
         ARM_FLAGS="$ARM_ARCH_FLAGS $ARM_DEFINE_FLAGS"
     ;;
diff --git a/src/common/Makefile.am b/src/common/Makefile.am
index 8b30eeadec17d..e92e51c09900e 100644
--- a/src/common/Makefile.am
+++ b/src/common/Makefile.am
@@ -144,7 +144,7 @@ noinst_LTLIBRARIES += libcommon_crc.la
 
 if HAVE_ARMV8_CRC
 libcommon_crc_aarch64_la_SOURCES = common/crc32c_aarch64.c
-libcommon_crc_aarch64_la_CFLAGS = $(AM_CFLAGS) $(ARM_CRC_FLAGS)
+libcommon_crc_aarch64_la_CFLAGS = $(AM_CFLAGS) $(ARM_ARCH_FLAGS)
 LIBCOMMON_DEPS += libcommon_crc_aarch64.la
 noinst_LTLIBRARIES += libcommon_crc_aarch64.la
 endif
diff --git a/src/common/crc32c_aarch64.c b/src/common/crc32c_aarch64.c
index d33827d9e9886..d2be6ddd85a76 100644
--- a/src/common/crc32c_aarch64.c
+++ b/src/common/crc32c_aarch64.c
@@ -2,6 +2,9 @@
 #include "include/int_types.h"
 #include "common/crc32c_aarch64.h"
 
+/* Request crc extension capabilities from the assembler */
+asm(".arch_extension crc");
+
 #define CRC32CX(crc, value) __asm__("crc32cx %w[c], %w[c], %x[v]":[c]"+r"(crc):[v]"r"(value))
 #define CRC32CW(crc, value) __asm__("crc32cw %w[c], %w[c], %w[v]":[c]"+r"(crc):[v]"r"(value))
 #define CRC32CH(crc, value) __asm__("crc32ch %w[c], %w[c], %w[v]":[c]"+r"(crc):[v]"r"(value))