From e70ab48b7f6d39a281b3ec65098535a55018b681 Mon Sep 17 00:00:00 2001
From: Alexander Graf <agraf@suse.de>
Date: Mon, 26 Sep 2016 16:26:37 +0200
Subject: [PATCH] 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.

Fixes: http://tracker.ceph.com/issues/17516
Signed-off-by: Alexander Graf <agraf@suse.de>
---
 cmake/modules/SIMDExt.cmake | 15 +++++++++++++--
 src/CMakeLists.txt          |  1 -
 src/common/crc32c_aarch64.c |  3 +++
 3 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/cmake/modules/SIMDExt.cmake b/cmake/modules/SIMDExt.cmake
index c531d8ca2f2..a984b51e689 100644
--- a/cmake/modules/SIMDExt.cmake
+++ b/cmake/modules/SIMDExt.cmake
@@ -16,9 +16,20 @@
 
 if(CMAKE_SYSTEM_PROCESSOR MATCHES "aarch64|AARCH64")
   set(HAVE_ARM 1) 
-  CHECK_C_COMPILER_FLAG(-march=armv8-a+crc HAVE_ARMV8_CRC)
+  set(save_quiet ${CMAKE_REQUIRED_QUIET})
+  set(CMAKE_REQUIRED_QUIET true)
+  include(CheckCXXSourceCompiles)
+  check_cxx_source_compiles("
+    #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;
+    }
+    int main() { foo(0); }" HAVE_ARMV8_CRC)
+  set(CMAKE_REQUIRED_QUIET ${save_quiet})
   if(HAVE_ARMV8_CRC)
-    set(ARM_CRC_FLAGS "-march=armv8-a+crc")
+    message(STATUS " aarch64 crc extensions supported")
   endif()
   CHECK_C_COMPILER_FLAG(-march=armv8-a+simd HAVE_ARMV8_SIMD)
   if(HAVE_ARMV8_SIMD)
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index caab0a37cd3..829aea8e2f9 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -488,7 +488,6 @@ set_source_files_properties(${CMAKE_SOURCE_DIR}/src/ceph_ver.c
 include(SIMDExt)
 if(HAVE_ARMV8_CRC)
   add_library(common_crc_aarch64 STATIC common/crc32c_aarch64.c)
-  set_target_properties(common_crc_aarch64 PROPERTIES COMPILE_FLAGS "${CMAKE_C_FLAGS} ${ARM_CRC_FLAGS}")
   target_link_libraries(common common_crc_aarch64)
 endif(HAVE_ARMV8_CRC)
 
diff --git a/src/common/crc32c_aarch64.c b/src/common/crc32c_aarch64.c
index d33827d9e98..d2be6ddd85a 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))
-- 
2.47.3