From 9e82eb57870ec7c01734b44ed4bb994362004df3 Mon Sep 17 00:00:00 2001
From: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Date: Fri, 27 Dec 2019 10:20:53 +0100
Subject: [PATCH] CMakeLists.txt: check for atomic library

On some architectures, atomic binutils are provided by the libatomic
library from gcc. Linking with libatomic is therefore necessary,
otherwise the build fails with:

[100%] Linking CXX executable leveldbutil
/home/fabrice/buildroot/output/host/opt/ext-toolchain/bin/../lib/gcc/sparc-buildroot-linux-uclibc/7.4.0/../../../../sparc-buildroot-linux-uclibc/bin/ld: libleveldb.a(env_posix.cc.o): in function `leveldb::(anonymous namespace)::Limiter::Acquire()':
env_posix.cc:(.text+0x124): undefined reference to `__atomic_fetch_sub_4'

This is often for example the case on sparcv8 32 bit.

Fixes:
 - http://autobuild.buildroot.org/results/01d5a50581ac9e9b46f40e6f9665f74897db5e6f

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
[Upstream status: https://github.com/google/leveldb/pull/765]
---
 CMakeLists.txt | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index be41ba4..9d6773f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -41,6 +41,7 @@ include(CheckIncludeFile)
 check_include_file("unistd.h" HAVE_UNISTD_H)
 
 include(CheckLibraryExists)
+check_library_exists(atomic __atomic_fetch_add_4 "" HAVE_ATOMIC)
 check_library_exists(crc32c crc32c_value "" HAVE_CRC32C)
 check_library_exists(snappy snappy_compress "" HAVE_SNAPPY)
 check_library_exists(tcmalloc malloc "" HAVE_TCMALLOC)
@@ -270,6 +271,9 @@ if(HAVE_CLANG_THREAD_SAFETY)
       -Werror -Wthread-safety)
 endif(HAVE_CLANG_THREAD_SAFETY)
 
+if(HAVE_ATOMIC)
+  target_link_libraries(leveldb atomic)
+endif(HAVE_ATOMIC)
 if(HAVE_CRC32C)
   target_link_libraries(leveldb crc32c)
 endif(HAVE_CRC32C)
-- 
2.24.0