bitcoin/build-aux/m4/l_atomic.m4
Andrew Chow 4de4221ab4 build: Check for std::atomic::exchange rather than std::atomic_exchange
Our usage of std::atomic is with it's own exchange function, not
std::atomic_exchange. So we should be looking specifically for that
function.

Additionally, -pthread and -lpthread have an effect on whether -latomic
will be needed, so the atomics check needs to use these flags as well.
This will make the flags in use better match what is actually used when
linking.

This removes the need for -latomic for riscv builds, which resolves a
guix cross architecture reproducibility issue.
2022-07-18 10:47:19 -04:00

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dnl Copyright (c) 2015 Tim Kosse <tim.kosse@filezilla-project.org>
dnl Copying and distribution of this file, with or without modification, are
dnl permitted in any medium without royalty provided the copyright notice
dnl and this notice are preserved. This file is offered as-is, without any
dnl warranty.
# Some versions of gcc/libstdc++ require linking with -latomic if
# using the C++ atomic library.
#
# Sourced from http://bugs.debian.org/797228
m4_define([_CHECK_ATOMIC_testbody], [[
#include <atomic>
#include <cstdint>
#include <chrono>
using namespace std::chrono_literals;
int main() {
std::atomic<bool> lock{true};
lock.exchange(false);
std::atomic<std::chrono::seconds> t{0s};
t.store(2s);
std::atomic<int64_t> a{};
int64_t v = 5;
int64_t r = a.fetch_add(v);
return static_cast<int>(r);
}
]])
AC_DEFUN([CHECK_ATOMIC], [
AC_LANG_PUSH(C++)
TEMP_CXXFLAGS="$CXXFLAGS"
CXXFLAGS="$CXXFLAGS $PTHREAD_CFLAGS"
AC_MSG_CHECKING([whether std::atomic can be used without link library])
AC_LINK_IFELSE([AC_LANG_SOURCE([_CHECK_ATOMIC_testbody])],[
AC_MSG_RESULT([yes])
],[
AC_MSG_RESULT([no])
LIBS="$LIBS -latomic"
AC_MSG_CHECKING([whether std::atomic needs -latomic])
AC_LINK_IFELSE([AC_LANG_SOURCE([_CHECK_ATOMIC_testbody])],[
AC_MSG_RESULT([yes])
],[
AC_MSG_RESULT([no])
AC_MSG_FAILURE([cannot figure out how to use std::atomic])
])
])
CXXFLAGS="$TEMP_CXXFLAGS"
AC_LANG_POP
])