configure.ac

dnl Copyright (c) 2001-2004, Roger Dingledine
dnl Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson
dnl Copyright (c) 2007-2017, The Tor Project, Inc.
dnl See LICENSE for licensing information

AC_PREREQ([2.63])
AC_INIT([tor],[0.3.3.4-alpha-dev])
AC_CONFIG_SRCDIR([src/or/main.c])
AC_CONFIG_MACRO_DIR([m4])

# "foreign" means we don't follow GNU package layout standards
# "1.11" means we require automake version 1.11 or newer
# "subdir-objects" means put .o files in the same directory as the .c files
AM_INIT_AUTOMAKE([foreign 1.11 subdir-objects -Wall -Werror])

m4_ifdef([AM_SILENT_RULES], [AM_SILENT_RULES([yes])])
AC_CONFIG_HEADERS([orconfig.h])

AC_USE_SYSTEM_EXTENSIONS
AC_CANONICAL_HOST

PKG_PROG_PKG_CONFIG

if test -f "/etc/redhat-release"; then
  if test -f "/usr/kerberos/include"; then
    CPPFLAGS="$CPPFLAGS -I/usr/kerberos/include"
  fi
fi

# Not a no-op; we want to make sure that CPPFLAGS is set before we use
# the += operator on it in src/or/Makefile.am
CPPFLAGS="$CPPFLAGS -I\${top_srcdir}/src/common"

AC_ARG_ENABLE(openbsd-malloc,
   AS_HELP_STRING(--enable-openbsd-malloc, [use malloc code from OpenBSD.  Linux only]))
AC_ARG_ENABLE(static-openssl,
   AS_HELP_STRING(--enable-static-openssl, [link against a static openssl library. Requires --with-openssl-dir]))
AC_ARG_ENABLE(static-libevent,
   AS_HELP_STRING(--enable-static-libevent, [link against a static libevent library. Requires --with-libevent-dir]))
AC_ARG_ENABLE(static-zlib,
   AS_HELP_STRING(--enable-static-zlib, [link against a static zlib library. Requires --with-zlib-dir]))
AC_ARG_ENABLE(static-tor,
   AS_HELP_STRING(--enable-static-tor, [create an entirely static Tor binary. Requires --with-openssl-dir and --with-libevent-dir and --with-zlib-dir]))
AC_ARG_ENABLE(unittests,
   AS_HELP_STRING(--disable-unittests, [don't build unit tests for Tor. Risky!]))
AC_ARG_ENABLE(coverage,
   AS_HELP_STRING(--enable-coverage, [enable coverage support in the unit-test build]))
AC_ARG_ENABLE(asserts-in-tests,
   AS_HELP_STRING(--disable-asserts-in-tests, [disable tor_assert() calls in the unit tests, for branch coverage]))
AC_ARG_ENABLE(system-torrc,
   AS_HELP_STRING(--disable-system-torrc, [don't look for a system-wide torrc file]))
AC_ARG_ENABLE(libfuzzer,
   AS_HELP_STRING(--enable-libfuzzer, [build extra fuzzers based on 'libfuzzer']))
AC_ARG_ENABLE(oss-fuzz,
   AS_HELP_STRING(--enable-oss-fuzz, [build extra fuzzers based on 'oss-fuzz' environment]))
AC_ARG_ENABLE(memory-sentinels,
   AS_HELP_STRING(--disable-memory-sentinels, [disable code that tries to prevent some kinds of memory access bugs. For fuzzing only.]))
AC_ARG_ENABLE(rust,
   AS_HELP_STRING(--enable-rust, [enable rust integration]))
AC_ARG_ENABLE(cargo-online-mode,
   AS_HELP_STRING(--enable-cargo-online-mode, [Allow cargo to make network requests to fetch crates. For builds with rust only.]))
AC_ARG_ENABLE(restart-debugging,
   AS_HELP_STRING(--enable-restart-debugging, [Build Tor with support for debugging in-process restart. Developers only.]))

if test "x$enable_coverage" != "xyes" -a "x$enable_asserts_in_tests" = "xno" ; then
    AC_MSG_ERROR([Can't disable assertions outside of coverage build])
fi

AM_CONDITIONAL(UNITTESTS_ENABLED, test "x$enable_unittests" != "xno")
AM_CONDITIONAL(COVERAGE_ENABLED, test "x$enable_coverage" = "xyes")
AM_CONDITIONAL(DISABLE_ASSERTS_IN_UNIT_TESTS, test "x$enable_asserts_in_tests" = "xno")
AM_CONDITIONAL(LIBFUZZER_ENABLED, test "x$enable_libfuzzer" = "xyes")
AM_CONDITIONAL(OSS_FUZZ_ENABLED, test "x$enable_oss_fuzz" = "xyes")
AM_CONDITIONAL(USE_RUST, test "x$enable_rust" = "xyes")

if test "$enable_static_tor" = "yes"; then
  enable_static_libevent="yes";
  enable_static_openssl="yes";
  enable_static_zlib="yes";
  CFLAGS="$CFLAGS -static"
fi

if test "$enable_system_torrc" = "no"; then
  AC_DEFINE(DISABLE_SYSTEM_TORRC, 1,
            [Defined if we're not going to look for a torrc in SYSCONF])
fi

if test "$enable_memory_sentinels" = "no"; then
  AC_DEFINE(DISABLE_MEMORY_SENTINELS, 1,
           [Defined if we're turning off memory safety code to look for bugs])
fi

AM_CONDITIONAL(USE_OPENBSD_MALLOC, test "x$enable_openbsd_malloc" = "xyes")

AC_ARG_ENABLE(asciidoc,
     AS_HELP_STRING(--disable-asciidoc, [don't use asciidoc (disables building of manpages)]),
     [case "${enableval}" in
        "yes") asciidoc=true ;;
        "no")  asciidoc=false ;;
        *) AC_MSG_ERROR(bad value for --disable-asciidoc) ;;
      esac], [asciidoc=true])

# systemd notify support
AC_ARG_ENABLE(systemd,
      AS_HELP_STRING(--enable-systemd, [enable systemd notification support]),
      [case "${enableval}" in
        "yes") systemd=true ;;
        "no")  systemd=false ;;
        * ) AC_MSG_ERROR(bad value for --enable-systemd) ;;
      esac], [systemd=auto])

if test "$enable_restart_debugging" = "yes"; then
  AC_DEFINE(ENABLE_RESTART_DEBUGGING, 1,
            [Defined if we're building with support for in-process restart debugging.])
fi


# systemd support
if test "x$enable_systemd" = "xno"; then
    have_systemd=no;
else
    PKG_CHECK_MODULES(SYSTEMD,
        [libsystemd-daemon],
        have_systemd=yes,
        have_systemd=no)
    if test "x$have_systemd" = "xno"; then
        AC_MSG_NOTICE([Okay, checking for systemd a different way...])
        PKG_CHECK_MODULES(SYSTEMD,
            [libsystemd],
            have_systemd=yes,
            have_systemd=no)
    fi
fi

if test "x$have_systemd" = "xyes"; then
    AC_DEFINE(HAVE_SYSTEMD,1,[Have systemd])
    TOR_SYSTEMD_CFLAGS="${SYSTEMD_CFLAGS}"
    TOR_SYSTEMD_LIBS="${SYSTEMD_LIBS}"
    PKG_CHECK_MODULES(LIBSYSTEMD209, [libsystemd >= 209],
         [AC_DEFINE(HAVE_SYSTEMD_209,1,[Have systemd v209 or more])], [])
fi
AC_SUBST(TOR_SYSTEMD_CFLAGS)
AC_SUBST(TOR_SYSTEMD_LIBS)

if test "x$enable_systemd" = "xyes" -a "x$have_systemd" != "xyes" ; then
    AC_MSG_ERROR([Explicitly requested systemd support, but systemd not found])
fi

case "$host" in
   *-*-solaris* )
     AC_DEFINE(_REENTRANT, 1, [Define on some platforms to activate x_r() functions in time.h])
     ;;
esac

AC_ARG_ENABLE(gcc-warnings,
     AS_HELP_STRING(--enable-gcc-warnings, [deprecated alias for enable-fatal-warnings]))
AC_ARG_ENABLE(fatal-warnings,
     AS_HELP_STRING(--enable-fatal-warnings, [tell the compiler to treat all warnings as errors.]))
AC_ARG_ENABLE(gcc-warnings-advisory,
     AS_HELP_STRING(--disable-gcc-warnings-advisory, [disable the regular verbose warnings]))

dnl Others suggest '/gs /safeseh /nxcompat /dynamicbase' for non-gcc on Windows
AC_ARG_ENABLE(gcc-hardening,
    AS_HELP_STRING(--disable-gcc-hardening, [disable compiler security checks]))

dnl Deprecated --enable-expensive-hardening but keep it for now for backward compat.
AC_ARG_ENABLE(expensive-hardening,
    AS_HELP_STRING(--enable-expensive-hardening, [enable more fragile and expensive compiler hardening; makes Tor slower]))
AC_ARG_ENABLE(fragile-hardening,
    AS_HELP_STRING(--enable-fragile-hardening, [enable more fragile and expensive compiler hardening; makes Tor slower]))
if test "x$enable_expensive_hardening" = "xyes" || test "x$enable_fragile_hardening" = "xyes"; then
  fragile_hardening="yes"
fi

dnl Linker hardening options
dnl Currently these options are ELF specific - you can't use this with MacOSX
AC_ARG_ENABLE(linker-hardening,
    AS_HELP_STRING(--disable-linker-hardening, [disable linker security fixups]))

AC_ARG_ENABLE(local-appdata,
   AS_HELP_STRING(--enable-local-appdata, [default to host local application data paths on Windows]))
if test "$enable_local_appdata" = "yes"; then
  AC_DEFINE(ENABLE_LOCAL_APPDATA, 1,
            [Defined if we default to host local appdata paths on Windows])
fi

# Tor2web mode flag
AC_ARG_ENABLE(tor2web-mode,
     AS_HELP_STRING(--enable-tor2web-mode, [support tor2web non-anonymous mode]),
[if test "x$enableval" = "xyes"; then
    CFLAGS="$CFLAGS -D ENABLE_TOR2WEB_MODE=1"
fi])

AC_ARG_ENABLE(tool-name-check,
     AS_HELP_STRING(--disable-tool-name-check, [check for sanely named toolchain when cross-compiling]))

AC_ARG_ENABLE(seccomp,
     AS_HELP_STRING(--disable-seccomp, [do not attempt to use libseccomp]))

AC_ARG_ENABLE(libscrypt,
     AS_HELP_STRING(--disable-libscrypt, [do not attempt to use libscrypt]))

dnl Enable event tracing which are transformed to debug log statement.
AC_ARG_ENABLE(event-tracing-debug,
     AS_HELP_STRING(--enable-event-tracing-debug, [build with event tracing to debug log]))
AM_CONDITIONAL([USE_EVENT_TRACING_DEBUG], [test "x$enable_event_tracing_debug" = "xyes"])

if test x$enable_event_tracing_debug = xyes; then
  AC_DEFINE([USE_EVENT_TRACING_DEBUG], [1], [Tracing framework to log debug])
  AC_DEFINE([TOR_EVENT_TRACING_ENABLED], [1], [Compile the event tracing instrumentation])
fi

dnl Enable Android only features.
AC_ARG_ENABLE(android,
     AS_HELP_STRING(--enable-android, [build with Android features enabled]))
AM_CONDITIONAL([USE_ANDROID], [test "x$enable_android" = "xyes"])

if test "x$enable_android" = "xyes"; then
  AC_DEFINE([USE_ANDROID], [1], [Compile with Android specific features enabled])

  dnl Check if the Android log library is available.
  AC_CHECK_HEADERS([android/log.h])
  AC_SEARCH_LIBS(__android_log_write, [log])

fi

dnl check for the correct "ar" when cross-compiling.
dnl   (AM_PROG_AR was new in automake 1.11.2, which we do not yet require,
dnl    so kludge up a replacement for the case where it isn't there yet.)
m4_ifdef([AM_PROG_AR],
         [AM_PROG_AR],
         [AN_MAKEVAR([AR], [AC_PROG_AR])
          AN_PROGRAM([ar], [AC_PROG_AR])
          AC_DEFUN([AC_PROG_AR], [AC_CHECK_TOOL([AR], [ar], [:])])
          AC_PROG_AR])

dnl Check whether the above macro has settled for a simply named tool even
dnl though we're cross compiling. We must do this before running AC_PROG_CC,
dnl because that will find any cc on the system, not only the cross-compiler,
dnl and then verify that a binary built with this compiler runs on the
dnl build system. It will then come to the false conclusion that we're not
dnl cross-compiling.
if test "x$enable_tool_name_check" != "xno"; then
    if test "x$ac_tool_warned" = "xyes"; then
        AC_MSG_ERROR([We are cross compiling but could not find a properly named toolchain. Do you have your cross-compiling toolchain in PATH? (You can --disable-tool-name-check to ignore this.)])
	elif test "x$ac_ct_AR" != "x" -a "x$cross_compiling" = "xmaybe"; then
		AC_MSG_ERROR([We think we are cross compiling but could not find a properly named toolchain. Do you have your cross-compiling toolchain in PATH? (You can --disable-tool-name-check to ignore this.)])
	fi
fi

AC_PROG_CC
AC_PROG_CPP
AC_PROG_MAKE_SET
AC_PROG_RANLIB
AC_PROG_SED

AC_ARG_VAR([PERL], [path to Perl binary])
AC_CHECK_PROGS([PERL], [perl])
AM_CONDITIONAL(USE_PERL, [test "x$ac_cv_prog_PERL" != "x"])

dnl check for asciidoc and a2x
AC_PATH_PROG([ASCIIDOC], [asciidoc], none)
AC_PATH_PROGS([A2X], [a2x a2x.py], none)

AM_CONDITIONAL(USE_ASCIIDOC, test "x$asciidoc" = "xtrue")

AM_PROG_CC_C_O
AC_PROG_CC_C99

AC_ARG_VAR([PYTHON], [path to Python binary])
AC_CHECK_PROGS(PYTHON, [python python2 python2.7 python3 python3.3])
if test "x$PYTHON" = "x"; then
  AC_MSG_WARN([Python unavailable; some tests will not be run.])
fi
AM_CONDITIONAL(USEPYTHON, [test "x$PYTHON" != "x"])

dnl List all external rust crates we depend on here. Include the version
rust_crates="libc-0.2.39"
AC_SUBST(rust_crates)

ifdef([AC_C_FLEXIBLE_ARRAY_MEMBER], [
AC_C_FLEXIBLE_ARRAY_MEMBER
], [
 dnl Maybe we've got an old autoconf...
 AC_CACHE_CHECK([for flexible array members],
     tor_cv_c_flexarray,
     [AC_COMPILE_IFELSE(
       AC_LANG_PROGRAM([
 struct abc { int a; char b[]; };
], [
 struct abc *def = malloc(sizeof(struct abc)+sizeof(char));
 def->b[0] = 33;
]),
  [tor_cv_c_flexarray=yes],
  [tor_cv_c_flexarray=no])])
 if test "$tor_cv_flexarray" = "yes"; then
   AC_DEFINE([FLEXIBLE_ARRAY_MEMBER], [], [Define to nothing if C supports flexible array members, and to 1 if it does not.])
 else
   AC_DEFINE([FLEXIBLE_ARRAY_MEMBER], [1], [Define to nothing if C supports flexible array members, and to 1 if it does not.])
 fi
])

AC_CACHE_CHECK([for working C99 mid-block declaration syntax],
      tor_cv_c_c99_decl,
      [AC_COMPILE_IFELSE(
         [AC_LANG_PROGRAM([], [int x; x = 3; int y; y = 4 + x;])],
	 [tor_cv_c_c99_decl=yes],
	 [tor_cv_c_c99_decl=no] )])
if test "$tor_cv_c_c99_decl" != "yes"; then
  AC_MSG_ERROR([Your compiler doesn't support c99 mid-block declarations. This is required as of Tor 0.2.6.x])
fi

AC_CACHE_CHECK([for working C99 designated initializers],
      tor_cv_c_c99_designated_init,
      [AC_COMPILE_IFELSE(
         [AC_LANG_PROGRAM([struct s { int a; int b; };],
  	       [[ struct s ss = { .b = 5, .a = 6 }; ]])],
	 [tor_cv_c_c99_designated_init=yes],
	 [tor_cv_c_c99_designated_init=no] )])

if test "$tor_cv_c_c99_designated_init" != "yes"; then
  AC_MSG_ERROR([Your compiler doesn't support c99 designated initializers. This is required as of Tor 0.2.6.x])
fi

TORUSER=_tor
AC_ARG_WITH(tor-user,
        AS_HELP_STRING(--with-tor-user=NAME, [specify username for tor daemon]),
        [
           TORUSER=$withval
        ]
)
AC_SUBST(TORUSER)

TORGROUP=_tor
AC_ARG_WITH(tor-group,
        AS_HELP_STRING(--with-tor-group=NAME, [specify group name for tor daemon]),
        [
           TORGROUP=$withval
        ]
)
AC_SUBST(TORGROUP)


dnl If _WIN32 is defined and non-zero, we are building for win32
AC_MSG_CHECKING([for win32])
AC_RUN_IFELSE([AC_LANG_SOURCE([
int main(int c, char **v) {
#ifdef _WIN32
#if _WIN32
  return 0;
#else
  return 1;
#endif
#else
  return 2;
#endif
}])],
bwin32=true; AC_MSG_RESULT([yes]),
bwin32=false; AC_MSG_RESULT([no]),
bwin32=cross; AC_MSG_RESULT([cross])
)

if test "$bwin32" = "cross"; then
AC_MSG_CHECKING([for win32 (cross)])
AC_COMPILE_IFELSE([AC_LANG_SOURCE([
#ifdef _WIN32
int main(int c, char **v) {return 0;}
#else
#error
int main(int c, char **v) {return x(y);}
#endif
])],
bwin32=true; AC_MSG_RESULT([yes]),
bwin32=false; AC_MSG_RESULT([no]))
fi

AH_BOTTOM([
#ifdef _WIN32
/* Defined to access windows functions and definitions for >=WinXP */
# ifndef WINVER
#  define WINVER 0x0501
# endif

/* Defined to access _other_ windows functions and definitions for >=WinXP */
# ifndef _WIN32_WINNT
#  define _WIN32_WINNT 0x0501
# endif

/* Defined to avoid including some windows headers as part of Windows.h */
# ifndef WIN32_LEAN_AND_MEAN
#  define WIN32_LEAN_AND_MEAN 1
# endif
#endif
])


AM_CONDITIONAL(BUILD_NT_SERVICES, test "x$bwin32" = "xtrue")
AM_CONDITIONAL(BUILD_LIBTORRUNNER, test "x$bwin32" != "xtrue")

dnl Enable C99 when compiling with MIPSpro
AC_MSG_CHECKING([for MIPSpro compiler])
AC_COMPILE_IFELSE([AC_LANG_PROGRAM(, [
#if (defined(__sgi) && defined(_COMPILER_VERSION))
#error
  return x(y);
#endif
])],
bmipspro=false; AC_MSG_RESULT(no),
bmipspro=true; AC_MSG_RESULT(yes))

if test "$bmipspro" = "true"; then
  CFLAGS="$CFLAGS -c99"
fi

AC_C_BIGENDIAN

if test "x$enable_rust" = "xyes"; then
  AC_ARG_VAR([RUSTC], [path to the rustc binary])
  AC_CHECK_PROG([RUSTC], [rustc], [rustc],[no])
  if test "x$RUSTC" = "xno"; then
    AC_MSG_ERROR([rustc unavailable but rust integration requested.])
  fi

  AC_ARG_VAR([CARGO], [path to the cargo binary])
  AC_CHECK_PROG([CARGO], [cargo], [cargo],[no])
  if test "x$CARGO" = "xno"; then
    AC_MSG_ERROR([cargo unavailable but rust integration requested.])
  fi

  AC_DEFINE([HAVE_RUST], 1, [have Rust])
  if test "x$enable_cargo_online_mode" = "xyes"; then
    CARGO_ONLINE=
    RUST_DL=#
  else
    CARGO_ONLINE=--frozen
    RUST_DL=

    dnl When we're not allowed to touch the network, we need crate dependencies
    dnl locally available.
    AC_MSG_CHECKING([rust crate dependencies])
    AC_ARG_VAR([TOR_RUST_DEPENDENCIES], [path to directory with local crate mirror])
    if test "x$TOR_RUST_DEPENDENCIES" = "x"; then
      TOR_RUST_DEPENDENCIES="$srcdir/src/ext/rust/"
      NEED_MOD=1
    fi
    if test ! -d "$TOR_RUST_DEPENDENCIES"; then
      AC_MSG_ERROR([Rust dependency directory $TOR_RUST_DEPENDENCIES does not exist. Specify a dependency directory using the TOR_RUST_DEPENDENCIES variable or allow cargo to fetch crates using --enable-cargo-online-mode.])
      ERRORED=1
    fi
    for dep in $rust_crates; do
      if test ! -d "$TOR_RUST_DEPENDENCIES"/"$dep"; then
        AC_MSG_ERROR([Failure to find rust dependency $TOR_RUST_DEPENDENCIES/$dep. Specify a dependency directory using the TOR_RUST_DEPENDENCIES variable or allow cargo to fetch crates using --enable-cargo-online-mode.])
        ERRORED=1
      fi
    done
    if test "x$NEED_MOD" = "x1"; then
      dnl When looking for dependencies from cargo, pick right directory
      TOR_RUST_DEPENDENCIES="../../src/ext/rust"
    fi
    if test "x$ERRORED" = "x"; then
      AC_MSG_RESULT([yes])
    fi
  fi

  dnl This is a workaround for #46797
  dnl (a.k.a https://github.com/rust-lang/rust/issues/46797 ).  Once the
  dnl upstream bug is fixed, we can remove this workaround.
  case "$host_os" in
      darwin*)
        TOR_RUST_EXTRA_LIBS="-lresolv"
	;;
  esac

  dnl For now both MSVC and MinGW rust libraries will output static libs with
  dnl the MSVC naming convention.
  if test "$bwin32" = "true"; then
    TOR_RUST_STATIC_NAME=tor_rust.lib
  else
    TOR_RUST_STATIC_NAME=libtor_rust.a
  fi

  AC_SUBST(TOR_RUST_STATIC_NAME)
  AC_SUBST(CARGO_ONLINE)
  AC_SUBST(RUST_DL)

  dnl Let's check the rustc version, too
  AC_MSG_CHECKING([rust version])
  RUSTC_VERSION=`$RUSTC --version`
  RUSTC_VERSION_MAJOR=`$RUSTC --version | cut -d ' ' -f 2 | cut -d '.' -f 1`
  RUSTC_VERSION_MINOR=`$RUSTC --version | cut -d ' ' -f 2 | cut -d '.' -f 2`
  if test "x$RUSTC_VERSION_MAJOR" = "x" -o "x$RUSTC_VERSION_MINOR" = "x"; then
    AC_MSG_ERROR([rustc version couldn't be identified])
  fi
  if test "$RUSTC_VERSION_MAJOR" -lt 2 -a "$RUSTC_VERSION_MINOR" -lt 14; then
    AC_MSG_ERROR([rustc must be at least version 1.14])
  fi
  AC_MSG_RESULT([$RUSTC_VERSION])
fi

AC_SUBST(TOR_RUST_EXTRA_LIBS)

AC_SEARCH_LIBS(socket, [socket network])
AC_SEARCH_LIBS(gethostbyname, [nsl])
AC_SEARCH_LIBS(dlopen, [dl])
AC_SEARCH_LIBS(inet_aton, [resolv])
AC_SEARCH_LIBS(backtrace, [execinfo])
saved_LIBS="$LIBS"
AC_SEARCH_LIBS([clock_gettime], [rt])
if test "$LIBS" != "$saved_LIBS"; then
   # Looks like we need -lrt for clock_gettime().
   have_rt=yes
fi

AC_SEARCH_LIBS(pthread_create, [pthread])
AC_SEARCH_LIBS(pthread_detach, [pthread])

AM_CONDITIONAL(THREADS_WIN32, test "$bwin32" = "true")
AM_CONDITIONAL(THREADS_PTHREADS, test "$bwin32" = "false")

AC_CHECK_FUNCS(
        _NSGetEnviron \
	RtlSecureZeroMemory \
	SecureZeroMemory \
        accept4 \
        backtrace \
        backtrace_symbols_fd \
	eventfd \
	explicit_bzero \
	timingsafe_memcmp \
        flock \
        ftime \
        get_current_dir_name \
        getaddrinfo \
        getifaddrs \
        getpass \
        getrlimit \
        gettimeofday \
        gmtime_r \
	gnu_get_libc_version \
	htonll \
        inet_aton \
        ioctl \
        issetugid \
        llround \
        localtime_r \
        lround \
	mach_approximate_time \
        memmem \
        memset_s \
	pipe \
	pipe2 \
        prctl \
	readpassphrase \
        rint \
        sigaction \
        socketpair \
	statvfs \
        strlcat \
        strlcpy \
	strnlen \
        strptime \
        strtok_r \
        strtoull \
        sysconf \
	sysctl \
	truncate \
        uname \
	usleep \
        vasprintf \
	_vscprintf
)

# Apple messed up when they added two functions functions in Sierra: they
# forgot to decorate them with appropriate AVAILABLE_MAC_OS_VERSION
# checks. So we should only probe for those functions if we are sure that we
# are not targeting OSX 10.11 or earlier.
AC_MSG_CHECKING([for a pre-Sierra OSX build target])
AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
#ifdef __APPLE__
#  include <AvailabilityMacros.h>
#  ifndef MAC_OS_X_VERSION_10_12
#    define MAC_OS_X_VERSION_10_12 101200
#  endif
#  if defined(MAC_OS_X_VERSION_MIN_REQUIRED)
#    if MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_12
#      error "Running on Mac OSX 10.11 or earlier"
#    endif
#  endif
#endif
]], [[]])],
   [on_macos_pre_10_12=no ; AC_MSG_RESULT([no])],
   [on_macos_pre_10_12=yes; AC_MSG_RESULT([yes])])

if test "$on_macos_pre_10_12" = "no"; then
  AC_CHECK_FUNCS(
        clock_gettime \
        getentropy \
  )
fi

if test "$bwin32" != "true"; then
  AC_CHECK_HEADERS(pthread.h)
  AC_CHECK_FUNCS(pthread_create)
  AC_CHECK_FUNCS(pthread_condattr_setclock)
fi

if test "$bwin32" = "true"; then
  AC_CHECK_DECLS([SecureZeroMemory, _getwch], , , [
#include <windows.h>
#include <conio.h>
#include <wchar.h>
                 ])
fi

AM_CONDITIONAL(BUILD_READPASSPHRASE_C,
  test "x$ac_cv_func_readpassphrase" = "xno" && test "$bwin32" = "false")

dnl ------------------------------------------------------
dnl Where do you live, libevent?  And how do we call you?

if test "$bwin32" = "true"; then
  TOR_LIB_WS32=-lws2_32
  TOR_LIB_IPHLPAPI=-liphlpapi
  # Some of the cargo-cults recommend -lwsock32 as well, but I don't
  # think it's actually necessary.
  TOR_LIB_GDI=-lgdi32
  TOR_LIB_USERENV=-luserenv
else
  TOR_LIB_WS32=
  TOR_LIB_GDI=
  TOR_LIB_USERENV=
fi
AC_SUBST(TOR_LIB_WS32)
AC_SUBST(TOR_LIB_GDI)
AC_SUBST(TOR_LIB_IPHLPAPI)
AC_SUBST(TOR_LIB_USERENV)

tor_libevent_pkg_redhat="libevent"
tor_libevent_pkg_debian="libevent-dev"
tor_libevent_devpkg_redhat="libevent-devel"
tor_libevent_devpkg_debian="libevent-dev"

dnl On Gnu/Linux or any place we require it, we'll add librt to the Libevent
dnl linking for static builds.
STATIC_LIBEVENT_FLAGS=""
if test "$enable_static_libevent" = "yes"; then
    if test "$have_rt" = "yes"; then
      STATIC_LIBEVENT_FLAGS=" -lrt "
    fi
fi

TOR_SEARCH_LIBRARY(libevent, $trylibeventdir, [-levent $STATIC_LIBEVENT_FLAGS $TOR_LIB_WS32], [
#ifdef _WIN32
#include <winsock2.h>
#endif
#include <sys/time.h>
#include <sys/types.h>
#include <event2/event.h>], [
#ifdef _WIN32
#include <winsock2.h>
#endif
struct event_base;
struct event_base *event_base_new(void);
void event_base_free(struct event_base *);],
    [
#ifdef _WIN32
{WSADATA d; WSAStartup(0x101,&d); }
#endif
event_base_free(event_base_new());
], [--with-libevent-dir], [/opt/libevent])

dnl Determine the incantation needed to link libevent.
save_LIBS="$LIBS"
save_LDFLAGS="$LDFLAGS"
save_CPPFLAGS="$CPPFLAGS"

LIBS="$STATIC_LIBEVENT_FLAGS $TOR_LIB_WS32 $save_LIBS"
LDFLAGS="$TOR_LDFLAGS_libevent $LDFLAGS"
CPPFLAGS="$TOR_CPPFLAGS_libevent $CPPFLAGS"

AC_CHECK_HEADERS(event2/event.h event2/dns.h event2/bufferevent_ssl.h)

if test "$enable_static_libevent" = "yes"; then
   if test "$tor_cv_library_libevent_dir" = "(system)"; then
     AC_MSG_ERROR("You must specify an explicit --with-libevent-dir=x option when using --enable-static-libevent")
   else
     TOR_LIBEVENT_LIBS="$TOR_LIBDIR_libevent/libevent.a $STATIC_LIBEVENT_FLAGS"
   fi
else
     if test "x$ac_cv_header_event2_event_h" = "xyes"; then
       AC_SEARCH_LIBS(event_new, [event event_core], , AC_MSG_ERROR("libevent2 is installed but linking it failed while searching for event_new"))
       AC_SEARCH_LIBS(evdns_base_new, [event event_extra], , AC_MSG_ERROR("libevent2 is installed but linking it failed while searching for evdns_base_new"))

       if test "$ac_cv_search_event_new" != "none required"; then
         TOR_LIBEVENT_LIBS="$ac_cv_search_event_new"
       fi
       if test "$ac_cv_search_evdns_base_new" != "none required"; then
         TOR_LIBEVENT_LIBS="$ac_cv_search_evdns_base_new $TOR_LIBEVENT_LIBS"
       fi
     else
       AC_MSG_ERROR("libevent2 is required but the headers could not be found")
     fi
fi

dnl Now check for particular libevent functions.
AC_CHECK_FUNCS([evutil_secure_rng_set_urandom_device_file \
                evutil_secure_rng_add_bytes \
])

LIBS="$save_LIBS"
LDFLAGS="$save_LDFLAGS"
CPPFLAGS="$save_CPPFLAGS"

dnl Check that libevent is at least at version 2.0.10, the first stable
dnl release of its series
CPPFLAGS="$CPPFLAGS $TOR_CPPFLAGS_libevent"
AC_MSG_CHECKING([whether Libevent is new enough])
AC_COMPILE_IFELSE([AC_LANG_SOURCE([
#include <event2/event.h>
#if !defined(LIBEVENT_VERSION_NUMBER) || LIBEVENT_VERSION_NUMBER < 0x02000a00
#error
int x = y(zz);
#else
int x = 1;
#endif
])], [ AC_MSG_RESULT([yes]) ],
   [ AC_MSG_RESULT([no])
     AC_MSG_ERROR([Libevent is not new enough.  We require 2.0.10-stable or later]) ] )

LIBS="$save_LIBS"
LDFLAGS="$save_LDFLAGS"
CPPFLAGS="$save_CPPFLAGS"

AC_SUBST(TOR_LIBEVENT_LIBS)

dnl ------------------------------------------------------
dnl Where do you live, libm?

dnl On some platforms (Haiku/BeOS) the math library is
dnl part of libroot. In which case don't link against lm
TOR_LIB_MATH=""
save_LIBS="$LIBS"
AC_SEARCH_LIBS(pow, [m], , AC_MSG_ERROR([Could not find pow in libm or libc.]))
if test "$ac_cv_search_pow" != "none required"; then
    TOR_LIB_MATH="$ac_cv_search_pow"
fi
LIBS="$save_LIBS"
AC_SUBST(TOR_LIB_MATH)

dnl ------------------------------------------------------
dnl Where do you live, openssl?  And how do we call you?

tor_openssl_pkg_redhat="openssl"
tor_openssl_pkg_debian="libssl-dev"
tor_openssl_devpkg_redhat="openssl-devel"
tor_openssl_devpkg_debian="libssl-dev"

ALT_openssl_WITHVAL=""
AC_ARG_WITH(ssl-dir,
  AS_HELP_STRING(--with-ssl-dir=PATH, [obsolete alias for --with-openssl-dir]),
  [
      if test "x$withval" != "xno" && test "x$withval" != "x"; then
         ALT_openssl_WITHVAL="$withval"
      fi
  ])

AC_MSG_NOTICE([Now, we'll look for OpenSSL >= 1.0.1])
TOR_SEARCH_LIBRARY(openssl, $tryssldir, [-lssl -lcrypto $TOR_LIB_GDI $TOR_LIB_WS32],
    [#include <openssl/ssl.h>],
    [struct ssl_method_st; const struct ssl_method_st *TLSv1_1_method(void);],
    [TLSv1_1_method();], [],
    [/usr/local/opt/openssl /usr/local/openssl /usr/lib/openssl /usr/local/ssl /usr/lib/ssl /usr/local /opt/openssl])

dnl XXXX check for OPENSSL_VERSION_NUMBER == SSLeay()

if test "$enable_static_openssl" = "yes"; then
   if test "$tor_cv_library_openssl_dir" = "(system)"; then
     AC_MSG_ERROR("You must specify an explicit --with-openssl-dir=x option when using --enable-static-openssl")
   else
     TOR_OPENSSL_LIBS="$TOR_LIBDIR_openssl/libssl.a $TOR_LIBDIR_openssl/libcrypto.a"
   fi
else
     TOR_OPENSSL_LIBS="-lssl -lcrypto"
fi
AC_SUBST(TOR_OPENSSL_LIBS)

dnl Now check for particular openssl functions.
save_LIBS="$LIBS"
save_LDFLAGS="$LDFLAGS"
save_CPPFLAGS="$CPPFLAGS"
LIBS="$TOR_OPENSSL_LIBS $LIBS"
LDFLAGS="$TOR_LDFLAGS_openssl $LDFLAGS"
CPPFLAGS="$TOR_CPPFLAGS_openssl $CPPFLAGS"

AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
#include <openssl/opensslv.h>
#if !defined(LIBRESSL_VERSION_NUMBER) && OPENSSL_VERSION_NUMBER < 0x1000100fL
#error "too old"
#endif
   ]], [[]])],
   [ : ],
   [ AC_MSG_ERROR([OpenSSL is too old. We require 1.0.1 or later. You can specify a path to a newer one with --with-openssl-dir.]) ])

AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
#include <openssl/opensslv.h>
#include <openssl/evp.h>
#if defined(OPENSSL_NO_EC) || defined(OPENSSL_NO_ECDH) || defined(OPENSSL_NO_ECDSA)
#error "no ECC"
#endif
#if !defined(NID_X9_62_prime256v1) || !defined(NID_secp224r1)
#error "curves unavailable"
#endif
   ]], [[]])],
   [ : ],
   [ AC_MSG_ERROR([OpenSSL is built without full ECC support, including curves P256 and P224. You can specify a path to one with ECC support with --with-openssl-dir.]) ])

AC_CHECK_MEMBERS([struct ssl_method_st.get_cipher_by_char], , ,
[#include <openssl/ssl.h>
])

AC_CHECK_FUNCS([ \
		SSL_SESSION_get_master_key \
		SSL_get_server_random \
                SSL_get_client_ciphers \
                SSL_get_client_random \
		SSL_CIPHER_find \
		TLS_method
	       ])

dnl Check if OpenSSL has scrypt implementation.
AC_CHECK_FUNCS([ EVP_PBE_scrypt ])

dnl Check if OpenSSL structures are opaque
AC_CHECK_MEMBERS([SSL.state], , ,
[#include <openssl/ssl.h>
])

dnl Define the set of checks for KIST scheduler support.
AC_DEFUN([CHECK_KIST_SUPPORT],[
  dnl KIST needs struct tcp_info and for certain members to exist.
  AC_CHECK_MEMBERS(
    [struct tcp_info.tcpi_unacked, struct tcp_info.tcpi_snd_mss],
    , ,[[#include <netinet/tcp.h>]])
  dnl KIST needs SIOCOUTQNSD to exist for an ioctl call.
  AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [
                     #include <linux/sockios.h>
                     #ifndef SIOCOUTQNSD
                     #error
                     #endif
                     ])], have_siocoutqnsd=yes, have_siocoutqnsd=no)
  if test "x$have_siocoutqnsd" = "xyes"; then
    if test "x$ac_cv_member_struct_tcp_info_tcpi_unacked" = "xyes"; then
      if test "x$ac_cv_member_struct_tcp_info_tcpi_snd_mss" = "xyes"; then
        have_kist_support=yes
      fi
    fi
  fi
])
dnl Now, trigger the check.
CHECK_KIST_SUPPORT
AS_IF([test "x$have_kist_support" = "xyes"],
      [AC_DEFINE(HAVE_KIST_SUPPORT, 1, [Defined if KIST scheduler is supported
                                        on this system])],
      [AC_MSG_NOTICE([KIST scheduler can't be used. Missing support.])])

LIBS="$save_LIBS"
LDFLAGS="$save_LDFLAGS"
CPPFLAGS="$save_CPPFLAGS"

dnl ------------------------------------------------------
dnl Where do you live, zlib?  And how do we call you?

tor_zlib_pkg_redhat="zlib"
tor_zlib_pkg_debian="zlib1g"
tor_zlib_devpkg_redhat="zlib-devel"
tor_zlib_devpkg_debian="zlib1g-dev"

TOR_SEARCH_LIBRARY(zlib, $tryzlibdir, [-lz],
    [#include <zlib.h>],
    [const char * zlibVersion(void);],
    [zlibVersion();], [--with-zlib-dir],
    [/opt/zlib])

if test "$enable_static_zlib" = "yes"; then
   if test "$tor_cv_library_zlib_dir" = "(system)"; then
     AC_MSG_ERROR("You must specify an explicit --with-zlib-dir=x option when
 using --enable-static-zlib")
   else
     TOR_ZLIB_LIBS="$TOR_LIBDIR_zlib/libz.a"
   fi
else
     TOR_ZLIB_LIBS="-lz"
fi
AC_SUBST(TOR_ZLIB_LIBS)

dnl ------------------------------------------------------
dnl Where we do we find lzma?

AC_ARG_ENABLE(lzma,
      AS_HELP_STRING(--enable-lzma, [enable support for the LZMA compression scheme.]),
      [case "${enableval}" in
        "yes") lzma=true ;;
        "no")  lzma=false ;;
        * ) AC_MSG_ERROR(bad value for --enable-lzma) ;;
      esac], [lzma=auto])

if test "x$enable_lzma" = "xno"; then
    have_lzma=no;
else
    PKG_CHECK_MODULES([LZMA],
                      [liblzma],
                      have_lzma=yes,
                      have_lzma=no)

    if test "x$have_lzma" = "xno" ; then
        AC_MSG_WARN([Unable to find liblzma.])
    fi
fi

if test "x$have_lzma" = "xyes"; then
    AC_DEFINE(HAVE_LZMA,1,[Have LZMA])
    TOR_LZMA_CFLAGS="${LZMA_CFLAGS}"
    TOR_LZMA_LIBS="${LZMA_LIBS}"
fi
AC_SUBST(TOR_LZMA_CFLAGS)
AC_SUBST(TOR_LZMA_LIBS)

dnl ------------------------------------------------------
dnl Where we do we find zstd?

AC_ARG_ENABLE(zstd,
      AS_HELP_STRING(--enable-zstd, [enable support for the Zstandard compression scheme.]),
      [case "${enableval}" in
        "yes") zstd=true ;;
        "no")  zstd=false ;;
        * ) AC_MSG_ERROR(bad value for --enable-zstd) ;;
      esac], [zstd=auto])

if test "x$enable_zstd" = "xno"; then
    have_zstd=no;
else
    PKG_CHECK_MODULES([ZSTD],
                      [libzstd >= 1.1],
                      have_zstd=yes,
                      have_zstd=no)

    if test "x$have_zstd" = "xno" ; then
        AC_MSG_WARN([Unable to find libzstd.])
    fi
fi

if test "x$have_zstd" = "xyes"; then
    AC_DEFINE(HAVE_ZSTD,1,[Have Zstd])
    TOR_ZSTD_CFLAGS="${ZSTD_CFLAGS}"
    TOR_ZSTD_LIBS="${ZSTD_LIBS}"
fi
AC_SUBST(TOR_ZSTD_CFLAGS)
AC_SUBST(TOR_ZSTD_LIBS)

dnl ----------------------------------------------------------------------
dnl Check if libcap is available for capabilities.

tor_cap_pkg_debian="libcap2"
tor_cap_pkg_redhat="libcap"
tor_cap_devpkg_debian="libcap-dev"
tor_cap_devpkg_redhat="libcap-devel"

AC_CHECK_LIB([cap], [cap_init], [],
  AC_MSG_NOTICE([Libcap was not found. Capabilities will not be usable.])
)
AC_CHECK_FUNCS(cap_set_proc)

dnl ---------------------------------------------------------------------
dnl Now that we know about our major libraries, we can check for compiler
dnl and linker hardening options.  We need to do this with the libraries known,
dnl since sometimes the linker will like an option but not be willing to
dnl use it with a build of a library.

all_ldflags_for_check="$TOR_LDFLAGS_zlib $TOR_LDFLAGS_openssl $TOR_LDFLAGS_libevent"
all_libs_for_check="$TOR_ZLIB_LIBS $TOR_LIB_MATH $TOR_LIBEVENT_LIBS $TOR_OPENSSL_LIBS $TOR_SYSTEMD_LIBS $TOR_LIB_WS32 $TOR_LIB_GDI $TOR_LIB_USERENV $TOR_CAP_LIBS"

CFLAGS_FTRAPV=
CFLAGS_FWRAPV=
CFLAGS_ASAN=
CFLAGS_UBSAN=


AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [
#if !defined(__clang__)
#error
#endif])], have_clang=yes, have_clang=no)

if test "x$enable_gcc_hardening" != "xno"; then
    CFLAGS="$CFLAGS -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2"
    if test "x$have_clang" = "xyes"; then
        TOR_CHECK_CFLAGS(-Qunused-arguments)
    fi
    TOR_CHECK_CFLAGS(-fstack-protector-all, also_link)
    AS_VAR_PUSHDEF([can_compile], [tor_cv_cflags_-fstack-protector-all])
    AS_VAR_PUSHDEF([can_link], [tor_can_link_-fstack-protector-all])
m4_ifdef([AS_VAR_IF],[
    AS_VAR_IF(can_compile, [yes],
        AS_VAR_IF(can_link, [yes],
                  [],
                  AC_MSG_ERROR([We tried to build with stack protection; it looks like your compiler supports it but your libc does not provide it. Are you missing libssp? (You can --disable-gcc-hardening to ignore this error.)]))
        )])
    AS_VAR_POPDEF([can_link])
    AS_VAR_POPDEF([can_compile])
    TOR_CHECK_CFLAGS(-Wstack-protector)
    TOR_CHECK_CFLAGS(--param ssp-buffer-size=1)
    if test "$bwin32" = "false" && test "$enable_libfuzzer" != "yes" && test "$enable_oss_fuzz" != "yes"; then
       TOR_CHECK_CFLAGS(-fPIE)
       TOR_CHECK_LDFLAGS(-pie, "$all_ldflags_for_check", "$all_libs_for_check")
    fi
    TOR_TRY_COMPILE_WITH_CFLAGS(-fwrapv, also_link, CFLAGS_FWRAPV="-fwrapv", true)
fi

if test "$fragile_hardening" = "yes"; then
    TOR_TRY_COMPILE_WITH_CFLAGS(-ftrapv, also_link, CFLAGS_FTRAPV="-ftrapv", true)
   if test "$tor_cv_cflags__ftrapv" = "yes" && test "$tor_can_link__ftrapv" != "yes"; then
      AC_MSG_WARN([The compiler supports -ftrapv, but for some reason I was not able to link with -ftrapv. Are you missing run-time support? Run-time hardening will not work as well as it should.])
   fi

   if test "$tor_cv_cflags__ftrapv" != "yes"; then
     AC_MSG_ERROR([You requested fragile hardening, but the compiler does not seem to support -ftrapv.])
   fi

   TOR_TRY_COMPILE_WITH_CFLAGS([-fsanitize=address], also_link, CFLAGS_ASAN="-fsanitize=address", true)
    if test "$tor_cv_cflags__fsanitize_address" = "yes" && test "$tor_can_link__fsanitize_address" != "yes"; then
      AC_MSG_ERROR([The compiler supports -fsanitize=address, but for some reason I was not able to link when using it. Are you missing run-time support? With GCC you need libubsan.*, and with Clang you need libclang_rt.ubsan*])
    fi

   TOR_TRY_COMPILE_WITH_CFLAGS([-fsanitize=undefined], also_link, CFLAGS_UBSAN="-fsanitize=undefined", true)
    if test "$tor_cv_cflags__fsanitize_address" = "yes" && test "$tor_can_link__fsanitize_address" != "yes"; then
      AC_MSG_ERROR([The compiler supports -fsanitize=undefined, but for some reason I was not able to link when using it. Are you missing run-time support? With GCC you need libasan.*, and with Clang you need libclang_rt.ubsan*])
    fi

TOR_CHECK_CFLAGS([-fno-omit-frame-pointer])
fi

CFLAGS_BUGTRAP="$CFLAGS_FTRAPV $CFLAGS_ASAN $CFLAGS_UBSAN"
CFLAGS_CONSTTIME="$CFLAGS_FWRAPV"

mulodi_fixes_ftrapv=no
if test "$have_clang" = "yes"; then
  saved_CFLAGS="$CFLAGS"
  CFLAGS="$CFLAGS $CFLAGS_FTRAPV"
  AC_MSG_CHECKING([whether clang -ftrapv can link a 64-bit int multiply])
  AC_LINK_IFELSE([
      AC_LANG_SOURCE([[
          #include <stdint.h>
          #include <stdlib.h>
	  int main(int argc, char **argv)
	  {
            int64_t x = ((int64_t)atoi(argv[1])) * (int64_t)atoi(argv[2])
	                * (int64_t)atoi(argv[3]);
	    return x == 9;
	  } ]])],
	  [ftrapv_can_link=yes; AC_MSG_RESULT([yes])],
	  [ftrapv_can_link=no; AC_MSG_RESULT([no])])
  if test "$ftrapv_can_link" = "no"; then
    AC_MSG_CHECKING([whether defining __mulodi4 fixes that])
    AC_LINK_IFELSE([
      AC_LANG_SOURCE([[
          #include <stdint.h>
          #include <stdlib.h>
	  int64_t __mulodi4(int64_t a, int64_t b, int *overflow) {
             *overflow=0;
	     return a;
          }
	  int main(int argc, char **argv)
	  {
            int64_t x = ((int64_t)atoi(argv[1])) * (int64_t)atoi(argv[2])
	                * (int64_t)atoi(argv[3]);
	    return x == 9;
	  } ]])],
	  [mulodi_fixes_ftrapv=yes; AC_MSG_RESULT([yes])],
	  [mulodi_fixes_ftrapv=no; AC_MSG_RESULT([no])])
  fi
  CFLAGS="$saved_CFLAGS"
fi

AM_CONDITIONAL(ADD_MULODI4, test "$mulodi_fixes_ftrapv" = "yes")

dnl These cflags add bunches of branches, and we haven't been able to
dnl persuade ourselves that they're suitable for code that needs to be
dnl constant time.
AC_SUBST(CFLAGS_BUGTRAP)
dnl These cflags are variant ones sutable for code that needs to be
dnl constant-time.
AC_SUBST(CFLAGS_CONSTTIME)

if test "x$enable_linker_hardening" != "xno"; then
    TOR_CHECK_LDFLAGS(-z relro -z now, "$all_ldflags_for_check", "$all_libs_for_check")
fi

# For backtrace support
TOR_CHECK_LDFLAGS(-rdynamic)

dnl ------------------------------------------------------
dnl Now see if we have a -fomit-frame-pointer compiler option.

saved_CFLAGS="$CFLAGS"
TOR_CHECK_CFLAGS(-fomit-frame-pointer)
F_OMIT_FRAME_POINTER=''
if test "$saved_CFLAGS" != "$CFLAGS"; then
  if test "$fragile_hardening" = "yes"; then
    F_OMIT_FRAME_POINTER='-fomit-frame-pointer'
  fi
fi
CFLAGS="$saved_CFLAGS"
AC_SUBST(F_OMIT_FRAME_POINTER)

dnl ------------------------------------------------------
dnl If we are adding -fomit-frame-pointer (or if the compiler's doing it
dnl for us, as GCC 4.6 and later do at many optimization levels), then
dnl we should try to add -fasynchronous-unwind-tables so that our backtrace
dnl code will work.
TOR_CHECK_CFLAGS(-fasynchronous-unwind-tables)