From 65a796e5272f61b42792d3a8c69686558c1872c5 Mon Sep 17 00:00:00 2001 From: Victor Stinner Date: Wed, 1 Apr 2020 18:49:29 +0200 Subject: [PATCH] bpo-40094: Add os.waitstatus_to_exitcode() (GH-19201) Add os.waitstatus_to_exitcode() function to convert a wait status to an exitcode. Suggest waitstatus_to_exitcode() usage in the documentation when appropriate. Use waitstatus_to_exitcode() in: * multiprocessing, os, subprocess and _bootsubprocess modules; * test.support.wait_process(); * setup.py: run_command(); * and many tests. --- Doc/library/os.rst | 56 +++++++++++++ Doc/library/pty.rst | 5 ++ Doc/whatsnew/3.9.rst | 4 + Lib/_bootsubprocess.py | 13 +-- Lib/multiprocessing/forkserver.py | 10 +-- Lib/multiprocessing/popen_fork.py | 6 +- Lib/os.py | 8 +- Lib/subprocess.py | 18 ++--- Lib/test/support/__init__.py | 9 +-- Lib/test/test_os.py | 29 +++++++ Lib/test/test_popen.py | 5 +- Lib/test/test_pty.py | 4 +- Lib/test/test_wait3.py | 3 +- Lib/test/test_wait4.py | 3 +- .../2020-03-28-18-25-49.bpo-40094.v-wQIU.rst | 2 + Modules/clinic/posixmodule.c.h | 62 ++++++++++++++- Modules/posixmodule.c | 79 +++++++++++++++++++ setup.py | 3 +- 18 files changed, 258 insertions(+), 61 deletions(-) create mode 100644 Misc/NEWS.d/next/Library/2020-03-28-18-25-49.bpo-40094.v-wQIU.rst diff --git a/Doc/library/os.rst b/Doc/library/os.rst index 4adca057ed2..f27cf3dbeaf 100644 --- a/Doc/library/os.rst +++ b/Doc/library/os.rst @@ -3665,6 +3665,11 @@ written in Python, such as a mail server's external command delivery program. subprocess was killed.) On Windows systems, the return value contains the signed integer return code from the child process. + On Unix, :func:`waitstatus_to_exitcode` can be used to convert the ``close`` + method result (exit status) into an exit code if it is not ``None``. On + Windows, the ``close`` method result is directly the exit code + (or ``None``). + This is implemented using :class:`subprocess.Popen`; see that class's documentation for more powerful ways to manage and communicate with subprocesses. @@ -3968,6 +3973,10 @@ written in Python, such as a mail server's external command delivery program. to using this function. See the :ref:`subprocess-replacements` section in the :mod:`subprocess` documentation for some helpful recipes. + On Unix, :func:`waitstatus_to_exitcode` can be used to convert the result + (exit status) into an exit code. On Windows, the result is directly the exit + code. + .. audit-event:: os.system command os.system .. availability:: Unix, Windows. @@ -4008,8 +4017,16 @@ written in Python, such as a mail server's external command delivery program. number is zero); the high bit of the low byte is set if a core file was produced. + :func:`waitstatus_to_exitcode` can be used to convert the exit status into an + exit code. + .. availability:: Unix. + .. seealso:: + + :func:`waitpid` can be used to wait for the completion of a specific + child process and has more options. + .. function:: waitid(idtype, id, options) Wait for the completion of one or more child processes. @@ -4105,6 +4122,9 @@ written in Python, such as a mail server's external command delivery program. id is known, not necessarily a child process. The :func:`spawn\* ` functions called with :const:`P_NOWAIT` return suitable process handles. + :func:`waitstatus_to_exitcode` can be used to convert the exit status into an + exit code. + .. versionchanged:: 3.5 If the system call is interrupted and the signal handler does not raise an exception, the function now retries the system call instead of raising an @@ -4120,6 +4140,9 @@ written in Python, such as a mail server's external command delivery program. information. The option argument is the same as that provided to :func:`waitpid` and :func:`wait4`. + :func:`waitstatus_to_exitcode` can be used to convert the exit status into an + exitcode. + .. availability:: Unix. @@ -4131,9 +4154,42 @@ written in Python, such as a mail server's external command delivery program. resource usage information. The arguments to :func:`wait4` are the same as those provided to :func:`waitpid`. + :func:`waitstatus_to_exitcode` can be used to convert the exit status into an + exitcode. + .. availability:: Unix. +.. function:: waitstatus_to_exitcode(status) + + Convert a wait status to an exit code. + + On Unix: + + * If the process exited normally (if ``WIFEXITED(status)`` is true), + return the process exit status (return ``WEXITSTATUS(status)``): + result greater than or equal to 0. + * If the process was terminated by a signal (if ``WIFSIGNALED(status)`` is + true), return ``-signum`` where *signum* is the number of the signal that + caused the process to terminate (return ``-WTERMSIG(status)``): + result less than 0. + * Otherwise, raise a :exc:`ValueError`. + + On Windows, return *status* shifted right by 8 bits. + + On Unix, if the process is being traced or if :func:`waitpid` was called + with :data:`WUNTRACED` option, the caller must first check if + ``WIFSTOPPED(status)`` is true. This function must not be called if + ``WIFSTOPPED(status)`` is true. + + .. seealso:: + + :func:`WIFEXITED`, :func:`WEXITSTATUS`, :func:`WIFSIGNALED`, + :func:`WTERMSIG`, :func:`WIFSTOPPED`, :func:`WSTOPSIG` functions. + + .. versionadded:: 3.9 + + .. data:: WNOHANG The option for :func:`waitpid` to return immediately if no child process status diff --git a/Doc/library/pty.rst b/Doc/library/pty.rst index e85d2e239fd..73d4f102fd4 100644 --- a/Doc/library/pty.rst +++ b/Doc/library/pty.rst @@ -69,6 +69,11 @@ The :mod:`pty` module defines the following functions: *select* throws an error on your platform when passed three empty lists. This is a bug, documented in `issue 26228 `_. + Return the exit status value from :func:`os.waitpid` on the child process. + + :func:`waitstatus_to_exitcode` can be used to convert the exit status into + an exit code. + .. audit-event:: pty.spawn argv pty.spawn .. versionchanged:: 3.4 diff --git a/Doc/whatsnew/3.9.rst b/Doc/whatsnew/3.9.rst index 6ea4ad89f8c..fc48cd67edc 100644 --- a/Doc/whatsnew/3.9.rst +++ b/Doc/whatsnew/3.9.rst @@ -322,6 +322,10 @@ The :func:`os.putenv` and :func:`os.unsetenv` functions are now always available. (Contributed by Victor Stinner in :issue:`39395`.) +Add :func:`os.waitstatus_to_exitcode` function: +convert a wait status to an exit code. +(Contributed by Victor Stinner in :issue:`40094`.) + pathlib ------- diff --git a/Lib/_bootsubprocess.py b/Lib/_bootsubprocess.py index 9c1912f315d..014782f616c 100644 --- a/Lib/_bootsubprocess.py +++ b/Lib/_bootsubprocess.py @@ -6,15 +6,6 @@ subprocess is unavailable. setup.py is not used on Windows. import os -def _waitstatus_to_exitcode(status): - if os.WIFEXITED(status): - return os.WEXITSTATUS(status) - elif os.WIFSIGNALED(status): - return -os.WTERMSIG(status) - else: - raise ValueError(f"invalid wait status: {status!r}") - - # distutils.spawn used by distutils.command.build_ext # calls subprocess.Popen().wait() class Popen: @@ -37,7 +28,7 @@ class Popen: else: # Parent process _, status = os.waitpid(pid, 0) - self.returncode = _waitstatus_to_exitcode(status) + self.returncode = os.waitstatus_to_exitcode(status) return self.returncode @@ -87,7 +78,7 @@ def check_output(cmd, **kwargs): try: # system() spawns a shell status = os.system(cmd) - exitcode = _waitstatus_to_exitcode(status) + exitcode = os.waitstatus_to_exitcode(status) if exitcode: raise ValueError(f"Command {cmd!r} returned non-zero " f"exit status {exitcode!r}") diff --git a/Lib/multiprocessing/forkserver.py b/Lib/multiprocessing/forkserver.py index 215ac39afca..22a911a7a29 100644 --- a/Lib/multiprocessing/forkserver.py +++ b/Lib/multiprocessing/forkserver.py @@ -237,14 +237,8 @@ def main(listener_fd, alive_r, preload, main_path=None, sys_path=None): break child_w = pid_to_fd.pop(pid, None) if child_w is not None: - if os.WIFSIGNALED(sts): - returncode = -os.WTERMSIG(sts) - else: - if not os.WIFEXITED(sts): - raise AssertionError( - "Child {0:n} status is {1:n}".format( - pid,sts)) - returncode = os.WEXITSTATUS(sts) + returncode = os.waitstatus_to_exitcode(sts) + # Send exit code to client process try: write_signed(child_w, returncode) diff --git a/Lib/multiprocessing/popen_fork.py b/Lib/multiprocessing/popen_fork.py index a65b06f1b2c..625981cf476 100644 --- a/Lib/multiprocessing/popen_fork.py +++ b/Lib/multiprocessing/popen_fork.py @@ -30,11 +30,7 @@ class Popen(object): # e.errno == errno.ECHILD == 10 return None if pid == self.pid: - if os.WIFSIGNALED(sts): - self.returncode = -os.WTERMSIG(sts) - else: - assert os.WIFEXITED(sts), "Status is {:n}".format(sts) - self.returncode = os.WEXITSTATUS(sts) + self.returncode = os.waitstatus_to_exitcode(sts) return self.returncode def wait(self, timeout=None): diff --git a/Lib/os.py b/Lib/os.py index 8459baa2e4d..8acd6f12c3e 100644 --- a/Lib/os.py +++ b/Lib/os.py @@ -864,12 +864,8 @@ if _exists("fork") and not _exists("spawnv") and _exists("execv"): wpid, sts = waitpid(pid, 0) if WIFSTOPPED(sts): continue - elif WIFSIGNALED(sts): - return -WTERMSIG(sts) - elif WIFEXITED(sts): - return WEXITSTATUS(sts) - else: - raise OSError("Not stopped, signaled or exited???") + + return waitstatus_to_exitcode(sts) def spawnv(mode, file, args): """spawnv(mode, file, args) -> integer diff --git a/Lib/subprocess.py b/Lib/subprocess.py index c8db387091b..1eecceaed41 100644 --- a/Lib/subprocess.py +++ b/Lib/subprocess.py @@ -1838,23 +1838,17 @@ class Popen(object): raise child_exception_type(err_msg) - def _handle_exitstatus(self, sts, _WIFSIGNALED=os.WIFSIGNALED, - _WTERMSIG=os.WTERMSIG, _WIFEXITED=os.WIFEXITED, - _WEXITSTATUS=os.WEXITSTATUS, _WIFSTOPPED=os.WIFSTOPPED, - _WSTOPSIG=os.WSTOPSIG): + def _handle_exitstatus(self, sts, + waitstatus_to_exitcode=os.waitstatus_to_exitcode, + _WIFSTOPPED=os.WIFSTOPPED, + _WSTOPSIG=os.WSTOPSIG): """All callers to this function MUST hold self._waitpid_lock.""" # This method is called (indirectly) by __del__, so it cannot # refer to anything outside of its local scope. - if _WIFSIGNALED(sts): - self.returncode = -_WTERMSIG(sts) - elif _WIFEXITED(sts): - self.returncode = _WEXITSTATUS(sts) - elif _WIFSTOPPED(sts): + if _WIFSTOPPED(sts): self.returncode = -_WSTOPSIG(sts) else: - # Should never happen - raise SubprocessError("Unknown child exit status!") - + self.returncode = waitstatus_to_exitcode(sts) def _internal_poll(self, _deadstate=None, _waitpid=os.waitpid, _WNOHANG=os.WNOHANG, _ECHILD=errno.ECHILD): diff --git a/Lib/test/support/__init__.py b/Lib/test/support/__init__.py index 7272d475ceb..1f792d8514d 100644 --- a/Lib/test/support/__init__.py +++ b/Lib/test/support/__init__.py @@ -3442,18 +3442,11 @@ def wait_process(pid, *, exitcode, timeout=None): sleep = min(sleep * 2, max_sleep) time.sleep(sleep) - - if os.WIFEXITED(status): - exitcode2 = os.WEXITSTATUS(status) - elif os.WIFSIGNALED(status): - exitcode2 = -os.WTERMSIG(status) - else: - raise ValueError(f"invalid wait status: {status!r}") else: # Windows implementation pid2, status = os.waitpid(pid, 0) - exitcode2 = (status >> 8) + exitcode2 = os.waitstatus_to_exitcode(status) if exitcode2 != exitcode: raise AssertionError(f"process {pid} exited with code {exitcode2}, " f"but exit code {exitcode} is expected") diff --git a/Lib/test/test_os.py b/Lib/test/test_os.py index be85616ff88..142cfea364e 100644 --- a/Lib/test/test_os.py +++ b/Lib/test/test_os.py @@ -2794,6 +2794,35 @@ class PidTests(unittest.TestCase): pid = os.spawnv(os.P_NOWAIT, FakePath(args[0]), args) support.wait_process(pid, exitcode=0) + def test_waitstatus_to_exitcode(self): + exitcode = 23 + filename = support.TESTFN + self.addCleanup(support.unlink, filename) + + with open(filename, "w") as fp: + print(f'import sys; sys.exit({exitcode})', file=fp) + fp.flush() + args = [sys.executable, filename] + pid = os.spawnv(os.P_NOWAIT, args[0], args) + + pid2, status = os.waitpid(pid, 0) + self.assertEqual(os.waitstatus_to_exitcode(status), exitcode) + self.assertEqual(pid2, pid) + + # Skip the test on Windows + @unittest.skipUnless(hasattr(signal, 'SIGKILL'), 'need signal.SIGKILL') + def test_waitstatus_to_exitcode_kill(self): + signum = signal.SIGKILL + args = [sys.executable, '-c', + f'import time; time.sleep({support.LONG_TIMEOUT})'] + pid = os.spawnv(os.P_NOWAIT, args[0], args) + + os.kill(pid, signum) + + pid2, status = os.waitpid(pid, 0) + self.assertEqual(os.waitstatus_to_exitcode(status), -signum) + self.assertEqual(pid2, pid) + class SpawnTests(unittest.TestCase): def create_args(self, *, with_env=False, use_bytes=False): diff --git a/Lib/test/test_popen.py b/Lib/test/test_popen.py index da01a878fa0..ab1bc776552 100644 --- a/Lib/test/test_popen.py +++ b/Lib/test/test_popen.py @@ -44,10 +44,11 @@ class PopenTest(unittest.TestCase): def test_return_code(self): self.assertEqual(os.popen("exit 0").close(), None) + status = os.popen("exit 42").close() if os.name == 'nt': - self.assertEqual(os.popen("exit 42").close(), 42) + self.assertEqual(status, 42) else: - self.assertEqual(os.popen("exit 42").close(), 42 << 8) + self.assertEqual(os.waitstatus_to_exitcode(status), 42) def test_contextmanager(self): with os.popen("echo hello") as f: diff --git a/Lib/test/test_pty.py b/Lib/test/test_pty.py index ce85f575a08..aa5c68790f7 100644 --- a/Lib/test/test_pty.py +++ b/Lib/test/test_pty.py @@ -200,8 +200,8 @@ class PtyTest(unittest.TestCase): ## raise TestFailed("Unexpected output from child: %r" % line) (pid, status) = os.waitpid(pid, 0) - res = status >> 8 - debug("Child (%d) exited with status %d (%d)." % (pid, res, status)) + res = os.waitstatus_to_exitcode(status) + debug("Child (%d) exited with code %d (status %d)." % (pid, res, status)) if res == 1: self.fail("Child raised an unexpected exception in os.setsid()") elif res == 2: diff --git a/Lib/test/test_wait3.py b/Lib/test/test_wait3.py index 6e06049fbdd..aa166baa400 100644 --- a/Lib/test/test_wait3.py +++ b/Lib/test/test_wait3.py @@ -30,8 +30,7 @@ class Wait3Test(ForkWait): time.sleep(0.1) self.assertEqual(spid, cpid) - self.assertEqual(status, exitcode << 8, - "cause = %d, exit = %d" % (status&0xff, status>>8)) + self.assertEqual(os.waitstatus_to_exitcode(status), exitcode) self.assertTrue(rusage) def test_wait3_rusage_initialized(self): diff --git a/Lib/test/test_wait4.py b/Lib/test/test_wait4.py index 6c7ebcb3dd2..f8d5e13014f 100644 --- a/Lib/test/test_wait4.py +++ b/Lib/test/test_wait4.py @@ -29,8 +29,7 @@ class Wait4Test(ForkWait): break time.sleep(0.1) self.assertEqual(spid, cpid) - self.assertEqual(status, exitcode << 8, - "cause = %d, exit = %d" % (status&0xff, status>>8)) + self.assertEqual(os.waitstatus_to_exitcode(status), exitcode) self.assertTrue(rusage) def tearDownModule(): diff --git a/Misc/NEWS.d/next/Library/2020-03-28-18-25-49.bpo-40094.v-wQIU.rst b/Misc/NEWS.d/next/Library/2020-03-28-18-25-49.bpo-40094.v-wQIU.rst new file mode 100644 index 00000000000..b50816f1a9a --- /dev/null +++ b/Misc/NEWS.d/next/Library/2020-03-28-18-25-49.bpo-40094.v-wQIU.rst @@ -0,0 +1,2 @@ +Add :func:`os.waitstatus_to_exitcode` function: +convert a wait status to an exit code. diff --git a/Modules/clinic/posixmodule.c.h b/Modules/clinic/posixmodule.c.h index 48dd7a74b3b..8ff06feb12e 100644 --- a/Modules/clinic/posixmodule.c.h +++ b/Modules/clinic/posixmodule.c.h @@ -8274,6 +8274,62 @@ exit: #endif /* defined(MS_WINDOWS) */ +#if (defined(WIFEXITED) || defined(MS_WINDOWS)) + +PyDoc_STRVAR(os_waitstatus_to_exitcode__doc__, +"waitstatus_to_exitcode($module, /, status)\n" +"--\n" +"\n" +"Convert a wait status to an exit code.\n" +"\n" +"On Unix:\n" +"\n" +"* If WIFEXITED(status) is true, return WEXITSTATUS(status).\n" +"* If WIFSIGNALED(status) is true, return -WTERMSIG(status).\n" +"* Otherwise, raise a ValueError.\n" +"\n" +"On Windows, return status shifted right by 8 bits.\n" +"\n" +"On Unix, if the process is being traced or if waitpid() was called with\n" +"WUNTRACED option, the caller must first check if WIFSTOPPED(status) is true.\n" +"This function must not be called if WIFSTOPPED(status) is true."); + +#define OS_WAITSTATUS_TO_EXITCODE_METHODDEF \ + {"waitstatus_to_exitcode", (PyCFunction)(void(*)(void))os_waitstatus_to_exitcode, METH_FASTCALL|METH_KEYWORDS, os_waitstatus_to_exitcode__doc__}, + +static PyObject * +os_waitstatus_to_exitcode_impl(PyObject *module, int status); + +static PyObject * +os_waitstatus_to_exitcode(PyObject *module, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames) +{ + PyObject *return_value = NULL; + static const char * const _keywords[] = {"status", NULL}; + static _PyArg_Parser _parser = {NULL, _keywords, "waitstatus_to_exitcode", 0}; + PyObject *argsbuf[1]; + int status; + + args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 1, 1, 0, argsbuf); + if (!args) { + goto exit; + } + if (PyFloat_Check(args[0])) { + PyErr_SetString(PyExc_TypeError, + "integer argument expected, got float" ); + goto exit; + } + status = _PyLong_AsInt(args[0]); + if (status == -1 && PyErr_Occurred()) { + goto exit; + } + return_value = os_waitstatus_to_exitcode_impl(module, status); + +exit: + return return_value; +} + +#endif /* (defined(WIFEXITED) || defined(MS_WINDOWS)) */ + #ifndef OS_TTYNAME_METHODDEF #define OS_TTYNAME_METHODDEF #endif /* !defined(OS_TTYNAME_METHODDEF) */ @@ -8809,4 +8865,8 @@ exit: #ifndef OS__REMOVE_DLL_DIRECTORY_METHODDEF #define OS__REMOVE_DLL_DIRECTORY_METHODDEF #endif /* !defined(OS__REMOVE_DLL_DIRECTORY_METHODDEF) */ -/*[clinic end generated code: output=5d99f90cead7c0e1 input=a9049054013a1b77]*/ + +#ifndef OS_WAITSTATUS_TO_EXITCODE_METHODDEF + #define OS_WAITSTATUS_TO_EXITCODE_METHODDEF +#endif /* !defined(OS_WAITSTATUS_TO_EXITCODE_METHODDEF) */ +/*[clinic end generated code: output=4e28994a729eddf9 input=a9049054013a1b77]*/ diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c index 9ab136b2525..1adca8ec29d 100644 --- a/Modules/posixmodule.c +++ b/Modules/posixmodule.c @@ -13771,6 +13771,84 @@ os__remove_dll_directory_impl(PyObject *module, PyObject *cookie) #endif + +/* Only check if WIFEXITED is available: expect that it comes + with WEXITSTATUS, WIFSIGNALED, etc. + + os.waitstatus_to_exitcode() is implemented in C and not in Python, so + subprocess can safely call it during late Python finalization without + risking that used os attributes were set to None by _PyImport_Cleanup(). */ +#if defined(WIFEXITED) || defined(MS_WINDOWS) +/*[clinic input] +os.waitstatus_to_exitcode + + status: int + +Convert a wait status to an exit code. + +On Unix: + +* If WIFEXITED(status) is true, return WEXITSTATUS(status). +* If WIFSIGNALED(status) is true, return -WTERMSIG(status). +* Otherwise, raise a ValueError. + +On Windows, return status shifted right by 8 bits. + +On Unix, if the process is being traced or if waitpid() was called with +WUNTRACED option, the caller must first check if WIFSTOPPED(status) is true. +This function must not be called if WIFSTOPPED(status) is true. +[clinic start generated code]*/ + +static PyObject * +os_waitstatus_to_exitcode_impl(PyObject *module, int status) +/*[clinic end generated code: output=c7c2265731f79b7a input=edfa5ca5006276fb]*/ +{ +#ifndef MS_WINDOWS + WAIT_TYPE wait_status; + WAIT_STATUS_INT(wait_status) = status; + int exitcode; + if (WIFEXITED(wait_status)) { + exitcode = WEXITSTATUS(wait_status); + /* Sanity check to provide warranty on the function behavior. + It should not occur in practice */ + if (exitcode < 0) { + PyErr_Format(PyExc_ValueError, "invalid WEXITSTATUS: %i", exitcode); + return NULL; + } + } + else if (WIFSIGNALED(wait_status)) { + int signum = WTERMSIG(wait_status); + /* Sanity check to provide warranty on the function behavior. + It should not occurs in practice */ + if (signum <= 0) { + PyErr_Format(PyExc_ValueError, "invalid WTERMSIG: %i", signum); + return NULL; + } + exitcode = -signum; + } else if (WIFSTOPPED(wait_status)) { + /* Status only received if the process is being traced + or if waitpid() was called with WUNTRACED option. */ + int signum = WSTOPSIG(wait_status); + PyErr_Format(PyExc_ValueError, + "process stopped by delivery of signal %i", + signum); + return NULL; + } + else { + PyErr_Format(PyExc_ValueError, "invalid wait status: %i", status); + return NULL; + } + return PyLong_FromLong(exitcode); +#else + /* Windows implementation: see os.waitpid() implementation + which uses _cwait(). */ + int exitcode = (status >> 8); + return PyLong_FromLong(exitcode); +#endif +} +#endif + + static PyMethodDef posix_methods[] = { OS_STAT_METHODDEF @@ -13964,6 +14042,7 @@ static PyMethodDef posix_methods[] = { OS__ADD_DLL_DIRECTORY_METHODDEF OS__REMOVE_DLL_DIRECTORY_METHODDEF #endif + OS_WAITSTATUS_TO_EXITCODE_METHODDEF {NULL, NULL} /* Sentinel */ }; diff --git a/setup.py b/setup.py index 3d3e5ac7db0..0357a0124f8 100644 --- a/setup.py +++ b/setup.py @@ -9,7 +9,6 @@ import re import sys import sysconfig from glob import glob -from _bootsubprocess import _waitstatus_to_exitcode as waitstatus_to_exitcode try: @@ -98,7 +97,7 @@ Topic :: Software Development def run_command(cmd): status = os.system(cmd) - return waitstatus_to_exitcode(status) + return os.waitstatus_to_exitcode(status) # Set common compiler and linker flags derived from the Makefile,