Fixes Issue #16114: The subprocess module no longer provides a
misleading error message stating that args[0] did not exist when
either the cwd or executable keyword arguments specified a path that
did not exist.
It now keeps track of if the child got as far as preexec and reports it if
not back to the parent via a special "noexec" error message value in
the error pipe so that the cwd can be blamed for a failed chdir
instead of the exec of the executable being blamed instead.
The executable is also always reported accurately when exec fails.
Unittests enhanced to cover these cases.
diff --git a/Modules/_posixsubprocess.c b/Modules/_posixsubprocess.c
index 59673f4..19ca31f 100644
--- a/Modules/_posixsubprocess.c
+++ b/Modules/_posixsubprocess.c
@@ -354,7 +354,7 @@
PyObject *preexec_fn,
PyObject *preexec_fn_args_tuple)
{
- int i, saved_errno, unused;
+ int i, saved_errno, unused, reached_preexec = 0;
PyObject *result;
const char* err_msg = "";
/* Buffer large enough to hold a hex integer. We can't malloc. */
@@ -438,6 +438,7 @@
POSIX_CALL(setsid());
#endif
+ reached_preexec = 1;
if (preexec_fn != Py_None && preexec_fn_args_tuple) {
/* This is where the user has asked us to deadlock their program. */
result = PyObject_Call(preexec_fn, preexec_fn_args_tuple, NULL);
@@ -487,6 +488,10 @@
}
unused = write(errpipe_write, cur, hex_errno + sizeof(hex_errno) - cur);
unused = write(errpipe_write, ":", 1);
+ if (!reached_preexec) {
+ /* Indicate to the parent that the error happened before exec(). */
+ unused = write(errpipe_write, "noexec", 6);
+ }
/* We can't call strerror(saved_errno). It is not async signal safe.
* The parent process will look the error message up. */
} else {