Issue #6834: replace the implementation for the 'python' and 'pythonw' executables on OSX.

The previous implementation used execv(2) to run the real interpreter, which means that
you cannot use the arch(1) tool to select the architecture you want to use for a
universal build because that only affects the python/pythonw wrapper and not the actual
interpreter.

The new version uses posix_spawnv with a number of OSX-specific options that ensure that
the real interpreter is started using the same CPU architecture as the wrapper, and that
means that 'arch -ppc python' now actually works.

I've also changed the way that the wrapper looks for the framework: it is now linked to
the framework rather than hardcoding the framework path. This should make it easier to
provide pythonw support in tools like virtualenv.

1 files changed, 135 insertions, 5 deletions

diff --git a/Mac/Tools/pythonw.c b/Mac/Tools/pythonw.c
index e70a76f..d7a86f2 100644
--- a/Mac/Tools/pythonw.c
+++ b/Mac/Tools/pythonw.c
@@ -3,15 +3,145 @@
  * application bundle inside the Python framework. This is needed to run
  * GUI code: some GUI API's don't work unless the program is inside an
  * application bundle.
+ *
+ * This program uses posix_spawn rather than plain execv because we need
+ * slightly more control over how the "real" interpreter is executed.
  */
 #include <unistd.h>
+#include <spawn.h>
+#include <stdio.h>
+#include <string.h>
+#include <errno.h>
 #include <err.h>
+#include <dlfcn.h>
+#include <stdlib.h>
+#include <Python.h>
 
-static char Python[] = PYTHONWEXECUTABLE;
 
-int main(int argc, char **argv) {
-	argv[0] = Python;
-	execv(Python, argv);
-	err(1, "execv: %s", Python);
+extern char** environ;
+
+/*
+ * Locate the python framework by looking for the
+ * library that contains Py_Initialize.
+ *
+ * In a regular framework the structure is:
+ *
+ *    Python.framework/Versions/2.7
+ *    		/Python
+ *		/Resources/Python.app/Contents/MacOS/Python
+ *
+ * In a virtualenv style structure the expected
+ * structure is:
+ *
+ *    ROOT
+ *       /bin/pythonw
+ *       /.Python   <- the dylib
+ *       /.Resources/Python.app/Contents/MacOS/Python
+ *
+ * NOTE: virtualenv's are not an officially supported 
+ * feature, support for that structure is provided as
+ * a convenience.
+ */
+static char* get_python_path(void)
+{
+	size_t len;
+	Dl_info info;
+	char* end;
+	char* g_path;
+
+	if (dladdr(Py_Initialize, &info) == 0) {
+		return NULL;
+	}
+
+	len = strlen(info.dli_fname);
+
+	g_path = malloc(len+60);
+	if (g_path == NULL) {
+		return NULL;
+	}
+
+	strcpy(g_path, info.dli_fname);
+	end = g_path + len - 1;
+	while (end != g_path && *end != '/') {
+		end --;
+	}
+	end++;
+	if (end[1] == '.') {
+		end++;
+	}
+	strcpy(end, "Resources/Python.app/Contents/MacOS/Python");
+
+	return g_path;
+}
+
+static void
+setup_spawnattr(posix_spawnattr_t* spawnattr)
+{
+	size_t ocount;
+	size_t count;
+	cpu_type_t cpu_types[1];
+	short flags = 0;
+#ifdef __LP64__
+	int   ch;
+#endif
+
+	if ((errno = posix_spawnattr_init(spawnattr)) != 0) {
+		err(2, "posix_spawnattr_int");
+		/* NOTREACHTED */
+	}
+
+	count = 1;
+
+	/* Run the real python executable using the same architure as this 
+	 * executable, this allows users to controle the architecture using 
+	 * "arch -ppc python"
+	 */
+
+#if defined(__ppc64__)
+	cpu_types[0] = CPU_TYPE_POWERPC64;
+
+#elif defined(__x86_64__)
+	cpu_types[0] = CPU_TYPE_X86_64;
+
+#elif defined(__ppc__)
+	cpu_types[0] = CPU_TYPE_POWERPC;
+#elif defined(__i386__)
+	cpu_types[0] = CPU_TYPE_X86;
+#else
+#	error "Unknown CPU"
+#endif
+
+	if (posix_spawnattr_setbinpref_np(spawnattr, count, 
+				cpu_types, &ocount) == -1) {
+		err(1, "posix_spawnattr_setbinpref");
+		/* NOTREACHTED */
+	}
+	if (count != ocount) {
+		fprintf(stderr, "posix_spawnattr_setbinpref failed to copy\n");
+		exit(1);
+		/* NOTREACHTED */
+	}
+
+
+	/* 
+	 * Set flag that causes posix_spawn to behave like execv
+	 */
+	flags |= POSIX_SPAWN_SETEXEC;
+	if ((errno = posix_spawnattr_setflags(spawnattr, flags)) != 0) {
+		err(1, "posix_spawnattr_setflags");
+		/* NOTREACHTED */
+	}
+}
+
+int 
+main(int argc, char **argv) {
+	posix_spawnattr_t spawnattr = NULL;
+	char* exec_path = get_python_path();
+
+
+	setup_spawnattr(&spawnattr);		
+	posix_spawn(NULL, exec_path, NULL,
+		&spawnattr, argv, environ);
+	err(1, "posix_spawn: %s", argv[0]);
 	/* NOTREACHED */
 }