Try filling CFProcessPath with argv[0] on OpenBSD.

There is no native mechanism to get the running process path on OpenBSD.
Currently, the shell needs to cooperate and fill in the path. This
works, but not all shells set the `_` environment variable.

We however are able to get `argv[0]` via sysctl on this platform.
Instead of just trying `_` and then giving up otherwise, first try
getting `argv[0]`. If that appears to be an absolute path, then we can
likely assume that this is what we need; otherwise, search PATH.

On other BSD platforms, this sysctl may need to be modified or an
alternative mechanism supplied to get `argv[0]`, so we still fallback on
`getenv("_")`.

Author: 3405691582

CoreFoundation/Base.subproj/CFPlatform.c

@@ -119,6 +119,12 @@ static inline void _CFSetProgramNameFromPath(const char *path) {
     __CFprogname = (__CFprogname ? __CFprogname + 1 : __CFProcessPath);
 }
 
+#if TARGET_OS_BSD && defined(__OpenBSD__)
+#include <sys/types.h>
+#include <sys/sysctl.h>
+#include <sys/exec.h>
+#endif
+
 const char *_CFProcessPath(void) {
     if (__CFProcessPath) return __CFProcessPath;
 
@@ -175,6 +181,50 @@ const char *_CFProcessPath(void) {
     }
     return __CFProcessPath;
 #else // TARGET_OS_BSD
+    char *argv0 = NULL;
+
+    // Get argv[0].
+#if defined(__OpenBSD__)
+    int mib[2] = {CTL_VM, VM_PSSTRINGS};
+    struct _ps_strings _ps;
+    size_t len = sizeof(_ps);
+
+    if (sysctl(mib, 2, &_ps, &len, NULL, 0) != -1) {
+        struct ps_strings *ps = _ps.val;
+        char *res = realpath(ps->ps_argvstr[0], NULL);
+        argv0 = res? res: strdup(ps->ps_argvstr[0]);
+    }
+#endif
+
+    if (!__CFProcessIsRestricted() && argv0 && argv0[0] == '/') {
+        _CFSetProgramNameFromPath(argv0);
+        free(argv0);
+        return __CFProcessPath;
+    }
+
+    // Search PATH.
+    if (argv0) {
+      char *paths = getenv("PATH");
+      char *p = NULL;
+      while ((p = strsep(&paths, ":")) != NULL) {
+         char pp[PATH_MAX];
+         snprintf(pp, PATH_MAX, "%s/%s", p, argv0);
+         char *res = realpath(pp, NULL);
+         if (!res) {
+             continue;
+         }
+         if (!__CFProcessIsRestricted() && access(res, X_OK) == 0) {
+             _CFSetProgramNameFromPath(res);
+             free(argv0);
+             free(res);
+             return __CFProcessPath;
+         }
+	 free(res);
+      }
+      free(argv0);
+    }
+
+    // See if the shell will help.
     if (!__CFProcessIsRestricted()) {
         char *path = getenv("_");
         if (path != NULL) {