Where available, use sysctl() with KERN_PROC_PATHNAME to make $^X absolute.

In Configure, check whether sysctl() and KERN_PROC_PATHNAME can be used
to find the absolute pathname of the executable. If so, set
usekernprocpathname in config.sh and USE_KERN_PROC_PATHNAME in config.h.
If this is set, then use this approach in S_set_caret_X() to canonicalise
$^X as an absolute path. This approach works on (at least) FreeBSD, and
doesn't rely on the /proc filesystem existing, or /proc/curproc/file being
present.

1 files changed, 117 insertions, 0 deletions

diff --git a/Configure b/Configure
index 42a0a19ee8..691bd81964 100755
--- a/Configure
+++ b/Configure
@@ -1234,6 +1234,7 @@ usesocks=''
 d_oldpthreads=''
 use5005threads=''
 useithreads=''
+usekernprocpathname=''
 usereentrant=''
 usethreads=''
 incpath=''
@@ -19346,6 +19347,121 @@ $rm_try
 set ebcdic
 eval $setvar
 
+: Determine if we can use sysctl with KERN_PROC_PATHNAME to find executing program
+echo " "
+echo "Determining whether we can use sysctl with KERN_PROC_PATHNAME to find executing program..." >&4
+$cat >try.c <<'EOM'
+/* Intentionally a long probe as I'd like to sanity check that the exact
+   approach is going to work, as thinking it will work, but only having it
+   part working at runtime is worse than not having it.  */
+
+#include <sys/types.h>
+#include <sys/sysctl.h>
+#include <sys/param.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+int
+main(int argc, char **argv) {
+    char *buffer;
+    char *argv_leaf = strrchr(argv[0], '/');
+    char *buffer_leaf;
+    size_t size = 0;
+    int mib[4];
+
+    mib[0] = CTL_KERN;
+    mib[1] = KERN_PROC;
+    mib[2] = KERN_PROC_PATHNAME;
+    mib[3] = -1;
+
+    if (!argv_leaf) {
+	fprintf(stderr, "Can't locate / in '%s'\n", argv[0]);
+	return 1;
+    }
+
+    if (sysctl(mib, 4, NULL, &size, NULL, 0)) {
+	perror("sysctl");
+	return 2;
+    }
+
+    if (size < strlen(argv_leaf) + 1) {
+	fprintf(stderr, "size %lu is too short for a path\n",
+		(unsigned long) size);
+	return 3;
+    }
+
+    if (size > MAXPATHLEN * MAXPATHLEN) {
+	fprintf(stderr, "size %lu is too long for a path\n",
+		(unsigned long) size);
+	return 4;
+    }
+
+    buffer = malloc(size);
+    if (!buffer) {
+	perror("malloc");
+	return 5;
+    }
+
+    if (sysctl(mib, 4, buffer, &size, NULL, 0)) {
+	perror("sysctl");
+	return 6;
+    }
+
+    if (strlen(buffer) + 1 != size) {
+	fprintf(stderr, "size != strlen(buffer) + 1 (%lu != %lu)\n",
+		(unsigned long)size, (unsigned long)strlen(buffer) + 1);
+        return 7;
+    }
+
+
+    if (*buffer != '/') {
+	fprintf(stderr, "Not an absolute path: '%s'\n", buffer);
+	return 8;
+    }
+
+    if (strstr(buffer, "/./")) {
+	fprintf(stderr, "Contains /./: '%s'\n", buffer);
+	return 9;
+    }
+
+    if (strstr(buffer, "/../")) {
+	fprintf(stderr, "Contains /../: '%s'\n", buffer);
+	return 10;
+    }
+
+    buffer_leaf = strrchr(buffer, '/');
+    if (strcmp(buffer_leaf, argv_leaf) != 0) {
+	fprintf(stderr, "Leafnames differ: '%s' vs '%s'\n", argv[0], buffer);
+	return 11;
+    }
+
+    free(buffer);
+
+    return 0;
+}
+EOM
+
+val=$undef
+set try
+if eval $compile_ok; then
+	if $run ./try; then
+		echo "You can use sysctl with KERN_PROC_PATHNAME to find the executing program." >&4
+		val="$define"
+	else
+		echo "Nope, sysctl with KERN_PROC_PATHNAME doesn't work here." >&4
+		val="$undef"
+	fi
+else
+	echo "I'm unable to compile the test program." >&4
+	echo "I'll assume no sysctl with KERN_PROC_PATHNAME here." >&4
+	val="$undef"
+fi
+$rm_try
+set usekernprocpathname
+eval $setvar
+
 : Check how to flush
 echo " "
 $cat >&4 <<EOM
@@ -23434,6 +23550,7 @@ usedl='$usedl'
 usedtrace='$usedtrace'
 usefaststdio='$usefaststdio'
 useithreads='$useithreads'
+usekernprocpathname='$usekernprocpathname'
 uselargefiles='$uselargefiles'
 uselongdouble='$uselongdouble'
 usemallocwrap='$usemallocwrap'