patch@27082 Allow fatal exceptions to bring up VMS debugger

From: "John E. Malmberg" <wb8tyw@qsl.net>
	Message-id: <43E516E0.1000508@qsl.net>

p4raw-id: //depot/perl@27114

2 files changed, 51 insertions, 3 deletions

diff --git a/vms/perlvms.pod b/vms/perlvms.pod
index 78655d245c..8bcb8eb840 100644
--- a/vms/perlvms.pod
+++ b/vms/perlvms.pod
@@ -367,6 +367,30 @@ The PERL5LIB and PERLLIB logical names work as documented in L<perl>,
 except that the element separator is '|' instead of ':'.  The
 directory specifications may use either VMS or Unix syntax.
 
+=head1 PERL_VMS_EXCEPTION_DEBUG
+
+The PERL_VMS_EXCEPTION_DEBUG being defined as "ENABLE" will cause the VMS
+debugger to be invoked if a fatal exception that is not otherwise
+handled is raised.  The purpose of this is to allow debugging of
+internal Perl problems that would cause such a condition.
+
+This allows the programmer to look at the execution stack and variables to
+find out the cause of the exception.  As the debugger is being invoked as
+the Perl interpreter is about to do a fatal exit, continuing the execution
+in debug mode is usally not practical.
+
+Starting Perl in the VMS debugger may change the program execution
+profile in a way that such problems are not reproduced.
+
+The C<kill> function can be used to test this functionality from within
+a program.
+
+In typical VMS style, only the first letter of the value of this logical
+name is actually checked in a case insensitive mode, and it is considered
+enabled if it is the value "T","1" or "E".
+
+This logical name must be defined before Perl is started.
+
 =head1 Command line
 
 =head2 I/O redirection and backgrounding
diff --git a/vms/vms.c b/vms/vms.c
index 14248a6063..d66dd7409c 100644
--- a/vms/vms.c
+++ b/vms/vms.c
@@ -250,6 +250,8 @@ int decc_bug_devnull = 1;
 int decc_bug_fgetname = 0;
 int decc_dir_barename = 0;
 
+static int vms_debug_on_exception = 0;
+
 /* Is this a UNIX file specification?
  *   No longer a simple check with EFS file specs
  *   For now, not a full check, but need to
@@ -1660,8 +1662,8 @@ Perl_my_sigaction (pTHX_ int sig, const struct sigaction* act,
 
 #define _MY_SIG_MAX 17
 
-unsigned int
-Perl_sig_to_vmscondition(int sig)
+static unsigned int
+Perl_sig_to_vmscondition_int(int sig)
 {
     static unsigned int sig_code[_MY_SIG_MAX+1] = 
     {
@@ -1703,6 +1705,17 @@ Perl_sig_to_vmscondition(int sig)
     return sig_code[sig];
 }
 
+unsigned int
+Perl_sig_to_vmscondition(int sig)
+{
+#ifdef SS$_DEBUG
+    if (vms_debug_on_exception != 0)
+	lib$signal(SS$_DEBUG);
+#endif
+    return Perl_sig_to_vmscondition_int(sig);
+}
+
+
 int
 Perl_my_kill(int pid, int sig)
 {
@@ -1738,7 +1751,7 @@ Perl_my_kill(int pid, int sig)
 	return -1;
     }
 
-    code = Perl_sig_to_vmscondition(sig);
+    code = Perl_sig_to_vmscondition_int(sig);
 
     if (!code) {
 	SETERRNO(EINVAL, SS$_BADPARAM);
@@ -10866,6 +10879,17 @@ static int set_features
     unsigned long case_image;
 #endif
 
+    /* Allow an exception to bring Perl into the VMS debugger */
+    vms_debug_on_exception = 0;
+    status = sys_trnlnm("PERL_VMS_EXCEPTION_DEBUG", val_str, sizeof(val_str));
+    if ($VMS_STATUS_SUCCESS(status)) {
+       if ((val_str[0] == 'E') || (val_str[0] == '1') || (val_str[0] == 'T'))
+	 vms_debug_on_exception = 1;
+       else
+	 vms_debug_on_exception = 0;
+    }
+
+
     /* hacks to see if known bugs are still present for testing */
 
     /* Readdir is returning filenames in VMS syntax always */