Avoid zero-length allocations, which return NULL on z/OS (#810)

It's totally legal to return NULL for malloc(0), but every other
platform that we target returns a non-NULL pointer. We don't need
to do an allocation anyway (nor do we need to copy the terminating
NUL byte).

Author: NWilson

src/pcre2_dfa_match.c

@@ -3342,7 +3342,6 @@ pcre2_dfa_match(const pcre2_code *code, PCRE2_SPTR subject, PCRE2_SIZE length,
   pcre2_match_context *mcontext, int *workspace, PCRE2_SIZE wscount)
 {
 int rc;
-int was_zero_terminated = 0;
 
 const pcre2_real_code *re = (const pcre2_real_code *)code;
 uint32_t original_options = options;
@@ -3403,7 +3402,6 @@ if ((options & ~PUBLIC_DFA_MATCH_OPTIONS) != 0)
 if (length == PCRE2_ZERO_TERMINATED)
   {
   length = PRIV(strlen)(subject);
-  was_zero_terminated = 1;
   }
 
 if (wscount < 20) { rc = PCRE2_ERROR_DFA_WSSIZE; goto EXIT; }
@@ -4062,11 +4060,16 @@ for (;;)
 
     if (rc >= 0 && (options & PCRE2_COPY_MATCHED_SUBJECT) != 0)
       {
-      length = CU2BYTES(length + was_zero_terminated);
-      match_data->subject = match_data->memctl.malloc(length,
-        match_data->memctl.memory_data);
-      if (match_data->subject == NULL) { rc = PCRE2_ERROR_NOMEMORY; goto EXIT; }
-      memcpy((void *)match_data->subject, subject, length);
+      if (length != 0)
+        {
+        match_data->subject = match_data->memctl.malloc(CU2BYTES(length),
+          match_data->memctl.memory_data);
+        if (match_data->subject == NULL)
+          { rc = PCRE2_ERROR_NOMEMORY; goto EXIT; }
+        memcpy((void *)match_data->subject, subject, CU2BYTES(length));
+        }
+      else
+        match_data->subject = NULL;
       match_data->flags |= PCRE2_MD_COPIED_SUBJECT;
       }
     else if (rc >= 0 || rc == PCRE2_ERROR_PARTIAL)

src/pcre2_match.c

@@ -6948,7 +6948,6 @@ pcre2_match(const pcre2_code *code, PCRE2_SPTR subject, PCRE2_SIZE length,
   pcre2_match_context *mcontext)
 {
 int rc;
-int was_zero_terminated = 0;
 const uint8_t *start_bits = NULL;
 const pcre2_real_code *re = (const pcre2_real_code *)code;
 uint32_t original_options = options;
@@ -7024,7 +7023,6 @@ req_cu_ptr = start_match - 1;
 if (length == PCRE2_ZERO_TERMINATED)
   {
   length = PRIV(strlen)(subject);
-  was_zero_terminated = 1;
   }
 true_end_subject = end_subject = subject + length;
 
@@ -7193,12 +7191,16 @@ if (use_jit)
     match_data->options = original_options;
     if (rc >= 0 && (options & PCRE2_COPY_MATCHED_SUBJECT) != 0)
       {
-      length = CU2BYTES(length + was_zero_terminated);
-      match_data->subject = match_data->memctl.malloc(length,
-        match_data->memctl.memory_data);
-      if (match_data->subject == NULL)
-        return match_data->rc = PCRE2_ERROR_NOMEMORY;
-      memcpy((void *)match_data->subject, subject, length);
+      if (length != 0)
+        {
+        match_data->subject = match_data->memctl.malloc(CU2BYTES(length),
+          match_data->memctl.memory_data);
+        if (match_data->subject == NULL)
+          return match_data->rc = PCRE2_ERROR_NOMEMORY;
+        memcpy((void *)match_data->subject, subject, CU2BYTES(length));
+        }
+      else
+        match_data->subject = NULL;
       match_data->flags |= PCRE2_MD_COPIED_SUBJECT;
       }
     else
@@ -8155,12 +8157,16 @@ if (rc == MATCH_MATCH)
     mb->last_used_ptr : mb->end_match_ptr) - subject;
   if ((options & PCRE2_COPY_MATCHED_SUBJECT) != 0)
     {
-    length = CU2BYTES(length + was_zero_terminated);
-    match_data->subject = match_data->memctl.malloc(length,
-      match_data->memctl.memory_data);
-    if (match_data->subject == NULL)
-      return match_data->rc = PCRE2_ERROR_NOMEMORY;
-    memcpy((void *)match_data->subject, subject, length);
+    if (length != 0)
+      {
+      match_data->subject = match_data->memctl.malloc(CU2BYTES(length),
+        match_data->memctl.memory_data);
+      if (match_data->subject == NULL)
+        return match_data->rc = PCRE2_ERROR_NOMEMORY;
+      memcpy((void *)match_data->subject, subject, CU2BYTES(length));
+      }
+    else
+      match_data->subject = NULL;
     match_data->flags |= PCRE2_MD_COPIED_SUBJECT;
     }
   else match_data->subject = original_subject;

src/pcre2test_inc.h

@@ -2533,6 +2533,7 @@ if (pat_patctl.convert_type != CONVERT_UNSET)
 
   // TODO No valgrind guards for out-of-bounds read in pcre2_pattern_convert(),
   // nor do we appear to have a facility for testing zero-terminated patterns here.
+  // Can we use something other than zero as a sentinel to allow testing empty inputs?
 
   if (pat_patctl.convert_length != 0)
     {