[glibc/release/2.34/master] regex: copy back from Gnulib

[glibc/release/2.34/master] regex: copy back from Gnulib

[Florian Weimer]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=86a701a20479dfbc23540b3143fd5b28660a2447

commit 86a701a20479dfbc23540b3143fd5b28660a2447
Author: Paul Eggert <eggert@cs.ucla.edu>
Date:   Tue Sep 21 07:47:45 2021 -0700

    regex: copy back from Gnulib
    
    Copy regex-related files back from Gnulib, to fix a problem with
    static checking of regex calls noted by Martin Sebor.  This merges the
    following changes:
    
    * New macro __attribute_nonnull__ in misc/sys/cdefs.h, for use later
    when copying other files back from Gnulib.
    
    * Use __GNULIB_CDEFS instead of __GLIBC__ when deciding
    whether to include bits/wordsize.h etc.
    
    * Avoid duplicate entries in epsilon closure table.
    
    * New regex.h macro _REGEX_NELTS to let regexec say that its pmatch
    arg should contain nmatch elts.  Use that for regexec, instead of
    __attr_access (which is incorrect).
    
    * New regex.h macro _Attr_access_ which is like __attr_access except
    portable to non-glibc platforms.
    
    * Add some DEBUG_ASSERTs to pacify gcc -fanalyzer and to catch
    recently-fixed performance bugs if they recur.
    
    * Add Gnulib-specific stuff to port the dynarray- and lock-using parts
    of regex code to non-glibc platforms.
    
    * Fix glibc bug 11053.
    
    * Avoid some undefined behavior when popping an empty fail stack.
    
    (cherry picked from commit 0b5ca7c3e551e5502f3be3b06453324fe8604e82)

Diff:
---
 NEWS                   |   1 +
 include/intprops.h     |  18 +++++++--
 include/regex.h        |   3 +-
 misc/sys/cdefs.h       |  22 ++++++-----
 posix/regcomp.c        |   8 ++--
 posix/regex.c          |   1 +
 posix/regex.h          |  49 ++++++++++++++++++------
 posix/regex_internal.c |  10 ++++-
 posix/regex_internal.h |   8 +++-
 posix/regexec.c        | 101 ++++++++++++++++++++++++++++---------------------
 10 files changed, 143 insertions(+), 78 deletions(-)

diff --git a/NEWS b/NEWS
index b4811098c8..8329b2454c 100644
--- a/NEWS
+++ b/NEWS
@@ -48,6 +48,7 @@ Security related changes:
 
 The following bugs are resolved with this release:
 
+  [11053] regex: Wrong results with backreferences
   [12154] Do not fail DNS resolution for CNAMEs which are not host names
   [12889] nptl: Fix race between pthread_kill and thread exit
   [15533] dynamic-link: LD_AUDIT introduces an avoidable performance
diff --git a/include/intprops.h b/include/intprops.h
index 967e32ea0c..9d10028a59 100644
--- a/include/intprops.h
+++ b/include/intprops.h
@@ -133,7 +133,8 @@
    operators might not yield numerically correct answers due to
    arithmetic overflow.  They do not rely on undefined or
    implementation-defined behavior.  Their implementations are simple
-   and straightforward, but they are a bit harder to use than the
+   and straightforward, but they are harder to use and may be less
+   efficient than the INT_<op>_WRAPV, INT_<op>_OK, and
    INT_<op>_OVERFLOW macros described below.
 
    Example usage:
@@ -158,6 +159,9 @@
    must have minimum value MIN and maximum MAX.  Unsigned types should
    use a zero MIN of the proper type.
 
+   Because all arguments are subject to integer promotions, these
+   macros typically do not work on types narrower than 'int'.
+
    These macros are tuned for constant MIN and MAX.  For commutative
    operations such as A + B, they are also tuned for constant B.  */
 
@@ -339,9 +343,15 @@
    arguments should not have side effects.
 
    The WRAPV macros are not constant expressions.  They support only
-   +, binary -, and *.  Because the WRAPV macros convert the result,
-   they report overflow in different circumstances than the OVERFLOW
-   macros do.
+   +, binary -, and *.
+
+   Because the WRAPV macros convert the result, they report overflow
+   in different circumstances than the OVERFLOW macros do.  For
+   example, in the typical case with 16-bit 'short' and 32-bit 'int',
+   if A, B and R are all of type 'short' then INT_ADD_OVERFLOW (A, B)
+   returns false because the addition cannot overflow after A and B
+   are converted to 'int', whereas INT_ADD_WRAPV (A, B, &R) returns
+   true or false depending on whether the sum fits into 'short'.
 
    These macros are tuned for their last input argument being a constant.
 
diff --git a/include/regex.h b/include/regex.h
index 24eca2c297..34fb67d855 100644
--- a/include/regex.h
+++ b/include/regex.h
@@ -37,7 +37,8 @@ extern int __regcomp (regex_t *__preg, const char *__pattern, int __cflags);
 libc_hidden_proto (__regcomp)
 
 extern int __regexec (const regex_t *__preg, const char *__string,
-		      size_t __nmatch, regmatch_t __pmatch[], int __eflags);
+		      size_t __nmatch, regmatch_t __pmatch[__nmatch],
+		      int __eflags);
 libc_hidden_proto (__regexec)
 
 extern size_t __regerror (int __errcode, const regex_t *__preg,
diff --git a/misc/sys/cdefs.h b/misc/sys/cdefs.h
index e0ecd9147e..b166f3d209 100644
--- a/misc/sys/cdefs.h
+++ b/misc/sys/cdefs.h
@@ -366,16 +366,18 @@
 #endif
 
 /* The nonnull function attribute marks pointer parameters that
-   must not be NULL.  */
-#ifndef __nonnull
+   must not be NULL.  This has the name __nonnull in glibc,
+   and __attribute_nonnull__ in files shared with Gnulib to avoid
+   collision with a different __nonnull in DragonFlyBSD 5.9.  */
+#ifndef __attribute_nonnull__
 # if __GNUC_PREREQ (3,3) || __glibc_has_attribute (__nonnull__)
-#  define __nonnull(params) __attribute__ ((__nonnull__ params))
+#  define __attribute_nonnull__(params) __attribute__ ((__nonnull__ params))
 # else
-#  define __nonnull(params)
+#  define __attribute_nonnull__(params)
 # endif
-#elif !defined __GLIBC__
-# undef __nonnull
-# define __nonnull(params) _GL_ATTRIBUTE_NONNULL (params)
+#endif
+#ifndef __nonnull
+# define __nonnull(params) __attribute_nonnull__ (params)
 #endif
 
 /* The returns_nonnull function attribute marks the return type of the function
@@ -541,9 +543,9 @@
       [!!sizeof (struct { int __error_if_negative: (expr) ? 2 : -1; })]
 #endif
 
-/* The #ifndef lets Gnulib avoid including these on non-glibc
-   platforms, where the includes typically do not exist.  */
-#ifdef __GLIBC__
+/* Gnulib avoids including these, as they don't work on non-glibc or
+   older glibc platforms.  */
+#ifndef __GNULIB_CDEFS
 # include <bits/wordsize.h>
 # include <bits/long-double.h>
 #endif
diff --git a/posix/regcomp.c b/posix/regcomp.c
index d93698ae78..887e5b5068 100644
--- a/posix/regcomp.c
+++ b/posix/regcomp.c
@@ -1695,12 +1695,14 @@ calc_eclosure_iter (re_node_set *new_set, re_dfa_t *dfa, Idx node, bool root)
   reg_errcode_t err;
   Idx i;
   re_node_set eclosure;
-  bool ok;
   bool incomplete = false;
   err = re_node_set_alloc (&eclosure, dfa->edests[node].nelem + 1);
   if (__glibc_unlikely (err != REG_NOERROR))
     return err;
 
+  /* An epsilon closure includes itself.  */
+  eclosure.elems[eclosure.nelem++] = node;
+
   /* This indicates that we are calculating this node now.
      We reference this value to avoid infinite loop.  */
   dfa->eclosures[node].nelem = -1;
@@ -1753,10 +1755,6 @@ calc_eclosure_iter (re_node_set *new_set, re_dfa_t *dfa, Idx node, bool root)
 	  }
       }
 
-  /* An epsilon closure includes itself.  */
-  ok = re_node_set_insert (&eclosure, node);
-  if (__glibc_unlikely (! ok))
-    return REG_ESPACE;
   if (incomplete && !root)
     dfa->eclosures[node].nelem = 0;
   else
diff --git a/posix/regex.c b/posix/regex.c
index 7296be0f08..d32863972c 100644
--- a/posix/regex.c
+++ b/posix/regex.c
@@ -24,6 +24,7 @@
 
 # if __GNUC_PREREQ (4, 6)
 #  pragma GCC diagnostic ignored "-Wsuggest-attribute=pure"
+#  pragma GCC diagnostic ignored "-Wvla"
 # endif
 # if __GNUC_PREREQ (4, 3)
 #  pragma GCC diagnostic ignored "-Wold-style-definition"
diff --git a/posix/regex.h b/posix/regex.h
index 14fb1d8364..adb69768ee 100644
--- a/posix/regex.h
+++ b/posix/regex.h
@@ -522,6 +522,30 @@ typedef struct
 \f
 /* Declarations for routines.  */
 
+#ifndef _REGEX_NELTS
+# if (defined __STDC_VERSION__ && 199901L <= __STDC_VERSION__ \
+	&& !defined __STDC_NO_VLA__)
+#  define _REGEX_NELTS(n) n
+# else
+#  define _REGEX_NELTS(n)
+# endif
+#endif
+
+#if defined __GNUC__ && 4 < __GNUC__ + (6 <= __GNUC_MINOR__)
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Wvla"
+#endif
+
+#ifndef _Attr_access_
+# ifdef __attr_access
+#  define _Attr_access_(arg) __attr_access (arg)
+# elif defined __GNUC__ && 10 <= __GNUC__
+#  define _Attr_access_(x) __attribute__ ((__access__ x))
+# else
+#  define _Attr_access_(x)
+# endif
+#endif
+
 #ifdef __USE_GNU
 /* Sets the current default syntax to SYNTAX, and return the old syntax.
    You can also simply assign to the 're_syntax_options' variable.  */
@@ -537,7 +561,7 @@ extern reg_syntax_t re_set_syntax (reg_syntax_t __syntax);
    'regfree'.  */
 extern const char *re_compile_pattern (const char *__pattern, size_t __length,
 				       struct re_pattern_buffer *__buffer)
-    __attr_access ((__read_only__, 1, 2));
+    _Attr_access_ ((__read_only__, 1, 2));
 
 
 /* Compile a fastmap for the compiled pattern in BUFFER; used to
@@ -555,7 +579,7 @@ extern regoff_t re_search (struct re_pattern_buffer *__buffer,
 			   const char *__String, regoff_t __length,
 			   regoff_t __start, regoff_t __range,
 			   struct re_registers *__regs)
-    __attr_access ((__read_only__, 2, 3));
+    _Attr_access_ ((__read_only__, 2, 3));
 
 
 /* Like 're_search', but search in the concatenation of STRING1 and
@@ -566,8 +590,8 @@ extern regoff_t re_search_2 (struct re_pattern_buffer *__buffer,
 			     regoff_t __start, regoff_t __range,
 			     struct re_registers *__regs,
 			     regoff_t __stop)
-    __attr_access ((__read_only__, 2, 3))
-    __attr_access ((__read_only__, 4, 5));
+    _Attr_access_ ((__read_only__, 2, 3))
+    _Attr_access_ ((__read_only__, 4, 5));
 
 
 /* Like 're_search', but return how many characters in STRING the regexp
@@ -575,7 +599,7 @@ extern regoff_t re_search_2 (struct re_pattern_buffer *__buffer,
 extern regoff_t re_match (struct re_pattern_buffer *__buffer,
 			  const char *__String, regoff_t __length,
 			  regoff_t __start, struct re_registers *__regs)
-    __attr_access ((__read_only__, 2, 3));
+    _Attr_access_ ((__read_only__, 2, 3));
 
 
 /* Relates to 're_match' as 're_search_2' relates to 're_search'.  */
@@ -584,8 +608,8 @@ extern regoff_t re_match_2 (struct re_pattern_buffer *__buffer,
 			    const char *__string2, regoff_t __length2,
 			    regoff_t __start, struct re_registers *__regs,
 			    regoff_t __stop)
-    __attr_access ((__read_only__, 2, 3))
-    __attr_access ((__read_only__, 4, 5));
+    _Attr_access_ ((__read_only__, 2, 3))
+    _Attr_access_ ((__read_only__, 4, 5));
 
 
 /* Set REGS to hold NUM_REGS registers, storing them in STARTS and
@@ -654,16 +678,19 @@ extern int regcomp (regex_t *_Restrict_ __preg,
 
 extern int regexec (const regex_t *_Restrict_ __preg,
 		    const char *_Restrict_ __String, size_t __nmatch,
-		    regmatch_t __pmatch[_Restrict_arr_],
-		    int __eflags)
-    __attr_access ((__write_only__, 4, 3));
+		    regmatch_t __pmatch[_Restrict_arr_
+					_REGEX_NELTS (__nmatch)],
+		    int __eflags);
 
 extern size_t regerror (int __errcode, const regex_t *_Restrict_ __preg,
 			char *_Restrict_ __errbuf, size_t __errbuf_size)
-    __attr_access ((__write_only__, 3, 4));
+    _Attr_access_ ((__write_only__, 3, 4));
 
 extern void regfree (regex_t *__preg);
 
+#if defined __GNUC__ && 4 < __GNUC__ + (6 <= __GNUC_MINOR__)
+# pragma GCC diagnostic pop
+#endif
 
 #ifdef __cplusplus
 }
diff --git a/posix/regex_internal.c b/posix/regex_internal.c
index 9dd387ef85..aefcfa2f52 100644
--- a/posix/regex_internal.c
+++ b/posix/regex_internal.c
@@ -1211,6 +1211,10 @@ re_node_set_merge (re_node_set *dest, const re_node_set *src)
 
   if (__glibc_unlikely (dest->nelem == 0))
     {
+      /* Although we already guaranteed above that dest->alloc != 0 and
+         therefore dest->elems != NULL, add a debug assertion to pacify
+         GCC 11.2.1's -fanalyzer.  */
+      DEBUG_ASSERT (dest->elems);
       dest->nelem = src->nelem;
       memcpy (dest->elems, src->elems, src->nelem * sizeof (Idx));
       return REG_NOERROR;
@@ -1286,7 +1290,10 @@ re_node_set_insert (re_node_set *set, Idx elem)
 
   if (__glibc_unlikely (set->nelem) == 0)
     {
-      /* We already guaranteed above that set->alloc != 0.  */
+      /* Although we already guaranteed above that set->alloc != 0 and
+         therefore set->elems != NULL, add a debug assertion to pacify
+         GCC 11.2 -fanalyzer.  */
+      DEBUG_ASSERT (set->elems);
       set->elems[0] = elem;
       ++set->nelem;
       return true;
@@ -1314,6 +1321,7 @@ re_node_set_insert (re_node_set *set, Idx elem)
     {
       for (idx = set->nelem; set->elems[idx - 1] > elem; idx--)
 	set->elems[idx] = set->elems[idx - 1];
+      DEBUG_ASSERT (set->elems[idx - 1] < elem);
     }
 
   /* Insert the new element.  */
diff --git a/posix/regex_internal.h b/posix/regex_internal.h
index edcdc07e99..1245e782ff 100644
--- a/posix/regex_internal.h
+++ b/posix/regex_internal.h
@@ -32,6 +32,10 @@
 #include <stdbool.h>
 #include <stdint.h>
 
+#ifndef _LIBC
+# include <dynarray.h>
+#endif
+
 #include <intprops.h>
 #include <verify.h>
 
@@ -49,14 +53,14 @@
 # define lock_fini(lock) ((void) 0)
 # define lock_lock(lock) __libc_lock_lock (lock)
 # define lock_unlock(lock) __libc_lock_unlock (lock)
-#elif defined GNULIB_LOCK && !defined USE_UNLOCKED_IO
+#elif defined GNULIB_LOCK && !defined GNULIB_REGEX_SINGLE_THREAD
 # include "glthread/lock.h"
 # define lock_define(name) gl_lock_define (, name)
 # define lock_init(lock) glthread_lock_init (&(lock))
 # define lock_fini(lock) glthread_lock_destroy (&(lock))
 # define lock_lock(lock) glthread_lock_lock (&(lock))
 # define lock_unlock(lock) glthread_lock_unlock (&(lock))
-#elif defined GNULIB_PTHREAD && !defined USE_UNLOCKED_IO
+#elif defined GNULIB_PTHREAD && !defined GNULIB_REGEX_SINGLE_THREAD
 # include <pthread.h>
 # define lock_define(name) pthread_mutex_t name;
 # define lock_init(lock) pthread_mutex_init (&(lock), 0)
diff --git a/posix/regexec.c b/posix/regexec.c
index f7b4f9cfc3..83e9aaf8ca 100644
--- a/posix/regexec.c
+++ b/posix/regexec.c
@@ -59,7 +59,7 @@ static void update_regs (const re_dfa_t *dfa, regmatch_t *pmatch,
 			 Idx cur_idx, Idx nmatch);
 static reg_errcode_t push_fail_stack (struct re_fail_stack_t *fs,
 				      Idx str_idx, Idx dest_node, Idx nregs,
-				      regmatch_t *regs,
+				      regmatch_t *regs, regmatch_t *prevregs,
 				      re_node_set *eps_via_nodes);
 static reg_errcode_t set_regs (const regex_t *preg,
 			       const re_match_context_t *mctx,
@@ -186,11 +186,12 @@ static reg_errcode_t extend_buffers (re_match_context_t *mctx, int min_len);
    REG_NOTBOL is set, then ^ does not match at the beginning of the
    string; if REG_NOTEOL is set, then $ does not match at the end.
 
-   We return 0 if we find a match and REG_NOMATCH if not.  */
+   Return 0 if a match is found, REG_NOMATCH if not, REG_BADPAT if
+   EFLAGS is invalid.  */
 
 int
 regexec (const regex_t *__restrict preg, const char *__restrict string,
-	 size_t nmatch, regmatch_t pmatch[], int eflags)
+	 size_t nmatch, regmatch_t pmatch[_REGEX_NELTS (nmatch)], int eflags)
 {
   reg_errcode_t err;
   Idx start, length;
@@ -234,7 +235,7 @@ int
 attribute_compat_text_section
 __compat_regexec (const regex_t *__restrict preg,
 		  const char *__restrict string, size_t nmatch,
-		  regmatch_t pmatch[], int eflags)
+		  regmatch_t pmatch[_REGEX_NELTS (nmatch)], int eflags)
 {
   return regexec (preg, string, nmatch, pmatch,
 		  eflags & (REG_NOTBOL | REG_NOTEOL));
@@ -269,8 +270,8 @@ compat_symbol (libc, __compat_regexec, regexec, GLIBC_2_0);
    strings.)
 
    On success, re_match* functions return the length of the match, re_search*
-   return the position of the start of the match.  Return value -1 means no
-   match was found and -2 indicates an internal error.  */
+   return the position of the start of the match.  They return -1 on
+   match failure, -2 on error.  */
 
 regoff_t
 re_match (struct re_pattern_buffer *bufp, const char *string, Idx length,
@@ -1206,27 +1207,30 @@ check_halt_state_context (const re_match_context_t *mctx,
 /* Compute the next node to which "NFA" transit from NODE("NFA" is a NFA
    corresponding to the DFA).
    Return the destination node, and update EPS_VIA_NODES;
-   return -1 in case of errors.  */
+   return -1 on match failure, -2 on error.  */
 
 static Idx
 proceed_next_node (const re_match_context_t *mctx, Idx nregs, regmatch_t *regs,
+		   regmatch_t *prevregs,
 		   Idx *pidx, Idx node, re_node_set *eps_via_nodes,
 		   struct re_fail_stack_t *fs)
 {
   const re_dfa_t *const dfa = mctx->dfa;
-  Idx i;
-  bool ok;
   if (IS_EPSILON_NODE (dfa->nodes[node].type))
     {
       re_node_set *cur_nodes = &mctx->state_log[*pidx]->nodes;
       re_node_set *edests = &dfa->edests[node];
-      Idx dest_node;
-      ok = re_node_set_insert (eps_via_nodes, node);
-      if (__glibc_unlikely (! ok))
-	return -2;
-      /* Pick up a valid destination, or return -1 if none
-	 is found.  */
-      for (dest_node = -1, i = 0; i < edests->nelem; ++i)
+
+      if (! re_node_set_contains (eps_via_nodes, node))
+        {
+          bool ok = re_node_set_insert (eps_via_nodes, node);
+          if (__glibc_unlikely (! ok))
+            return -2;
+        }
+
+      /* Pick a valid destination, or return -1 if none is found.  */
+      Idx dest_node = -1;
+      for (Idx i = 0; i < edests->nelem; i++)
 	{
 	  Idx candidate = edests->elems[i];
 	  if (!re_node_set_contains (cur_nodes, candidate))
@@ -1244,7 +1248,7 @@ proceed_next_node (const re_match_context_t *mctx, Idx nregs, regmatch_t *regs,
 	      /* Otherwise, push the second epsilon-transition on the fail stack.  */
 	      else if (fs != NULL
 		       && push_fail_stack (fs, *pidx, candidate, nregs, regs,
-					   eps_via_nodes))
+					   prevregs, eps_via_nodes))
 		return -2;
 
 	      /* We know we are going to exit.  */
@@ -1288,7 +1292,7 @@ proceed_next_node (const re_match_context_t *mctx, Idx nregs, regmatch_t *regs,
 	  if (naccepted == 0)
 	    {
 	      Idx dest_node;
-	      ok = re_node_set_insert (eps_via_nodes, node);
+	      bool ok = re_node_set_insert (eps_via_nodes, node);
 	      if (__glibc_unlikely (! ok))
 		return -2;
 	      dest_node = dfa->edests[node].elems[0];
@@ -1317,7 +1321,8 @@ proceed_next_node (const re_match_context_t *mctx, Idx nregs, regmatch_t *regs,
 static reg_errcode_t
 __attribute_warn_unused_result__
 push_fail_stack (struct re_fail_stack_t *fs, Idx str_idx, Idx dest_node,
-		 Idx nregs, regmatch_t *regs, re_node_set *eps_via_nodes)
+		 Idx nregs, regmatch_t *regs, regmatch_t *prevregs,
+		 re_node_set *eps_via_nodes)
 {
   reg_errcode_t err;
   Idx num = fs->num++;
@@ -1333,25 +1338,30 @@ push_fail_stack (struct re_fail_stack_t *fs, Idx str_idx, Idx dest_node,
     }
   fs->stack[num].idx = str_idx;
   fs->stack[num].node = dest_node;
-  fs->stack[num].regs = re_malloc (regmatch_t, nregs);
+  fs->stack[num].regs = re_malloc (regmatch_t, 2 * nregs);
   if (fs->stack[num].regs == NULL)
     return REG_ESPACE;
   memcpy (fs->stack[num].regs, regs, sizeof (regmatch_t) * nregs);
+  memcpy (fs->stack[num].regs + nregs, prevregs, sizeof (regmatch_t) * nregs);
   err = re_node_set_init_copy (&fs->stack[num].eps_via_nodes, eps_via_nodes);
   return err;
 }
 
 static Idx
 pop_fail_stack (struct re_fail_stack_t *fs, Idx *pidx, Idx nregs,
-		regmatch_t *regs, re_node_set *eps_via_nodes)
+		regmatch_t *regs, regmatch_t *prevregs,
+		re_node_set *eps_via_nodes)
 {
+  if (fs == NULL || fs->num == 0)
+    return -1;
   Idx num = --fs->num;
-  DEBUG_ASSERT (num >= 0);
   *pidx = fs->stack[num].idx;
   memcpy (regs, fs->stack[num].regs, sizeof (regmatch_t) * nregs);
+  memcpy (prevregs, fs->stack[num].regs + nregs, sizeof (regmatch_t) * nregs);
   re_node_set_free (eps_via_nodes);
   re_free (fs->stack[num].regs);
   *eps_via_nodes = fs->stack[num].eps_via_nodes;
+  DEBUG_ASSERT (0 <= fs->stack[num].node);
   return fs->stack[num].node;
 }
 
@@ -1407,33 +1417,32 @@ set_regs (const regex_t *preg, const re_match_context_t *mctx, size_t nmatch,
     {
       update_regs (dfa, pmatch, prev_idx_match, cur_node, idx, nmatch);
 
-      if (idx == pmatch[0].rm_eo && cur_node == mctx->last_node)
+      if ((idx == pmatch[0].rm_eo && cur_node == mctx->last_node)
+	  || (fs && re_node_set_contains (&eps_via_nodes, cur_node)))
 	{
 	  Idx reg_idx;
+	  cur_node = -1;
 	  if (fs)
 	    {
 	      for (reg_idx = 0; reg_idx < nmatch; ++reg_idx)
 		if (pmatch[reg_idx].rm_so > -1 && pmatch[reg_idx].rm_eo == -1)
-		  break;
-	      if (reg_idx == nmatch)
-		{
-		  re_node_set_free (&eps_via_nodes);
-		  regmatch_list_free (&prev_match);
-		  return free_fail_stack_return (fs);
-		}
-	      cur_node = pop_fail_stack (fs, &idx, nmatch, pmatch,
-					 &eps_via_nodes);
+		  {
+		    cur_node = pop_fail_stack (fs, &idx, nmatch, pmatch,
+					       prev_idx_match, &eps_via_nodes);
+		    break;
+		  }
 	    }
-	  else
+	  if (cur_node < 0)
 	    {
 	      re_node_set_free (&eps_via_nodes);
 	      regmatch_list_free (&prev_match);
-	      return REG_NOERROR;
+	      return free_fail_stack_return (fs);
 	    }
 	}
 
       /* Proceed to next node.  */
-      cur_node = proceed_next_node (mctx, nmatch, pmatch, &idx, cur_node,
+      cur_node = proceed_next_node (mctx, nmatch, pmatch, prev_idx_match,
+				    &idx, cur_node,
 				    &eps_via_nodes, fs);
 
       if (__glibc_unlikely (cur_node < 0))
@@ -1445,13 +1454,13 @@ set_regs (const regex_t *preg, const re_match_context_t *mctx, size_t nmatch,
 	      free_fail_stack_return (fs);
 	      return REG_ESPACE;
 	    }
-	  if (fs)
-	    cur_node = pop_fail_stack (fs, &idx, nmatch, pmatch,
-				       &eps_via_nodes);
-	  else
+	  cur_node = pop_fail_stack (fs, &idx, nmatch, pmatch,
+				     prev_idx_match, &eps_via_nodes);
+	  if (cur_node < 0)
 	    {
 	      re_node_set_free (&eps_via_nodes);
 	      regmatch_list_free (&prev_match);
+	      free_fail_stack_return (fs);
 	      return REG_NOMATCH;
 	    }
 	}
@@ -1495,10 +1504,10 @@ update_regs (const re_dfa_t *dfa, regmatch_t *pmatch,
     }
   else if (type == OP_CLOSE_SUBEXP)
     {
+      /* We are at the last node of this sub expression.  */
       Idx reg_num = dfa->nodes[cur_node].opr.idx + 1;
       if (reg_num < nmatch)
 	{
-	  /* We are at the last node of this sub expression.  */
 	  if (pmatch[reg_num].rm_so < cur_idx)
 	    {
 	      pmatch[reg_num].rm_eo = cur_idx;
@@ -2195,6 +2204,7 @@ sift_states_iter_mb (const re_match_context_t *mctx, re_sift_context_t *sctx,
 
 /* Return the next state to which the current state STATE will transit by
    accepting the current input byte, and update STATE_LOG if necessary.
+   Return NULL on failure.
    If STATE can accept a multibyte char/collating element/back reference
    update the destination of STATE_LOG.  */
 
@@ -2395,7 +2405,7 @@ check_subexp_matching_top (re_match_context_t *mctx, re_node_set *cur_nodes,
 
 #if 0
 /* Return the next state to which the current state STATE will transit by
-   accepting the current input byte.  */
+   accepting the current input byte.  Return NULL on failure.  */
 
 static re_dfastate_t *
 transit_state_sb (reg_errcode_t *err, re_match_context_t *mctx,
@@ -2817,7 +2827,8 @@ find_subexp_node (const re_dfa_t *dfa, const re_node_set *nodes,
 /* Check whether the node TOP_NODE at TOP_STR can arrive to the node
    LAST_NODE at LAST_STR.  We record the path onto PATH since it will be
    heavily reused.
-   Return REG_NOERROR if it can arrive, or REG_NOMATCH otherwise.  */
+   Return REG_NOERROR if it can arrive, REG_NOMATCH if it cannot,
+   REG_ESPACE if memory is exhausted.  */
 
 static reg_errcode_t
 __attribute_warn_unused_result__
@@ -3433,7 +3444,8 @@ build_trtable (const re_dfa_t *dfa, re_dfastate_t *state)
 /* Group all nodes belonging to STATE into several destinations.
    Then for all destinations, set the nodes belonging to the destination
    to DESTS_NODE[i] and set the characters accepted by the destination
-   to DEST_CH[i].  This function return the number of destinations.  */
+   to DEST_CH[i].  Return the number of destinations if successful,
+   -1 on internal error.  */
 
 static Idx
 group_nodes_into_DFAstates (const re_dfa_t *dfa, const re_dfastate_t *state,
@@ -4211,7 +4223,8 @@ match_ctx_add_subtop (re_match_context_t *mctx, Idx node, Idx str_idx)
 }
 
 /* Register the node NODE, whose type is OP_CLOSE_SUBEXP, and which matches
-   at STR_IDX, whose corresponding OP_OPEN_SUBEXP is SUB_TOP.  */
+   at STR_IDX, whose corresponding OP_OPEN_SUBEXP is SUB_TOP.
+   Return the new entry if successful, NULL if memory is exhausted.  */
 
 static re_sub_match_last_t *
 match_ctx_add_sublast (re_sub_match_top_t *subtop, Idx node, Idx str_idx)