[gcc r14-2990] gensupport: Don't segfault on empty attrs list

[gcc r14-2990] gensupport: Don't segfault on empty attrs list

[Tamar Christina]

https://gcc.gnu.org/g:6b80071a4d05c9535d3bb26cddaed0895a414f59

commit r14-2990-g6b80071a4d05c9535d3bb26cddaed0895a414f59
Author: Tamar Christina <tamar.christina@arm.com>
Date:   Fri Aug 4 13:48:56 2023 +0100

    gensupport: Don't segfault on empty attrs list
    
    Currently we segfault when len == 0 for an attribute list.
    
    essentially [cons: =0, 1, 2, 3; attrs: ] segfaults but should be equivalent to
    [cons: =0, 1, 2, 3] and [cons: =0, 1, 2, 3; attrs:].  This fixes it by just
    returning early and leaving it to the validators whether this should error out
    or not.
    
    gcc/ChangeLog:
    
            * gensupport.cc (conlist): Support length 0 attribute.

Diff:
---
 gcc/gensupport.cc | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/gcc/gensupport.cc b/gcc/gensupport.cc
index 959d1d9c83c..b2feb03363a 100644
--- a/gcc/gensupport.cc
+++ b/gcc/gensupport.cc
@@ -620,7 +620,7 @@ public:
   conlist (const char *ns, unsigned int len, bool numeric)
   {
     /* Trim leading whitespaces.  */
-    while (ISBLANK (*ns))
+    while (len > 0 && ISBLANK (*ns))
       {
 	ns++;
 	len--;
@@ -632,7 +632,7 @@ public:
 	break;
 
     /* Parse off any modifiers.  */
-    while (!ISALNUM (*ns))
+    while (len > 0 && !ISALNUM (*ns))
       {
 	con += *(ns++);
 	len--;