GCC 10 warning stringop-overflow with symbol code

On 18/06/2020 8:46 am, Koichi Sakata wrote:
Hi all,

I tried to build OpenJDK fastdebug with GCC 10.1 on Ubuntu 18.04, but I saw some compiler warnings as follows:

In file included from
/home/jyukutyo/code/jdk/src/hotspot/share/classfile/systemDictionary.hpp:31,
                  from
/home/jyukutyo/code/jdk/src/hotspot/share/classfile/javaClasses.hpp:28,
                  from
/home/jyukutyo/code/jdk/src/hotspot/share/precompiled/precompiled.hpp:35:
In member function 'void Symbol::byte_at_put(int, u1)',
     inlined from 'Symbol::Symbol(const u1*, int, int)' at
/home/jyukutyo/code/jdk/src/hotspot/share/oops/symbol.cpp:55:16:
/home/jyukutyo/code/jdk/src/hotspot/share/oops/symbol.hpp:130:18: error:
writing 1 byte into a region of size 0 [-Werror=stringop-overflow=]
   130 | _body[index] = value;
       | ~~~~~~~~~~~~~^~~~~~~

I can resolve them with the following patch. I believe it fixes those potential bugs, so I'd like to contribute it.
(Our company has signed OCA.)

Thanks,
Koichi

===== PATCH =====
diff -r 20d92fe3ac52 src/hotspot/share/oops/symbol.cpp
--- a/src/hotspot/share/oops/symbol.cpp Tue Jun 16 03:16:41 2020 +0000
+++ b/src/hotspot/share/oops/symbol.cpp Thu Jun 18 07:08:50 2020 +0900
@@ -50,9 +50,10 @@
 Symbol::Symbol(const u1* name, int length, int refcount) {
   _hash_and_refcount = pack_hash_and_refcount((short)os::random(), refcount);
   _length = length;
- _body[0] = 0; // in case length == 0
- for (int i = 0; i < length; i++) {
- byte_at_put(i, name[i]);
+ if (length == 0) {
+ _body[0] = 0;
+ } else {
+ memcpy(_body, name, length);
   }
 }

diff -r 20d92fe3ac52 src/hotspot/share/oops/symbol.hpp
--- a/src/hotspot/share/oops/symbol.hpp Tue Jun 16 03:16:41 2020 +0000
+++ b/src/hotspot/share/oops/symbol.hpp Thu Jun 18 07:08:50 2020 +0900
@@ -125,11 +125,6 @@
     return (int)heap_word_size(byte_size(length));
   }

- void byte_at_put(int index, u1 value) {
- assert(index >=0 && index < length(), "symbol index overflow");
- _body[index] = value;
- }
-
   Symbol(const u1* name, int length, int refcount);
   void* operator new(size_t size, int len) throw();
   void* operator new(size_t size, int len, Arena* arena) throw();