https://mail.openjdk.java.net/pipermail/core-libs-dev/2020-June/067445.html

Koichi Sakata <sakatakui@oss.nttdata.com> reported:

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

/home/jyukutyo/code/jdk/src/java.base/share/native/libfdlibm/: In
function '__j__kernel_standard':
/home/jyukutyo/code/jdk/src/java.base/share/native/libfdlibm/k_standard.c:743:19:
error: 'exc.retval' may be used uninitialized in this function
[-Werror=maybe-uninitialized]
   743 | return exc.retval;
       | ~~~^~~~~~~

In file included from /usr/include/string.h:494,
                  from
/home/jyukutyo/code/jdk/src/java.base/unix/native/libnet/NetworkInterface.c:30:
In function 'strncpy',
     inlined from 'getFlags' at
/home/jyukutyo/code/jdk/src/java.base/unix/native/libnet/NetworkInterface.c:1362:5,
     inlined from 'addif' at
/home/jyukutyo/code/jdk/src/java.base/unix/native/libnet/NetworkInterface.c:974:13:
/usr/include/x86_64-linux-gnu/bits/string_fortified.h:106:10: error:
'__builtin_strncpy' output may be truncated copying 15 bytes from a
string of length 15 [-Werror=stringop-truncation]
   106 | return __builtin___strncpy_chk (__dest, __src, __len, __bos
(__dest));
       | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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/java.base/share/native/libfdlibm/k_standard.c
--- a/src/java.base/share/native/libfdlibm/k_standard.c Tue Jun 16
03:16:41 2020 +0000
+++ b/src/java.base/share/native/libfdlibm/k_standard.c Thu Jun 18
07:08:50 2020 +0900
@@ -739,6 +739,10 @@
                          errno = EDOM;
                  }
                  break;
+ default:
+ exc.retval = zero;
+ errno = EINVAL;
+ break;
          }
          return exc.retval;
  }
diff -r 20d92fe3ac52 src/java.base/unix/native/libnet/NetworkInterface.c
--- a/src/java.base/unix/native/libnet/NetworkInterface.c Tue Jun
16 03:16:41 2020 +0000
+++ b/src/java.base/unix/native/libnet/NetworkInterface.c Thu Jun
18 07:08:50 2020 +0900
@@ -1296,7 +1296,10 @@
  static int getIndex(int sock, const char *name) {
      struct ifreq if2;
      memset((char *)&if2, 0, sizeof(if2));
- strncpy(if2.ifr_name, name, sizeof(if2.ifr_name) - 1);
+ if (sizeof(if2.ifr_name) < sizeof(name)) {
+ return -1;
+ }
+ strcpy(if2.ifr_name, name);

      if (ioctl(sock, SIOCGIFINDEX, (char *)&if2) < 0) {
          return -1;
@@ -1359,7 +1362,10 @@
  static int getFlags(int sock, const char *ifname, int *flags) {
      struct ifreq if2;
      memset((char *)&if2, 0, sizeof(if2));
- strncpy(if2.ifr_name, ifname, sizeof(if2.ifr_name) - 1);
+ if (sizeof(if2.ifr_name) < sizeof(ifname)) {
+ return -1;
+ }
+ strcpy(if2.ifr_name, ifname);

      if (ioctl(sock, SIOCGIFFLAGS, (char *)&if2) < 0) {
          return -1;