[xen staging] libxl: fix -Werror=stringop-truncation in libxl__prepare_sockaddr_un

[patchbot@xxxxxxx]

commit fff1b7f50e75ad9535c86f3fcf425b4945c50a1c
Author:     Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
AuthorDate: Wed Aug 19 04:00:36 2020 +0200
Commit:     Wei Liu <wl@xxxxxxx>
CommitDate: Thu Aug 27 09:38:47 2020 +0000

    libxl: fix -Werror=stringop-truncation in libxl__prepare_sockaddr_un
    
    In file included from /usr/include/string.h:495,
                     from libxl_internal.h:38,
                     from libxl_utils.c:20:
    In function 'strncpy',
        inlined from 'libxl__prepare_sockaddr_un' at libxl_utils.c:1262:5:
    /usr/include/bits/string_fortified.h:106:10: error: '__builtin_strncpy' 
specified bound 108 equals destination size [-Werror=stringop-truncation]
      106 |   return __builtin___strncpy_chk (__dest, __src, __len, __bos 
(__dest));
          |          
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    cc1: all warnings being treated as errors
    
    Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
    Reviewed-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
---
 tools/libxl/libxl_utils.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/libxl/libxl_utils.c b/tools/libxl/libxl_utils.c
index f360f5e228..b039143b8a 100644
--- a/tools/libxl/libxl_utils.c
+++ b/tools/libxl/libxl_utils.c
@@ -1252,14 +1252,14 @@ int libxl__prepare_sockaddr_un(libxl__gc *gc,
                                struct sockaddr_un *un, const char *path,
                                const char *what)
 {
-    if (sizeof(un->sun_path) <= strlen(path)) {
+    if (sizeof(un->sun_path) - 1 <= strlen(path)) {
         LOG(ERROR, "UNIX socket path '%s' is too long for %s", path, what);
-        LOG(DEBUG, "Path must be less than %zu bytes", sizeof(un->sun_path));
+        LOG(DEBUG, "Path must be less than %zu bytes", sizeof(un->sun_path) - 
1);
         return ERROR_INVAL;
     }
     memset(un, 0, sizeof(struct sockaddr_un));
     un->sun_family = AF_UNIX;
-    strncpy(un->sun_path, path, sizeof(un->sun_path));
+    strncpy(un->sun_path, path, sizeof(un->sun_path) - 1);
     return 0;
 }
 
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