core: Use flexible array member if compiler has support.

* configure.ac (AC_C_FLEXIBLE_ARRAY_MEMBER): Add.
* src/engine-gpg.c (struct arg_and_data_s): Use FLEXIBLE_ARRAY_MEMBER.
(_add_arg): Use offsetof instead of sizeof.
(add_data): Likewise.

--

Before this fix, GCC 11 warns (with its bound checking feature).

Signed-off-by: NIIBE Yutaka <[email protected]>

2 files changed, 4 insertions, 3 deletions

diff --git a/configure.ac b/configure.ac
index 6cefc090..296553e3 100644
--- a/configure.ac
+++ b/configure.ac
@@ -543,6 +543,7 @@ AC_CHECK_HEADERS_ONCE([locale.h sys/select.h sys/uio.h argp.h stdint.h
 
 # Type checks.
 AC_C_INLINE
+AC_C_FLEXIBLE_ARRAY_MEMBER
 AC_CHECK_SIZEOF(unsigned int)
 AC_SYS_LARGEFILE
 AC_TYPE_OFF_T
diff --git a/src/engine-gpg.c b/src/engine-gpg.c
index b51ea173..ff037920 100644
--- a/src/engine-gpg.c
+++ b/src/engine-gpg.c
@@ -59,7 +59,7 @@ struct arg_and_data_s
   int print_fd;    /* Print the fd number and not the special form of it.  */
   int *arg_locp;   /* Write back the argv idx of this argument when
 		      building command line to this location.  */
-  char arg[1];     /* Used if data above is not used.  */
+  char arg[FLEXIBLE_ARRAY_MEMBER];     /* Used if data above is not used.  */
 };
 
 
@@ -233,7 +233,7 @@ _add_arg (engine_gpg_t gpg, const char *prefix, const char *arg, size_t arglen,
   assert (gpg);
   assert (arg);
 
-  a = malloc (sizeof *a + prefixlen + arglen);
+  a = malloc (offsetof (struct arg_and_data_s, arg) + prefixlen + arglen + 1);
   if (!a)
     return gpg_error_from_syserror ();
 
@@ -307,7 +307,7 @@ add_data (engine_gpg_t gpg, gpgme_data_t data, int dup_to, int inbound)
   assert (gpg);
   assert (data);
 
-  a = malloc (sizeof *a - 1);
+  a = malloc (offsetof (struct arg_and_data_s, arg));
   if (!a)
     return gpg_error_from_syserror ();
   a->next = NULL;