PR c/77336 - -Wsuggest-attribute=format warning overly simplistic

gcc/c-family/ChangeLog:

	PR c/77336
	* c-format.c (check_function_format): Avoid issuing warnings for
	functions unless they call format functions with non-constant
	format strings.

gcc/testsuite/ChangeLog:

	PR c/77336
	* gcc.dg/format/miss-7.c: New test.

From-SVN: r240013

diff --git a/gcc/c-family/ChangeLog b/gcc/c-family/ChangeLog
index 9d9344ffa9f20ebca2f49d52e42848154fcaa139..5d642d71ecee9c20deb4bf164188930c5f74891a 100644 (file)
--- a/gcc/c-family/ChangeLog
+++ b/gcc/c-family/ChangeLog
@@ -1,3 +1,10 @@
+2016-09-06 Martin Sebor  <msebor@redhat.com>
+
+       PR c/77336
+       * c-format.c (check_function_format): Avoid issuing warnings for
+       functions unless they call format functions with non-constant
+       format strings.
+
 2016-09-06  Richard Biener  <rguenther@suse.de>
 
        PR c/77450

diff --git a/gcc/c-family/c-format.c b/gcc/c-family/c-format.c
index ad434f810ceebf2743e6f35183ed875b8264a756..413962eec21086d9eb0b719360124baa87a8512a 100644 (file)
--- a/gcc/c-family/c-format.c
+++ b/gcc/c-family/c-format.c
@@ -31,6 +31,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "c-format.h"
 #include "diagnostic.h"
 #include "selftest.h"
+#include "builtins.h"
 
 /* Handle attributes associated with format checking.  */
 
@@ -1212,9 +1213,17 @@ check_function_format (tree attrs, int nargs, tree *argarray)
                params = tree_cons (NULL_TREE, argarray[i], params);
              check_format_info (&info, params);
            }
+
+         /* Attempt to detect whether the current function might benefit
+            from the format attribute if the called function is decorated
+            with it.  Avoid using calls with string literal formats for
+            guidance since those are unlikely to be viable candidates.  */
          if (warn_suggest_attribute_format && info.first_arg_num == 0
              && (format_types[info.format_type].flags
-                 & (int) FMT_FLAG_ARG_CONVERT))
+                 & (int) FMT_FLAG_ARG_CONVERT)
+             /* c_strlen will fail for a function parameter but succeed
+                for a literal or constant array.  */
+             && !c_strlen (argarray[info.format_num - 1], 1))
            {
              tree c;
              for (c = TYPE_ATTRIBUTES (TREE_TYPE (current_function_decl));
@@ -1242,8 +1251,9 @@ check_function_format (tree attrs, int nargs, tree *argarray)
                        break;
                    }
                  if (args != 0)
-                   warning (OPT_Wsuggest_attribute_format, "function might "
-                            "be possible candidate for %qs format attribute",
+                   warning (OPT_Wsuggest_attribute_format, "function %qD "
+                            "might be a candidate for %qs format attribute",
+                            current_function_decl,
                             format_types[info.format_type].name);
                }
            }

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index acb0e201b5b5597fc143fc5b22381e7a8dca8ba1..4e24658c99384033a4f6adc9cafa8e19557bb130 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2016-09-06 Martin Sebor  <msebor@redhat.com>
+
+       PR c/77336
+       * gcc.dg/format/miss-7.c: New test.
+
 2016-09-06  Uros Bizjak  <ubizjak@gmail.com>
 
        * gfortran.dg/c_by_val_1.f: Correct the call to c_to_c and c_to_c8.

diff --git a/gcc/testsuite/gcc.dg/format/miss-7.c b/gcc/testsuite/gcc.dg/format/miss-7.c
new file mode 100644 (file)
index 0000000..828b781
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/format/miss-7.c
@@ -0,0 +1,36 @@
+/* PR77336 - -Wsuggest-attribute=format warning overly simplistic */
+/* { dg-do compile } */
+/* { dg-options "-Wsuggest-attribute=format" } */
+
+#include "format.h"
+
+const char format[] = "%i";
+
+void foo (char *d, unsigned n, va_list va)
+{
+  (void)&n;
+
+  /* The following calls don't imply that the enclosing function is
+     a candiate for the format attribute because it uses a string
+     constant as the format.  */
+  vsnprintf (d, n, "%i", va);
+
+  vsnprintf (d, n, format, va);
+
+  /* In theory this should not trigger the warning either but GCC
+     doesn't treat the local static constant the same way as the
+     global and issues a false positive.
+  const char fmt[] = "%i";
+  vsnprintf (d, n, fmt, va);
+  */
+}
+
+void bar (char *d, unsigned n, const char *f, va_list va)
+{
+  (void)&n;
+
+  /* The following call suggests that the enclosing function might
+     be a candiate for the format attribute because it doesn't use
+     a string literal as the format.  */
+  vsnprintf (d, n, f, va);   /* { dg-warning "function .bar. might be a candidate for .gnu_printf. format attribute" } */
+}