Re: [PATCH] restore ancient -Waddress for weak symbols [PR33925]

[Martin Sebor <msebor@gmail.com>]

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On 10/4/21 3:37 PM, Jason Merrill wrote:
> On 10/4/21 14:42, Martin Sebor wrote:
>> While resolving the recent -Waddress enhancement request (PR
>> PR102103) I came across a 2007 problem report about GCC 4 having
>> stopped warning for using the address of inline functions in
>> equality comparisons with null.  With inline functions being
>> commonplace in C++ this seems like an important use case for
>> the warning.
>>
>> The change that resulted in suppressing the warning in these
>> cases was introduced inadvertently in a fix for PR 22252.
>>
>> To restore the warning, the attached patch enhances
>> the decl_with_nonnull_addr_p() function to return true also for
>> weak symbols for which a definition has been provided.
> 
> I think you probably want to merge this function with 
> fold-const.c:maybe_nonzero_address, which already handles more cases.

maybe_nonzero_address() doesn't behave quite like
decl_with_nonnull_addr_p() expects and I'm reluctant to muck
around with the former too much since it's used for codegen,
while the latter just for warnings.  (There is even a case
where the functions don't behave the same, and would result
in different warnings between C and C++ without some extra
help.)

So in the attached revision I just have maybe_nonzero_address()
call decl_with_nonnull_addr_p() and then refine the failing
(or uncertain) cases separately, with some overlap between
them.

Since I worked on this someone complained that some instances
of the warning newly enhanced under PR102103 aren't suppresed
in code resulting from macro expansion.  Since it's trivial,
I include the fix for that report in this patch as well.

Tested on x86_64-linux.

Martin

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Restore ancient -Waddress for weak symbols [PR33925].

Resolves:
PR c/33925 - gcc -Waddress lost some useful warnings
PR c/102867 - -Waddress from macro expansion in readelf.c

gcc/c-family/ChangeLog:

	PR c++/33925
	PR c/102867
	* c-common.c (decl_with_nonnull_addr_p): Call maybe_nonzero_address
	and improve handling tof defined symbols.

gcc/c/ChangeLog:

	PR c++/33925
	PR c/102867
	* c-typeck.c (maybe_warn_for_null_address): Suppress warnings for
	code resulting from macro expansion.

gcc/cp/ChangeLog:

	PR c++/33925
	PR c/102867
	* typeck.c (warn_for_null_address): Suppress warnings for code
	resulting from macro expansion.

gcc/ChangeLog:

	PR c++/33925
	PR c/102867
	* doc/invoke.texi (-Waddress): Update.
	* fold-const.c (maybe_nonzero_address): Declare extern.  Simplify
	for readability.
	* tree.h (maybe_nonzero_address): Declare.

gcc/testsuite/ChangeLog:

	PR c++/33925
	PR c/102867
	* g++.dg/warn/Walways-true-2.C: Adjust to avoid a valid warning.
	* c-c++-common/Waddress-5.c: New test.
	* c-c++-common/Waddress-6.c: New test.
	* g++.dg/warn/Waddress-7.C: New test.
	* g++.dg/warn/Walways-true-2.C: Adjust to avoid a valid warning.
	* gcc.dg/weak/weak-3.c: Expect a warning.

diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index 32c7e3e8972..71cc74ac63d 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -3395,16 +3395,46 @@ c_wrap_maybe_const (tree expr, bool non_const)
 
 /* Return whether EXPR is a declaration whose address can never be NULL.
    The address of the first struct member could be NULL only if it were
-   accessed through a NULL pointer, and such an access would be invalid.  */
+   accessed through a NULL pointer, and such an access would be invalid.
+   The address of a weak symbol may be null unless it has a definition.  */
 
 bool
 decl_with_nonnull_addr_p (const_tree expr)
 {
-  return (DECL_P (expr)
-	  && (TREE_CODE (expr) == FIELD_DECL
-	      || TREE_CODE (expr) == PARM_DECL
-	      || TREE_CODE (expr) == LABEL_DECL
-	      || !DECL_WEAK (expr)));
+  if (maybe_nonzero_address (const_cast <tree>(expr)) > 0)
+    return true;
+
+  if (!DECL_P (expr))
+    return false;
+
+  if (TREE_CODE (expr) == FIELD_DECL
+      || TREE_CODE (expr) == PARM_DECL
+      || TREE_CODE (expr) == LABEL_DECL)
+    return true;
+
+  if (!VAR_OR_FUNCTION_DECL_P (expr))
+    return false;
+
+  if (!DECL_WEAK (expr))
+    /* Ordinary (non-weak) symbols have nonnull addresses.  */
+    return true;
+
+  if (DECL_INITIAL (expr) && DECL_INITIAL (expr) != error_mark_node)
+    /* Initialized weak symbols have nonnull addresses.  */
+    return true;
+
+  if (DECL_EXTERNAL (expr) || !TREE_STATIC (expr))
+    /* Uninitialized extern weak symbols and weak symbols with no
+       allocated stroage might have a null address.  */
+    return false;
+
+  tree attribs = DECL_ATTRIBUTES (expr);
+  if (lookup_attribute ("weakref", attribs))
+    /* Weakref symbols might have a null address unless their referent
+       is known not to.  Don't bother following weakref targets here.  */
+    return false;
+
+  return true;
 }
 
 /* Prepare expr to be an argument of a TRUTH_NOT_EXPR,
diff --git a/gcc/c/c-typeck.c b/gcc/c/c-typeck.c
index 0aac978c02e..0ceedfa7b04 100644
--- a/gcc/c/c-typeck.c
+++ b/gcc/c/c-typeck.c
@@ -11571,7 +11571,10 @@ build_vec_cmp (tree_code code, tree type,
 static void
 maybe_warn_for_null_address (location_t loc, tree op, tree_code code)
 {
-  if (!warn_address || warning_suppressed_p (op, OPT_Waddress))
+  /* Prevent warnings issued for macro expansion.  */
+  if (!warn_address
+      || warning_suppressed_p (op, OPT_Waddress)
+      || from_macro_expansion_at (loc))
     return;
 
   if (TREE_CODE (op) == NOP_EXPR)
diff --git a/gcc/cp/typeck.c b/gcc/cp/typeck.c
index ab0f9da2552..ae40e27e1d5 100644
--- a/gcc/cp/typeck.c
+++ b/gcc/cp/typeck.c
@@ -4597,9 +4597,11 @@ build_vec_cmp (tree_code code, tree type,
 static void
 warn_for_null_address (location_t location, tree op, tsubst_flags_t complain)
 {
+  /* Prevent warnings issued for macro expansion.  */
   if (!warn_address
       || (complain & tf_warning) == 0
       || c_inhibit_evaluation_warnings != 0
+      || from_macro_expansion_at (location)
       || warning_suppressed_p (op, OPT_Waddress))
     return;
 
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 71992b8c597..99dfce7201a 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -8603,6 +8603,8 @@ suppressed by casting the pointer operand to an integer type such
 as @code{inptr_t} or @code{uinptr_t}.
 Comparisons against string literals result in unspecified behavior
 and are not portable, and suggest the intent was to call @code{strcmp}.
+The warning is suppressed if the suspicious expression is the result
+of macro expansion.
 @option{-Waddress} warning is enabled by @option{-Wall}.
 
 @item -Wno-address-of-packed-member
diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index ff23f12f33c..4a173d278fb 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -9900,18 +9900,20 @@ pointer_may_wrap_p (tree base, tree offset, poly_int64 bitpos)
    symbol), and a negative integer when the symbol is not yet in the
    symbol table and so whether or not its address is zero is unknown.
    For function local objects always return positive integer.  */
-static int
+int
 maybe_nonzero_address (tree decl)
 {
-  if (DECL_P (decl) && decl_in_symtab_p (decl))
+  if (!DECL_P (decl))
+    return -1;
+
+  if (decl_in_symtab_p (decl))
     if (struct symtab_node *symbol = symtab_node::get_create (decl))
       return symbol->nonzero_address ();
 
   /* Function local objects are never NULL.  */
-  if (DECL_P (decl)
-      && (DECL_CONTEXT (decl)
+  if (DECL_CONTEXT (decl)
       && TREE_CODE (DECL_CONTEXT (decl)) == FUNCTION_DECL
-      && auto_var_in_fn_p (decl, DECL_CONTEXT (decl))))
+      && auto_var_in_fn_p (decl, DECL_CONTEXT (decl)))
     return 1;
 
   return -1;
diff --git a/gcc/testsuite/c-c++-common/Waddress-5.c b/gcc/testsuite/c-c++-common/Waddress-5.c
new file mode 100644
index 00000000000..5d63c7dae7c
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Waddress-5.c
@@ -0,0 +1,133 @@
+/* PR c/33925 - missing -Waddress with the address of an inline function
+   { dg-do compile }
+   { dg-options "-Wall" }
+   { dg-require-weak "" } */
+
+extern inline int eifn (void);
+extern inline int eifn_def (void) { return 0; }
+
+static inline int sifn (void);
+static inline int sifn_def (void) { return 0; }
+
+inline int ifn (void);
+inline int ifn_def (void) { return 0; }
+
+extern __attribute__ ((weak)) int ewfn (void);
+extern __attribute__ ((weak)) int ewfn_def (void) { return 0;  }
+
+__attribute__ ((weak)) int wfn (void);
+__attribute__ ((weak)) int wfn_def (void) { return 0; }
+
+static __attribute__((weakref ("ewfn"))) int swrfn (void);
+
+void test_function_eqz (int *p)
+{
+  *p++ = eifn == 0;                     // { dg-warning "-Waddress" }
+  *p++ = eifn_def == 0;                 // { dg-warning "-Waddress" }
+  *p++ = sifn == 0;                     // { dg-warning "-Waddress" }
+  *p++ = sifn_def == 0;                 // { dg-warning "-Waddress" }
+  *p++ = ifn == 0;                      // { dg-warning "-Waddress" }
+  *p++ = ifn_def == 0;                  // { dg-warning "-Waddress" }
+  *p++ = ewfn == 0;
+  *p++ = ewfn_def == 0;                 // { dg-warning "-Waddress" }
+  *p++ = wfn == 0;
+  *p++ = wfn_def == 0;                  // { dg-warning "-Waddress" }
+  *p++ = swrfn == 0;
+}
+
+
+int test_function_if (int i)
+{
+  if (eifn)                             // { dg-warning "-Waddress" }
+    i++;
+  if (eifn_def)                         // { dg-warning "-Waddress" }
+    i++;
+  if (sifn)                             // { dg-warning "-Waddress" }
+    i++;
+  if (sifn_def)                         // { dg-warning "-Waddress" }
+    i++;
+  if (ifn)                              // { dg-warning "-Waddress" }
+    i++;
+  if (ifn_def)                          // { dg-warning "-Waddress" }
+    i++;
+  if (ewfn)
+    i++;
+  if (ewfn_def)                         // { dg-warning "-Waddress" }
+    i++;
+  if (wfn)
+    i++;
+  if(wfn_def)                           // { dg-warning "-Waddress" }
+    i++;
+  if (swrfn)
+    i++;
+  return i;
+}
+
+
+extern int ei;
+extern int ei_def = 1;
+
+static int si;
+static int si_def = 1;
+
+int i;
+int i_def = 1;
+
+extern __attribute__ ((weak)) int ewi;   // declaration (may be null)
+extern __attribute__ ((weak)) int ewi_def = 1;
+
+__attribute__ ((weak)) int wi;          // definition (cannot be bull)
+__attribute__ ((weak)) int wi_def = 1;
+
+static __attribute__((weakref ("ewi"))) int swri;
+
+void test_scalar (int *p)
+{
+  *p++ = &ei == 0;                      // { dg-warning "-Waddress" }
+  *p++ = &ei_def == 0;                  // { dg-warning "-Waddress" }
+  *p++ = &si == 0;                      // { dg-warning "-Waddress" }
+  *p++ = &si_def == 0;                  // { dg-warning "-Waddress" }
+  *p++ = &i == 0;                       // { dg-warning "-Waddress" }
+  *p++ = &i_def == 0;                   // { dg-warning "-Waddress" }
+  *p++ = &ewi == 0;
+  *p++ = &ewi_def == 0;                 // { dg-warning "-Waddress" }
+  *p++ = &wi == 0;                      // { dg-warning "-Waddress" }
+  *p++ = &wi_def == 0;                  // { dg-warning "-Waddress" }
+  *p++ = &swri == 0;
+}
+
+
+extern int eia[];
+extern int eia_def[] = { 1 };
+
+static int sia[1];
+static int sia_def[1] = { 1 };
+
+int ia[1];
+int ia_def[] = { 1 };
+
+extern __attribute__ ((weak)) int ewia[];
+extern __attribute__ ((weak)) int ewia_def[] = { 1 };
+
+__attribute__ ((weak)) int wia[1];      // definition (cannot be null)
+__attribute__ ((weak)) int wia_def[] = { 1 };
+
+static __attribute__((weakref ("ewia"))) int swria[1];
+
+void test_array (int *p)
+{
+  *p++ = eia == 0;                      // { dg-warning "-Waddress" }
+  *p++ = eia_def == 0;                  // { dg-warning "-Waddress" }
+  *p++ = sia == 0;                      // { dg-warning "-Waddress" }
+  *p++ = sia_def == 0;                  // { dg-warning "-Waddress" }
+  *p++ = ia == 0;                       // { dg-warning "-Waddress" }
+  *p++ = ia_def == 0;                   // { dg-warning "-Waddress" }
+  *p++ = ewia == 0;
+  *p++ = ewia_def == 0;                 // { dg-warning "-Waddress" }
+  *p++ = wia == 0;                      // { dg-warning "-Waddress" }
+  *p++ = wia_def == 0;                  // { dg-warning "-Waddress" }
+  *p++ = swria == 0;
+}
+
+/* { dg-prune-output "never defined" }
+   { dg-prune-output "initialized and declared 'extern'" } */
diff --git a/gcc/testsuite/c-c++-common/Waddress-6.c b/gcc/testsuite/c-c++-common/Waddress-6.c
new file mode 100644
index 00000000000..e66e6e4a0b0
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Waddress-6.c
@@ -0,0 +1,32 @@
+/* PR c/102867 - -Waddress from macro expansion in readelf.c
+   { dg-do compile }
+   { dg-options "-Wall" } */
+
+#define F(x) ((&x) != 0)
+
+int warn_nomacro (int *p, int i)
+{
+  return &p[i] != 0;          // { dg-warning "-Waddress" }
+}
+
+int nowarn_macro_expansion (int *p, int i)
+{
+  // Verify that -Waddress isn't issued for code from macro expansion.
+  return F (p[i]);            // { dg-bogus "-Waddress" }
+}
+
+#define G(x, i) ((&x) + i)
+
+int warn_function_macro_expansion (int *p, int i)
+{
+  /* Verify that -Waddress is issued for code involving macro expansion
+     where the comparison takes place outside the macro.  */
+  return G (*p, i) != 0;      // { dg-warning "-Waddress" }
+}
+
+#define malloc __builtin_malloc
+
+int warn_object_macro_expansion (int *p, int i)
+{
+  return malloc != 0;         // { dg-warning "-Waddress" }
+}
diff --git a/gcc/testsuite/g++.dg/warn/Waddress-7.C b/gcc/testsuite/g++.dg/warn/Waddress-7.C
new file mode 100644
index 00000000000..efdafa50cd1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Waddress-7.C
@@ -0,0 +1,76 @@
+/* PR c/33925 - missing -Waddress with the address of an inline function
+   { dg-do compile }
+   { dg-options "-Wall" } */
+
+struct A
+{
+  int mf ();
+  int mf_def () { return 0; }
+
+  static int smf ();
+  static int smf_def () { return 0; }
+
+  int mi;
+  static int smi;
+  static int smi_def;
+
+  __attribute__ ((weak)) static int wsmi;
+  __attribute__ ((weak)) static int wsmi_def;
+
+  int mia[];
+  static int smia[];
+  static int smia_def[];
+
+  __attribute__ ((weak)) static int wsmia[];
+  __attribute__ ((weak)) static int wsmia_def[];
+
+  void test_waddress (bool*);
+};
+
+
+/* __attribute__ ((weak)) static */ int A::smi_def = 0;
+/* __attribute__ ((weak)) static */ int A::smia_def[] = { 0 };
+
+/* __attribute__ ((weak)) static */ int A::wsmi_def = 0;
+/* __attribute__ ((weak)) static */ int A::wsmia_def[] = { 0 };
+
+
+
+void A::test_waddress (bool *p)
+{
+  if (mf)                               // { dg-error "cannot convert" }
+    p++;
+  if (mf_def)                           // { dg-error "cannot convert" }
+    p++;
+
+  if (smf)                              // { dg-warning "-Waddress" }
+    p++;
+  if (smf_def)                          // { dg-warning "-Waddress" }
+    p++;
+
+  if (&mi)                              // { dg-warning "-Waddress" }
+    p++;
+  if (&smi)                             // { dg-warning "-Waddress" }
+    p++;
+  if (&smi_def)                         // { dg-warning "-Waddress" }
+    p++;
+
+  if (&wsmi)
+    p++;
+
+  if (&wsmi_def)                        // { dg-warning "-Waddress" }
+    p++;
+
+  if (mia)                              // { dg-warning "-Waddress" }
+    p++;
+  if (smia)                             // { dg-warning "-Waddress" }
+    p++;
+  if (smia_def)                         // { dg-warning "-Waddress" }
+    p++;
+
+  if (wsmia)
+    p++;
+
+  if (wsmia_def)                        // { dg-warning "-Waddress" }
+    p++;
+}
diff --git a/gcc/testsuite/g++.dg/warn/Walways-true-2.C b/gcc/testsuite/g++.dg/warn/Walways-true-2.C
index 29a80e5c113..e951e95b336 100644
--- a/gcc/testsuite/g++.dg/warn/Walways-true-2.C
+++ b/gcc/testsuite/g++.dg/warn/Walways-true-2.C
@@ -9,7 +9,7 @@
 
 extern int foo (int) __attribute__ ((weak));
 
-int i __attribute__ ((weak));
+extern int i __attribute__ ((weak));
 
 void
 bar (int a)
diff --git a/gcc/testsuite/gcc.dg/Walways-true-2.c b/gcc/testsuite/gcc.dg/Walways-true-2.c
index 7f0bb7b10b9..ae3262b6876 100644
--- a/gcc/testsuite/gcc.dg/Walways-true-2.c
+++ b/gcc/testsuite/gcc.dg/Walways-true-2.c
@@ -9,7 +9,7 @@
 
 extern int foo (int) __attribute__ ((weak));
 
-int i __attribute__ ((weak));
+extern int i __attribute__ ((weak));
 
 void
 bar (int a)
diff --git a/gcc/testsuite/gcc.dg/weak/weak-3.c b/gcc/testsuite/gcc.dg/weak/weak-3.c
index a719848c935..ac85f42b34d 100644
--- a/gcc/testsuite/gcc.dg/weak/weak-3.c
+++ b/gcc/testsuite/gcc.dg/weak/weak-3.c
@@ -68,7 +68,9 @@ void * ffoox1g (void) { return (void *)0; }
 extern void * ffoo1g (void)  __attribute__((weak, alias ("ffoox1g")));
 void * foo1g (void)
 {
-  if (ffoo1g)
+  /* ffoo1g is a weak alias for a symbol defined in this file, expect
+     a -Waddress for the test (which is folded to true).  */
+  if (ffoo1g)       // { dg-warning "-Waddress" }
     ffoo1g ();
   return 0;
 }