[clang][Sema] Accept gnu format attributes (#160255)

This patch teaches clang accepts gnu_printf, gnu_scanf, gnu_strftime and
gnu_strfmon. These attributes are aliases for printf, scanf, strftime and
strfmon.

Ref: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html
Fixes: #16219

---------

Co-authored-by: Sirraide <aeternalmail@gmail.com>

Author: higuoxing

clang/docs/ReleaseNotes.rst

@@ -272,6 +272,9 @@ Attribute Changes in Clang
   attribute, allowing the attribute to only be attached to the declaration. Prior, this would be
   treated as an error where the definition and declaration would have differing types.
 
+- New format attributes ``gnu_printf``, ``gnu_scanf``, ``gnu_strftime`` and ``gnu_strfmon`` are added
+  as aliases for ``printf``, ``scanf``, ``strftime`` and ``strfmon``. (#GH16219)
+
 Improvements to Clang's diagnostics
 -----------------------------------
 - Added a separate diagnostic group ``-Wfunction-effect-redeclarations``, for the more pedantic

clang/include/clang/Sema/Sema.h

@@ -503,7 +503,6 @@ enum class FormatStringType {
   FreeBSDKPrintf,
   OSTrace,
   OSLog,
-  Syslog,
   Unknown
 };
 

clang/lib/Sema/SemaChecking.cpp

@@ -6866,11 +6866,12 @@ StringRef Sema::GetFormatStringTypeName(FormatStringType FST) {
 
 FormatStringType Sema::GetFormatStringType(StringRef Flavor) {
   return llvm::StringSwitch<FormatStringType>(Flavor)
-      .Case("scanf", FormatStringType::Scanf)
-      .Cases("printf", "printf0", "syslog", FormatStringType::Printf)
+      .Cases("gnu_scanf", "scanf", FormatStringType::Scanf)
+      .Cases("gnu_printf", "printf", "printf0", "syslog",
+             FormatStringType::Printf)
       .Cases("NSString", "CFString", FormatStringType::NSString)
-      .Case("strftime", FormatStringType::Strftime)
-      .Case("strfmon", FormatStringType::Strfmon)
+      .Cases("gnu_strftime", "strftime", FormatStringType::Strftime)
+      .Cases("gnu_strfmon", "strfmon", FormatStringType::Strfmon)
       .Cases("kprintf", "cmn_err", "vcmn_err", "zcmn_err",
              FormatStringType::Kprintf)
       .Case("freebsd_kprintf", FormatStringType::FreeBSDKPrintf)
@@ -6990,7 +6991,6 @@ bool Sema::CheckFormatArguments(ArrayRef<const Expr *> Args,
     case FormatStringType::Kprintf:
     case FormatStringType::FreeBSDKPrintf:
     case FormatStringType::Printf:
-    case FormatStringType::Syslog:
       Diag(FormatLoc, diag::note_format_security_fixit)
         << FixItHint::CreateInsertion(FormatLoc, "\"%s\", ");
       break;
@@ -9120,8 +9120,7 @@ static void CheckFormatString(
   if (Type == FormatStringType::Printf || Type == FormatStringType::NSString ||
       Type == FormatStringType::Kprintf ||
       Type == FormatStringType::FreeBSDKPrintf ||
-      Type == FormatStringType::OSLog || Type == FormatStringType::OSTrace ||
-      Type == FormatStringType::Syslog) {
+      Type == FormatStringType::OSLog || Type == FormatStringType::OSTrace) {
     bool IsObjC =
         Type == FormatStringType::NSString || Type == FormatStringType::OSTrace;
     if (ReferenceFormatString == nullptr) {
@@ -9157,8 +9156,7 @@ bool Sema::CheckFormatStringsCompatible(
   if (Type != FormatStringType::Printf && Type != FormatStringType::NSString &&
       Type != FormatStringType::Kprintf &&
       Type != FormatStringType::FreeBSDKPrintf &&
-      Type != FormatStringType::OSLog && Type != FormatStringType::OSTrace &&
-      Type != FormatStringType::Syslog)
+      Type != FormatStringType::OSLog && Type != FormatStringType::OSTrace)
     return true;
 
   bool IsObjC =
@@ -9192,8 +9190,7 @@ bool Sema::ValidateFormatString(FormatStringType Type,
   if (Type != FormatStringType::Printf && Type != FormatStringType::NSString &&
       Type != FormatStringType::Kprintf &&
       Type != FormatStringType::FreeBSDKPrintf &&
-      Type != FormatStringType::OSLog && Type != FormatStringType::OSTrace &&
-      Type != FormatStringType::Syslog)
+      Type != FormatStringType::OSLog && Type != FormatStringType::OSTrace)
     return true;
 
   FormatStringLiteral RefLit = Str;

clang/lib/Sema/SemaDeclAttr.cpp

@@ -3629,10 +3629,11 @@ static FormatAttrKind getFormatAttrKind(StringRef Format) {
       // Check for formats that get handled specially.
       .Case("NSString", NSStringFormat)
       .Case("CFString", CFStringFormat)
-      .Case("strftime", StrftimeFormat)
+      .Cases("gnu_strftime", "strftime", StrftimeFormat)
 
       // Otherwise, check for supported formats.
-      .Cases("scanf", "printf", "printf0", "strfmon", SupportedFormat)
+      .Cases("gnu_scanf", "scanf", "gnu_printf", "printf", "printf0",
+             "gnu_strfmon", "strfmon", SupportedFormat)
       .Cases("cmn_err", "vcmn_err", "zcmn_err", SupportedFormat)
       .Cases("kprintf", "syslog", SupportedFormat) // OpenBSD.
       .Case("freebsd_kprintf", SupportedFormat)    // FreeBSD.

clang/test/Sema/attr-format.c

@@ -106,3 +106,11 @@ void b2(const char *a, ...) __attribute__((format(syslog, 1, 1)));    // expecte
 void c2(const char *a, ...) __attribute__((format(syslog, 0, 2)));    // expected-error {{'format' attribute parameter 2 is out of bounds}}
 void d2(const char *a, int c) __attribute__((format(syslog, 1, 2)));  // expected-warning {{GCC requires a function with the 'format' attribute to be variadic}}
 void e2(char *str, int c, ...) __attribute__((format(syslog, 2, 3))); // expected-error {{format argument not a string type}}
+
+// gnu_printf
+// same as format(printf(...))...
+void a2(const char *a, ...) __attribute__((format(gnu_printf, 1, 2)));    // no-error
+void b2(const char *a, ...) __attribute__((format(gnu_printf, 1, 1)));    // expected-error {{'format' attribute parameter 3 is out of bounds}}
+void c2(const char *a, ...) __attribute__((format(gnu_printf, 0, 2)));    // expected-error {{'format' attribute parameter 2 is out of bounds}}
+void d2(const char *a, int c) __attribute__((format(gnu_printf, 1, 2)));  // expected-warning {{GCC requires a function with the 'format' attribute to be variadic}}
+void e2(char *str, int c, ...) __attribute__((format(gnu_printf, 2, 3))); // expected-error {{format argument not a string type}}

clang/test/Sema/format-strings-scanf.c

@@ -30,6 +30,7 @@ int fscanf(FILE * restrict, const char * restrict, ...) ;
 int scanf(const char * restrict, ...) ;
 int sscanf(const char * restrict, const char * restrict, ...) ;
 int my_scanf(const char * restrict, ...) __attribute__((__format__(__scanf__, 1, 2)));
+int my_gnu_scanf(const char * restrict, ...) __attribute__((__format__(gnu_scanf, 1, 2)));
 
 int vscanf(const char * restrict, va_list);
 int vfscanf(FILE * restrict, const char * restrict, va_list);
@@ -98,6 +99,7 @@ void test_variants(int *i, const char *s, ...) {
   fscanf(f, "%ld", i); // expected-warning{{format specifies type 'long *' but the argument has type 'int *'}}
   sscanf(buf, "%ld", i); // expected-warning{{format specifies type 'long *' but the argument has type 'int *'}}
   my_scanf("%ld", i); // expected-warning{{format specifies type 'long *' but the argument has type 'int *'}}
+  my_gnu_scanf("%ld", i); // expected-warning{{format specifies type 'long *' but the argument has type 'int *'}}
 
   va_list ap;
   va_start(ap, s);

clang/test/Sema/format-strings.c

@@ -678,15 +678,21 @@ void pr18905(void) {
 }
 
 void __attribute__((format(strfmon,1,2))) monformat(const char *fmt, ...);
+void __attribute__((format(gnu_strfmon,1,2))) gnu_monformat(const char *fmt, ...);
 void __attribute__((format(strftime,1,0))) dateformat(const char *fmt);
+void __attribute__((format(gnu_strftime,1,0))) gnu_dateformat(const char *fmt);
 
 // Other formats
 void test_other_formats(void) {
   char *str = "";
   monformat("", 1); // expected-warning{{format string is empty}}
   monformat(str); // expected-warning{{format string is not a string literal (potentially insecure)}}
+  gnu_monformat("", 1); // expected-warning{{format string is empty}}
+  gnu_monformat(str); // expected-warning{{format string is not a string literal (potentially insecure)}}
   dateformat(""); // expected-warning{{format string is empty}}
   dateformat(str); // no-warning (using strftime non-literal is not unsafe)
+  gnu_dateformat(""); // expected-warning{{format string is empty}}
+  gnu_dateformat(str); // no-warning (using strftime non-literal is not unsafe)
 }
 
 // Do not warn about unused arguments coming from system headers.