[Sema] Warn about printf %n on Android and Fuchsia

The `printf` specifier `%n` is not supported on Android's libc and will soon be removed from Fuchsia's

Reviewed By: enh

Differential Revision: https://reviews.llvm.org/D117611

1 files changed, 16 insertions, 8 deletions

diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 2765346..e2b78fa 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -499,7 +499,8 @@ public:
              1 /* null byte always written by sprintf */) {}
 
   bool HandlePrintfSpecifier(const analyze_printf::PrintfSpecifier &FS,
-                             const char *, unsigned SpecifierLen) override {
+                             const char *, unsigned SpecifierLen,
+                             const TargetInfo &) override {
 
     const size_t FieldWidth = computeFieldWidth(FS);
     const size_t Precision = computePrecision(FS);
@@ -8909,8 +8910,8 @@ public:
   void handleInvalidMaskType(StringRef MaskType) override;
 
   bool HandlePrintfSpecifier(const analyze_printf::PrintfSpecifier &FS,
-                             const char *startSpecifier,
-                             unsigned specifierLen) override;
+                             const char *startSpecifier, unsigned specifierLen,
+                             const TargetInfo &Target) override;
   bool checkFormatExpr(const analyze_printf::PrintfSpecifier &FS,
                        const char *StartSpecifier,
                        unsigned SpecifierLen,
@@ -9169,11 +9170,9 @@ bool CheckPrintfHandler::checkForCStrMembers(
   return false;
 }
 
-bool
-CheckPrintfHandler::HandlePrintfSpecifier(const analyze_printf::PrintfSpecifier
-                                            &FS,
-                                          const char *startSpecifier,
-                                          unsigned specifierLen) {
+bool CheckPrintfHandler::HandlePrintfSpecifier(
+    const analyze_printf::PrintfSpecifier &FS, const char *startSpecifier,
+    unsigned specifierLen, const TargetInfo &Target) {
   using namespace analyze_format_string;
   using namespace analyze_printf;
 
@@ -9305,6 +9304,15 @@ CheckPrintfHandler::HandlePrintfSpecifier(const analyze_printf::PrintfSpecifier
     }
   }
 
+  const llvm::Triple &Triple = Target.getTriple();
+  if (CS.getKind() == ConversionSpecifier::nArg &&
+      (Triple.isAndroid() || Triple.isOSFuchsia())) {
+    EmitFormatDiagnostic(S.PDiag(diag::warn_printf_narg_not_supported),
+                         getLocationOfByte(CS.getStart()),
+                         /*IsStringLocation*/ false,
+                         getSpecifierRange(startSpecifier, specifierLen));
+  }
+
   // Check for invalid use of field width
   if (!FS.hasValidFieldWidth()) {
     HandleInvalidAmount(FS, FS.getFieldWidth(), /* field width */ 0,