[PATCH] D130906: [clang] format string checking for conpile-time evaluated str literal

Timm B├Ąder via Phabricator via cfe-commits cfe-commits at lists.llvm.org
Mon Aug 1 23:33:00 PDT 2022


tbaeder added inline comments.


================
Comment at: clang/lib/Sema/SemaChecking.cpp:8507
+    if (Result.Val.isLValue()) {
+      auto *LVE = Result.Val.getLValueBase().dyn_cast<const Expr *>();
+      if (LVE && LVE->getStmtClass() == Stmt::StringLiteralClass) {
----------------
inclyc wrote:
> tbaeder wrote:
> > I think you should be able to unify the two `if` statements.
> > 
> > Can you not `dyn_cast_or_null<StringLiteral>(Result.Val.getLValueBase())` here instead of casting to `Expr*` and checking the `StmtClass`?
> `LValueBase` seems to be a wrapper of a pointer that has its own dyn_cast method.
> 
> I have changed code here like this, but it cannot compile
> ```
> auto *MaybeStringLiteral =
>         dyn_cast_or_null<StringLiteral *>(Result.Val.getLValueBase());
>     if (MaybeStringLiteral) {
>       return checkFormatStringExpr(S, MaybeStringLiteral, Args, APK, format_idx,
>                                    firstDataArg, Type, CallType,
>                                    /*InFunctionCall*/ false, CheckedVarArgs,
>                                    UncoveredArg, Offset);
>     }
> ```
> 
> ```
> <workspace>/llvm-project/llvm/include/llvm/Support/Casting.h:64:53: error: type 'clang::StringLiteral *' cannot be used prior to '::' because it has no members
>   static inline bool doit(const From &Val) { return To::classof(&Val); }
> ```
Ah, shame. This ends up calling `dyn_cast` on a `llvm::Pointerunion` as far as I can see, which seems to return `nullptr` in case the cast is unsuccessful anyway, so you could try just exploiting that: https://llvm.org/doxygen/classllvm_1_1PointerUnion.html#a9147352f78d98ee246f25d3300e0aaba


================
Comment at: clang/test/Sema/format-strings-scanf.c:235
   scanf(0 ? "%s" : "%d", i); // no warning
-  scanf(1 ? "%s" : "%d", i); // expected-warning{{format specifies type 'char *'}}
+  scanf(1 ? "%s" : "%d", i); // expected-warning{{format specifies type 'char *'}} \
+                             // expected-note{{format string is defined here}}
----------------
inclyc wrote:
> tbaeder wrote:
> > inclyc wrote:
> > > These new notes are FixIt hints, looks much better than before.
> > Can you show some sample output?
> Source:
> ```
> // sample.cpp
> #include <cstdio>
> 
> int main() {
>   int *i;
>   scanf(1 ? "%s %d" : "%d", i);
> }
> ```
> 
> previous version:
> ```
> sample.cpp:5:29: warning: format specifies type 'char *' but the argument has type 'int *' [-Wformat]
>   scanf(1 ? "%s %d" : "%d", i);
>              ~~             ^
>              %d
> sample.cpp:5:18: warning: more '%' conversions than data arguments [-Wformat-insufficient-args]
>   scanf(1 ? "%s %d" : "%d", i);
>                 ~^
> 2 warnings generated.
> ```
> 
> this patch highlights ` cond ? T : F` expressions:
> 
> ```
> sample.cpp:5:29: warning: format specifies type 'char *' but the argument has type 'int *' [-Wformat]
>   scanf(1 ? "%s %d" : "%d", i);
>         ~~~~~~~~~~~~~~~~~~  ^
> sample.cpp:5:14: note: format string is defined here
>   scanf(1 ? "%s %d" : "%d", i);
>              ^~
>              %d
> sample.cpp:5:9: warning: more '%' conversions than data arguments [-Wformat-insufficient-args]
>   scanf(1 ? "%s %d" : "%d", i);
>         ^~~~~~~~~~~~~~~~~~
> sample.cpp:5:18: note: format string is defined here
>   scanf(1 ? "%s %d" : "%d", i);
>                 ~^
> 2 warnings generated.
> ```
> 
Alright, might be a bit verbose but I agree that it is useful.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D130906/new/

https://reviews.llvm.org/D130906



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