[clang] [clang][Sema] Add bounds checking for libc poll (PR #177286)

[Oliver Hunt via cfe-commits]

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@@ -1140,6 +1143,152 @@ static bool ProcessFormatStringLiteral(const Expr *FormatExpr,
   return false;
 }
 
+static std::optional<int> getPathMaxValue(const ASTContext &Ctx) {
+  if (Ctx.getTargetInfo().getTriple().isOSGlibc())
+    return {4096};
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ojhunt wrote:

You can use PP.getMacroDefinition for PATH_MAX, giving you macro info, from there you can examine the macro definition, which will presumably be a single token that is an integer literal, which you can parse out. If PATH_MAX is not defined then you definitionally know the developer cannot be doing the correct thing so you can warn.

Rather than caching that you might choose to ask for getMacroDefinition at the location of the expression - it limits your ability to cache but as it's just a couple of hash lookups it should be completely fine.

If PATH_MAX is not a single token numeric macro you could emit a warning and someone will file a bug that allows us to see what other patterns we need to support.

https://github.com/llvm/llvm-project/pull/177286