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

[Ziqing Luo via cfe-commits]

================
@@ -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};
+
+  if (Ctx.getTargetInfo().getTriple().isOSDarwin())
+    return {1024};
+
+  return std::nullopt;
+}
+
+/* Follow simple references to other macros so we can match the Expr spelling */
----------------
ziqingluo-90 wrote:

nit: this function could be useful for other checks so I'd like the comment to be a bit more clear:
- We do not have to mention "match the Expr spelling" since it is unrelated to this function.
- We could make it clear that this function follows the macro chain, where all macros are "simple"---having no arguments and are defined as an identifier of another macro.  The function returns the first non-"simple" macro along the chain or nullptr if the chain is empty.

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