[clang] [Clang][counted_by] Honor counted_by in __bdos on direct struct access (PR #201161)

[Kees Cook via cfe-commits]

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@@ -16276,13 +16276,44 @@ static bool determineEndOffset(EvalInfo &Info, SourceLocation ExprLoc,
   return true;
 }
 
+/// Determine whether @p E designates a flexible array member annotated with
+/// 'counted_by'. This mirrors the Expr-walking that CGBuiltin's
+/// StructFieldAccess / emitCountedByMemberSize do to decide whether to emit
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kees wrote:

Hm, on further investigation, I needed to match GCC's behavior here. I need to deliberately treat '&af.fam' (address-of-array) as *not* a `counted_by` access since '&af.fam' designates the array object as a whole and gets the layout-derived size, while 'af.fam' (decayed) and '&af.fam[idx]' designate element-pointers and get the count-based size.

I will move the visitor code out to get shared; I wasn't sure how to do that, but I think putting it in Expr.cpp/h works?


https://github.com/llvm/llvm-project/pull/201161