[PATCH] D148381: [WIP][Clang] Add element_count attribute

[Nick Desaulniers via Phabricator via cfe-commits]

nickdesaulniers added inline comments.


================
Comment at: clang/lib/CodeGen/CGExpr.cpp:951-952
+    if (auto *ME = dyn_cast<MemberExpr>(CE->getSubExpr())) {
+      if (ME->isFlexibleArrayMemberLike(CGF.getContext(),
+                                        StrictFlexArraysLevel, true)) {
+        if (auto *MD = dyn_cast<FieldDecl>(ME->getMemberDecl())) {
----------------
void wrote:
> nickdesaulniers wrote:
> > eventually, we may want to support non-FAMs:
> > 
> > ```
> > struct foo {
> >   size_t count;
> >   char arr [PATH_MAX] __attribute((element_count("count")));
> > };
> > 
> > char *foo (size_t offset) {
> >   struct foo my_foo = {
> >     .count = sizeof("hello"),
> >     .arr = "hello",
> >   };
> >   return &my_foo.arr[offset];
> > }
> > ```
> Maybe? Though this attribute is really only for the sanitizer, which could all ready use `PATH_MAX` to ensure that it doesn't overrun the array.
Note that `my_foo.arr` is not fully initialized; a value > sizeof("hello") and < PATH_MAX will access uninitialized memory. I think this pattern is very common in C code (use excessive stack allocation partially initialized rather than heap).


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D148381/new/

https://reviews.llvm.org/D148381