aaron.ballman added reviewers: clang-language-wg, jyknight.
aaron.ballman added a comment.
Thank you for working on this! Adding a few more reviewers for exposure.
================
Comment at: clang/include/clang/Basic/DiagnosticSemaKinds.td:6921-6926
def ext_typecheck_indirection_through_void_pointer : ExtWarn<
"ISO C++ does not allow indirection on operand of type %0">,
InGroup<DiagGroup<"void-ptr-dereference">>;
+def warn_deference_void_pointer : Warning<
+ "deference a void pointer has undefined behavior">, InGroup<
+ DiagGroup<"deference-void-pointer">>;
----------------
I think we want the extension in both C and C++
================
Comment at: clang/lib/Sema/SemaExpr.cpp:14541
+ Kind = diag::ext_typecheck_indirection_through_void_pointer;
+ else if (S.getLangOpts().C99 && !IsAfterAmp)
+ Kind = diag::warn_deference_void_pointer;
----------------
junaire wrote:
> I don't know why we don't have `getLangOpts().C89`. I'm a bit confused about
> how we deal with different C standards...
This trips up folks somewhat often, unfortunately! All of the language mode
options are cumulative, so if the user specifies C11, then C99 and C11 will
both be true. However, we don't have an explicit C89 language mode, instead we
rely on `!CPlusPlus` to tell us we're in C mode and `!C99` to tell us we're in
C89 mode. Does that make sense?
================
Comment at: clang/test/Analysis/misc-ps.m:136
if (!flag) {
- if (sizeof(*q) == 1)
+ if (sizeof(*q) == 1) // expected-warning {{deference a void pointer has
undefined behavior}}
return;
----------------
This is why I think we want to reuse the existing extension diagnostic --
there's kind of no UB in this case because the dereference is never actually
evaluated, but telling the user "this isn't allowed per spec" will at least
tell them about the portability issue.
================
Comment at: clang/test/C/drs/dr1xx.c:142
/* The behavior of all three of these is undefined. */
- (void)*p;
- (void)(i ? *p : *p);
+ (void)*p; /* expected-warning {{deference a void pointer has undefined
behavior}} */
+ (void)(i ? *p : *p); /* expected-warning {{deference a void pointer has
undefined behavior}} */
----------------
junaire wrote:
> I seem not dealing with the tests correctly, mostly because we're specifying
> multiple run lines with different standards. Can you help me a little bit
> with this? @aaron.ballman
What kind of problems are you running into?
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D134461/new/
https://reviews.llvm.org/D134461
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