[PATCH] D102742: [IR] make stack-protector-guard-* flags into module attrs

[Nick Desaulniers via Phabricator via cfe-commits]

nickdesaulniers added inline comments.


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Comment at: clang/include/clang/Driver/Options.td:3429
   HelpText<"Use the given reg for addressing the stack-protector guard">,
-  MarshallingInfoString<CodeGenOpts<"StackProtectorGuardReg">, [{"none"}]>;
+  MarshallingInfoString<CodeGenOpts<"StackProtectorGuardReg">>;
 def mfentry : Flag<["-"], "mfentry">, HelpText<"Insert calls to fentry at function entry (x86/SystemZ only)">,
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tejohnson wrote:
> nickdesaulniers wrote:
> > tejohnson wrote:
> > > nickdesaulniers wrote:
> > > > tejohnson wrote:
> > > > > nickdesaulniers wrote:
> > > > > > tejohnson wrote:
> > > > > > > What's the effect of or reason for this change?
> > > > > > Of the 3 options added in D88631 (`mstack_protector_guard_EQ`, `mstack_protector_guard_offset_EQ`, `mstack_protector_guard_reg_EQ`) 2 are strings (`mstack_protector_guard_EQ` and `mstack_protector_guard_reg_EQ`).  It was inconsistent that one could be unspecified, where as the other could be unspecified or `"none"` (but those 2 values were equivalent).
> > > > > > 
> > > > > > Without this change, in clang/lib/CodeGen/CodeGenModule.cpp I'd need to check that `StackProtectorGuardReg != "none"` rather than `!StackProtectorGuardReg.empty()` below.
> > > > > > 
> > > > > > I can change it back, but I think the asymmetry between `mstack_protector_guard_EQ` and `mstack_protector_guard_reg_EQ` in D88631, and I missed that in code review.
> > > > > > 
> > > > > > I don't think there would be any other observers of such a change.
> > > > > I see. Does unspecified mean something like just "-mstack-protector-guard-reg=" with nothing after the =? I didn't realize that was supported.
> > > > It looks like we validate for that case in the front end already. Specifically, `RenderAnalyzerOptions` in clang/lib/Driver/ToolChains/Clang.cpp.
> > > > 
> > > >     $ clang -mstack-protector-guard-reg= ...
> > > >     clang-13: error: invalid value '' in 'mstack-protector-guard-reg='
> > > Does that mean that without the "none" handling there is no way to disable? I.e. overriding an earlier value. Not sure how important this is.
> > Oh, that's a great point.  I guess I'm not really sure of the intention of `"none"` then, @xiangzhangllvm can you comment whether that was the intention?
> > 
> > A quick test in GCC shows that GCC does not accept the value `"none"` for either `-mstack-protector-guard=` or `-mstack-protector-guard-reg=`.
> > 
> > We could strive to support disabling the command line flag once respecified, but I'd rather do it for both of the above two flags, not just `-mstack-protector-guard-reg=`.
> Yeah and it doesn't look like gcc supports anything like -mno-stack-...
> So this seems fine the way you have changed it, unless @xiangzhangllvm has a different opinion, but perhaps that could be resolved later and consistently between all the options as you note.
Sure, I'm happy to follow up on this if I got it wrong here. In the meantime, this will help our CI go back green, so I've merged it. Thank you much for the review!


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D102742/new/

https://reviews.llvm.org/D102742