nickdesaulniers added inline comments.
================
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)">,
----------------
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=`.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D102742/new/
https://reviews.llvm.org/D102742
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