r299774 - Sema: prevent __declspec(naked) use on x64

Aaron Ballman via cfe-commits cfe-commits at lists.llvm.org
Fri Apr 7 12:06:44 PDT 2017


On Fri, Apr 7, 2017 at 2:53 PM, Richard Smith <richard at metafoo.co.uk> wrote:
> On 7 Apr 2017 11:49 am, "David Majnemer via cfe-commits"
> <cfe-commits at lists.llvm.org> wrote:
>
>
>
> On Fri, Apr 7, 2017 at 8:30 AM, Aaron Ballman via cfe-commits
> <cfe-commits at lists.llvm.org> wrote:
>>
>> On Fri, Apr 7, 2017 at 11:13 AM, Saleem Abdulrasool via cfe-commits
>> <cfe-commits at lists.llvm.org> wrote:
>> > Author: compnerd
>> > Date: Fri Apr  7 10:13:47 2017
>> > New Revision: 299774
>> >
>> > URL: http://llvm.org/viewvc/llvm-project?rev=299774&view=rev
>> > Log:
>> > Sema: prevent __declspec(naked) use on x64
>> >
>> > MSDN (https://msdn.microsoft.com/en-us/library/h5w10wxs.aspx) indicates
>> > that `__declspec(naked)` is only permitted on x86 and ARM targets.
>> > Testing with cl does confirm this behaviour.  Provide a warning for use
>> > of `__declspec(naked)` on x64.
>>
>> Your patch is not providing a warning, it's providing an error, which
>> seems inappropriate (to me). Why is this attribute not silently
>> ignored there instead?
>
>
> FWIW, MSVC diagnoses this with an error: https://godbolt.org/g/T5sQr5
>
>
> Is there a reason we can't support this? Was our existing support broken in
> some way? We generally allow our features to be combined in arbitrary ways
> unless there's a reason not to.

For the __declspec spelling of the attribute, we shouldn't really do
*more* than what Microsoft allows, should we (even if we can)?

As for error vs warning, I was mostly pointing out that (1) the commit
comment doesn't match the behavior of the patch, which is always a
concern, and (2) most of our attributes warn rather than err, unless
there's a solid reason to err. If LLVM gets a naked attribute for a
function and the architecture doesn't support the concept, what
happens? I thought it ignored it (which suggests a warning rather than
an error, to a certain extent), but I could be wrong.

~Aaron

>
>> (Btw, I did not see a review thread for this, did I miss one?) More
>> comments below.
>>
>> >
>> > Added:
>> >     cfe/trunk/test/Sema/declspec-naked.c
>> > Modified:
>> >     cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
>> >     cfe/trunk/lib/Sema/SemaDeclAttr.cpp
>> >     cfe/trunk/test/Sema/ms-inline-asm.c
>> >
>> > Modified: cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
>> > URL:
>> > http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td?rev=299774&r1=299773&r2=299774&view=diff
>> >
>> > ==============================================================================
>> > --- cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td (original)
>> > +++ cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td Fri Apr  7
>> > 10:13:47 2017
>> > @@ -3231,7 +3231,8 @@ def err_attribute_regparm_invalid_number
>> >    "'regparm' parameter must be between 0 and %0 inclusive">;
>> >  def err_attribute_not_supported_in_lang : Error<
>> >    "%0 attribute is not supported in %select{C|C++|Objective-C}1">;
>> > -
>> > +def err_attribute_not_supported_on_arch
>> > +    : Error<"%0 attribute is not supported on '%1'">;
>> >
>> >  // Clang-Specific Attributes
>> >  def warn_attribute_iboutlet : Warning<
>> >
>> > Modified: cfe/trunk/lib/Sema/SemaDeclAttr.cpp
>> > URL:
>> > http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDeclAttr.cpp?rev=299774&r1=299773&r2=299774&view=diff
>> >
>> > ==============================================================================
>> > --- cfe/trunk/lib/Sema/SemaDeclAttr.cpp (original)
>> > +++ cfe/trunk/lib/Sema/SemaDeclAttr.cpp Fri Apr  7 10:13:47 2017
>> > @@ -1923,6 +1923,17 @@ static void handleNakedAttr(Sema &S, Dec
>> >                                                       Attr.getName()))
>> >      return;
>> >
>> > +  if (Attr.isDeclspecAttribute()) {
>> > +    const auto &Triple = S.getASTContext().getTargetInfo().getTriple();
>>
>> No need to have the Triple variable (which is a rather poor name given
>> that it's also the type name).
>> > +    const auto &Arch = Triple.getArch();
>>
>> Do not use auto for either of these.
>>
>> ~Aaron
>>
>> > +    if (Arch != llvm::Triple::x86 &&
>> > +        (Arch != llvm::Triple::arm && Arch != llvm::Triple::thumb)) {
>> > +      S.Diag(Attr.getLoc(), diag::err_attribute_not_supported_on_arch)
>> > +          << Attr.getName() << Triple.getArchName();
>> > +      return;
>> > +    }
>> > +  }
>> > +
>> >    D->addAttr(::new (S.Context) NakedAttr(Attr.getRange(), S.Context,
>> >
>> > Attr.getAttributeSpellingListIndex()));
>> >  }
>> >
>> > Added: cfe/trunk/test/Sema/declspec-naked.c
>> > URL:
>> > http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/declspec-naked.c?rev=299774&view=auto
>> >
>> > ==============================================================================
>> > --- cfe/trunk/test/Sema/declspec-naked.c (added)
>> > +++ cfe/trunk/test/Sema/declspec-naked.c Fri Apr  7 10:13:47 2017
>> > @@ -0,0 +1,11 @@
>> > +// RUN: %clang_cc1 -triple i686-unknown-windows-msvc -fsyntax-only
>> > -fdeclspec -verify %s
>> > +// RUN: %clang_cc1 -triple thumbv7-unknown-windows-msvc -fsyntax-only
>> > -fdeclspec -verify %s
>> > +// RUN: %clang_cc1 -triple x86_64-unknown-windows-msvc -fsyntax-only
>> > -fdeclspec -verify %s
>> > +#if defined(_M_IX86) || defined(_M_ARM)
>> > +// CHECK: expected-no-diagnostics
>> > +#endif
>> > +
>> > +void __declspec(naked) f(void) {}
>> > +#if !defined(_M_IX86) && !defined(_M_ARM)
>> > +// expected-error at -2{{'naked' attribute is not supported on 'x86_64'}}
>> > +#endif
>> >
>> > Modified: cfe/trunk/test/Sema/ms-inline-asm.c
>> > URL:
>> > http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/ms-inline-asm.c?rev=299774&r1=299773&r2=299774&view=diff
>> >
>> > ==============================================================================
>> > --- cfe/trunk/test/Sema/ms-inline-asm.c (original)
>> > +++ cfe/trunk/test/Sema/ms-inline-asm.c Fri Apr  7 10:13:47 2017
>> > @@ -1,5 +1,5 @@
>> >  // REQUIRES: x86-registered-target
>> > -// RUN: %clang_cc1 %s -triple x86_64-apple-darwin10 -fms-extensions
>> > -fasm-blocks -Wno-microsoft -Wunused-label -verify -fsyntax-only
>> > +// RUN: %clang_cc1 %s -triple i386-apple-darwin10 -fms-extensions
>> > -fasm-blocks -Wno-microsoft -Wunused-label -verify -fsyntax-only
>> >
>> >  void t1(void) {
>> >   __asm __asm // expected-error {{__asm used with no assembly
>> > instructions}}
>> >
>> >
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