r255371 - Error on redeclaring with a conflicting asm label and on redeclaring with an asm label after the first ODR-use. Detects problems like the one in PR22830 where gcc and clang both compiled the file but with different behaviour.

[Kostya Serebryany via cfe-commits]

I am now observing this error message when building glibc with clang (from
trunk):
../include/string.h:101:28: error: cannot apply asm label to function after
its first use
libc_hidden_builtin_proto (memcpy)
(many more instances)


Do you think this is a bug in glibc code, or the error message could be
more relaxed?





On Fri, Dec 11, 2015 at 1:28 PM, Nick Lewycky via cfe-commits <
cfe-commits at lists.llvm.org> wrote:

> Author: nicholas
> Date: Fri Dec 11 15:28:55 2015
> New Revision: 255371
>
> URL: http://llvm.org/viewvc/llvm-project?rev=255371&view=rev
> Log:
> Error on redeclaring with a conflicting asm label and on redeclaring with
> an asm label after the first ODR-use. Detects problems like the one in
> PR22830 where gcc and clang both compiled the file but with different
> behaviour.
>
> Added:
>     cfe/trunk/test/Sema/asm-label.c
> Modified:
>     cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
>     cfe/trunk/lib/Sema/SemaDecl.cpp
>
> Modified: cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
> URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td?rev=255371&r1=255370&r2=255371&view=diff
>
> ==============================================================================
> --- cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td (original)
> +++ cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td Fri Dec 11
> 15:28:55 2015
> @@ -4259,6 +4259,9 @@ def err_tag_definition_of_typedef : Erro
>  def err_conflicting_types : Error<"conflicting types for %0">;
>  def err_different_pass_object_size_params : Error<
>    "conflicting pass_object_size attributes on parameters">;
> +def err_late_asm_label_name : Error<
> +  "cannot apply asm label to %select{variable|function}0 after its first
> use">;
> +def err_different_asm_label : Error<"conflicting asm label">;
>  def err_nested_redefinition : Error<"nested redefinition of %0">;
>  def err_use_with_wrong_tag : Error<
>    "use of %0 with tag type that does not match previous declaration">;
>
> Modified: cfe/trunk/lib/Sema/SemaDecl.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDecl.cpp?rev=255371&r1=255370&r2=255371&view=diff
>
> ==============================================================================
> --- cfe/trunk/lib/Sema/SemaDecl.cpp (original)
> +++ cfe/trunk/lib/Sema/SemaDecl.cpp Fri Dec 11 15:28:55 2015
> @@ -2379,9 +2379,24 @@ void Sema::mergeDeclAttributes(NamedDecl
>    if (!Old->hasAttrs() && !New->hasAttrs())
>      return;
>
> -  // attributes declared post-definition are currently ignored
> +  // Attributes declared post-definition are currently ignored.
>    checkNewAttributesAfterDef(*this, New, Old);
>
> +  if (AsmLabelAttr *NewA = New->getAttr<AsmLabelAttr>()) {
> +    if (AsmLabelAttr *OldA = Old->getAttr<AsmLabelAttr>()) {
> +      if (OldA->getLabel() != NewA->getLabel()) {
> +        // This redeclaration changes __asm__ label.
> +        Diag(New->getLocation(), diag::err_different_asm_label);
> +        Diag(OldA->getLocation(), diag::note_previous_declaration);
> +      }
> +    } else if (Old->isUsed()) {
> +      // This redeclaration adds an __asm__ label to a declaration that
> has
> +      // already been ODR-used.
> +      Diag(New->getLocation(), diag::err_late_asm_label_name)
> +        << isa<FunctionDecl>(Old) <<
> New->getAttr<AsmLabelAttr>()->getRange();
> +    }
> +  }
> +
>    if (!Old->hasAttrs())
>      return;
>
>
> Added: cfe/trunk/test/Sema/asm-label.c
> URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/asm-label.c?rev=255371&view=auto
>
> ==============================================================================
> --- cfe/trunk/test/Sema/asm-label.c (added)
> +++ cfe/trunk/test/Sema/asm-label.c Fri Dec 11 15:28:55 2015
> @@ -0,0 +1,30 @@
> +// RUN: %clang_cc1 -verify %s
> +
> +void f();
> +void f() __asm__("fish");
> +void g();
> +
> +void f() {
> +  g();
> +}
> +void g() __asm__("gold");  // expected-error{{cannot apply asm label to
> function after its first use}}
> +
> +void h() __asm__("hose");  // expected-note{{previous declaration is
> here}}
> +void h() __asm__("hair");  // expected-error{{conflicting asm label}}
> +
> +int x;
> +int x __asm__("xenon");
> +int y;
> +
> +int test() { return y; }
> +
> +int y __asm__("yacht");  // expected-error{{cannot apply asm label to
> variable after its first use}}
> +
> +int z __asm__("zebra");  // expected-note{{previous declaration is here}}
> +int z __asm__("zooms");  // expected-error{{conflicting asm label}}
> +
> +
> +// No diagnostics on the following.
> +void __real_readlink() __asm("readlink");
> +void readlink() __asm("__protected_readlink");
> +void readlink() { __real_readlink(); }
>
>
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