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.
Roland McGrath via cfe-commits
cfe-commits at lists.llvm.org
Mon Jan 4 16:04:45 PST 2016
Kostya, do you remember the exact original case in glibc for 22830 and
what glibc change fixed it?
I vaguely recall the case, but not enough to find the actual change
and compare it to the new scenarios.
I suspect that the original case was easy to fix because it was just
that the hidden_proto magic had been put in the wrong place.
The fstat/__fxstat case is harder. The original declaration of
__fxstat and the extern inline (that is, 'extern __inline
__attribute__ ((__gnu_inline__))') definition of fstat (which calls
__fxstat) is in the installed header, while the hidden_proto (i.e.
redeclaration with asm label) is in the wrapper header (and
necessarily must come after the #include of the installed header).
A GNU extern inline case is one where the rationale I mentioned in
https://llvm.org/bugs/show_bug.cgi?id=22830#c1 for Clang not being
able to match GCC's semantics might not really apply: you never need
to emit the code for fstat before the redeclaration, because you only
ever inline it and never emit an actual function.
Perhaps there is a defensible reason that Clang really cannot match
the GNU semantics even for this case. Regardless, Clang really needs
to thoroughly document its semantics for every language extension when
its semantics are not completely identical to the GNU language
extension's semantics.
If Clang's asm labels extension persists in having semantics
incompatible with the original semantics of the asm labels extension
invented by GNU, we might be able to work around it adequately in the
glibc build just by making sure __USE_EXTERN_INLINES is not defined
during the build.
On Mon, Jan 4, 2016 at 3:39 PM, Kostya Serebryany <kcc at google.com> wrote:
> Thanks for checking, Nick!
> +Roland, FYI (recent changes in clang break compilation of all of the
> glibc),
> similar to https://llvm.org/bugs/show_bug.cgi?id=22830#c1
>
> On Mon, Jan 4, 2016 at 3:21 PM, Nick Lewycky <nicholas at mxc.ca> wrote:
>>
>> On 01/04/2016 01:40 PM, Kostya Serebryany wrote:
>>>
>>>
>>>
>>> On Thu, Dec 17, 2015 at 5:03 PM, Richard Smith <richard at metafoo.co.uk
>>> <mailto:richard at metafoo.co.uk>> wrote:
>>>
>>> On Thu, Dec 17, 2015 at 3:59 PM, Nick Lewycky via cfe-commits
>>> <cfe-commits at lists.llvm.org <mailto:cfe-commits at lists.llvm.org>>
>>> wrote:
>>>
>>> On 12/17/2015 10:47 AM, Kostya Serebryany wrote:
>>>
>>> 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?
>>>
>>>
>>> Could you email me a .i copy of a failing build? That will help
>>> me decide whether it's a bug in the error or in glibc.
>>>
>>>
>>> [sorry for delay,]
>>> here is the preprocessed source file from glibc:
>>> % clang ~/tmp/a.i 2>&1 | grep error:
>>> ../include/sys/stat.h:16:28: error: cannot apply asm label to function
>>> after its first use
>>> ../include/sys/stat.h:17:30: error: cannot apply asm label to function
>>> after its first use
>>> ../include/sys/stat.h:18:28: error: cannot apply asm label to function
>>> after its first use
>>> ../include/sys/stat.h:19:30: error: cannot apply asm label to function
>>> after its first use
>>> ...
>>>
>>>
>>> Also PR22830 comment 1 seems relevant here.
>>>
>>>
>>> Probably, but since this is a very recent regression in clang I thought
>>> I should report it.
>>
>>
>> This looks like it's WAI:
>>
>> 3783 extern int __fxstat (int __ver, int __fildes, struct stat
>> *__stat_buf)
>> 3784 __attribute__ ((__nothrow__ )) ;
>> ...
>> 3827 extern __inline int
>> 3828 __attribute__ ((__nothrow__ )) fstat (int __fd, struct stat
>> *__statbuf)
>> 3829 {
>> 3830 return __fxstat (1, __fd, __statbuf);
>> 3831 }
>> ...
>> 3910 extern __typeof (__fxstat) __fxstat __asm__ ("" "__GI___fxstat")
>> __attribute__ ((visibility ("hidden")));
>>
>> This is exactly the situation where GCC and Clang will emit a different .o
>> file.
>>
>> Nick
>>
>>> On Fri, Dec 11, 2015 at 1:28 PM, Nick Lewycky via cfe-commits
>>> <cfe-commits at lists.llvm.org
>>> <mailto:cfe-commits at lists.llvm.org>
>>> <mailto:cfe-commits at lists.llvm.org
>>>
>>> <mailto: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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>>
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