On Mon, Jan 4, 2016 at 4:04 PM, Roland McGrath <mcgra...@google.com> wrote:
> Kostya, do you remember the exact original case in glibc for 22830 and > what glibc change fixed it? > Sadly, no. I only know that the code was reduced from the code that was setting these attributes for strtol. 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 <k...@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 <nicho...@mxc.ca> wrote: > >> > >> On 01/04/2016 01:40 PM, Kostya Serebryany wrote: > >>> > >>> > >>> > >>> On Thu, Dec 17, 2015 at 5:03 PM, Richard Smith <rich...@metafoo.co.uk > >>> <mailto:rich...@metafoo.co.uk>> wrote: > >>> > >>> On Thu, Dec 17, 2015 at 3:59 PM, Nick Lewycky via cfe-commits > >>> <cfe-commits@lists.llvm.org <mailto:cfe-commits@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@lists.llvm.org > >>> <mailto:cfe-commits@lists.llvm.org> > >>> <mailto:cfe-commits@lists.llvm.org > >>> > >>> <mailto:cfe-commits@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(); } > >>> > >>> > >>> _______________________________________________ > >>> cfe-commits mailing list > >>> cfe-commits@lists.llvm.org > >>> <mailto:cfe-commits@lists.llvm.org> > >>> <mailto:cfe-commits@lists.llvm.org > >>> <mailto:cfe-commits@lists.llvm.org>> > >>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits > >>> > >>> > >>> > >>> _______________________________________________ > >>> cfe-commits mailing list > >>> cfe-commits@lists.llvm.org <mailto:cfe-commits@lists.llvm.org> > >>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits > >>> > >>> > >>> > >> > > >
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