On Sun, 2016-01-17 at 18:30 -0500, David Edelsohn wrote:
> On Sun, Jan 17, 2016 at 3:21 PM, Torvald Riegel <[email protected]> wrote:
> > On Sat, 2016-01-16 at 15:38 -0500, David Edelsohn wrote:
> >> On Sat, Jan 16, 2016 at 8:35 AM, Jakub Jelinek <[email protected]> wrote:
> >> > On Sat, Jan 16, 2016 at 07:47:33AM -0500, David Edelsohn wrote:
> >> >> stage1 libstdc++ builds just fine. the problem is stage2 configure
> >> >> fails due to missing ITM_xxx symbols when configure tries to compile
> >> >> and run conftest programs.
> >> >
> >> > On x86_64-linux, the _ITM_xxx symbols are undef weak ones and thus it is
> >> > fine to load libstdc++ without libitm and libstdc++ doesn't depend on
> >> > libitm.
> >> >
> >> > So, is AIX defining __GXX_WEAK__ or not? Perhaps some other macro or
> >> > configure check needs to be used to determine if undefined weak symbols
> >> > work the way libstdc++ needs them to.
> >>
> >> __GXX_WEAK__ appears to be defined by gcc/c-family/c-cppbuiltin.c
> >> based on SUPPORTS_ONE_ONLY. gcc/defaults.h defines SUPPORTS_ONE_ONLY
> >> if the target supports MAKE_DECL_ONE_ONLY and link-once semantics.
> >> AIX weak correctly supports link-once semantics. AIX also supports
> >> the definition of __GXX_WEAK__ in gcc/doc/cpp.texi, namely collapsing
> >> symbols with vague linkage in multiple translation units.
> >>
> >> libstdc++/src/c++11/cow-stdexcept.cc appears to be using __GXX_WEAK__
> >> and __attribute__ ((weak)) for references to symbols that may not be
> >> defined at link time or run time. AIX does not allow undefined symbol
> >> errors by default. And the libstdc++ inference about the semantics of
> >> __GXX_WEAK__ are different than the documentation.
> >>
> >> AIX supports MAKE_DECL_ONE_ONLY and the documented meaning of
> >> __GXX_WEAK__. AIX does not support extension of the meaning to
> >> additional SVR4 semantics not specified in the documentation.
> >
> > I see, so we might be assuming that __GXX_WEAK__ means more than it
> > actually does (I'm saying "might" because personally, I don't know; your
> > information supports this is the case, but the initial info I got was
> > that __GXX_WEAK__ would mean we could have weak decls without
> > definitions).
>
> I believe that libstdc++ must continue with the weak undefined
> references to the symbols as designed, but protect them with a
> different macro. For example, __GXX_WEAK_REF__ or __GXX_WEAK_UNDEF__
> defined in defaults.h based on configure test or simply overridden in
> config/rs6000/aix.h. Or the macro could be local to libstdc++ and
> overridden in config/os/aix/os_defines.h.
OK. I'm currently testing the attached patch on x86_64-linux. David,
if there are no objections from you and those CC'ed, could you give this
one a try on AIX, please?
* include/bits/c++config (_GLIBCXX_USE_WEAK_REF): New.
(_GLIBCXX_TXN_SAFE, _GLIBCXX_TXN_SAFE_DYN): Use _GLIBCXX_USE_WEAK_REF
and move after its definition.
* config/os/aix/os_defines.h (_GLIBCXX_USE_WEAK_REF): Override.
* src/c++11/cow-stdexcept.cc: Use _GLIBCXX_USE_WEAK_REF instead of
__GXX_WEAK__, and only provide transactional clones if
_GLIBCXX_USE_WEAK_REF is true. Don't provide stubs of libitm
functions.
commit a5a8819bce824815a94ef8d58f6d4123db92f1d4
Author: Torvald Riegel <[email protected]>
Date: Mon Jan 18 14:42:21 2016 +0100
libstdc++: Fix usage of __GXX_WEAK__ in TM TS support.
* include/bits/c++config (_GLIBCXX_USE_WEAK_REF): New.
(_GLIBCXX_TXN_SAFE, _GLIBCXX_TXN_SAFE_DYN): Use _GLIBCXX_USE_WEAK_REF
and move after its definition.
* config/os/aix/os_defines.h (_GLIBCXX_USE_WEAK_REF): Override.
* src/c++11/cow-stdexcept.cc: Use _GLIBCXX_USE_WEAK_REF instead of
__GXX_WEAK__, and only provide transactional clones if
_GLIBCXX_USE_WEAK_REF is true. Don't provide stubs of libitm
functions.
diff --git a/libstdc++-v3/config/os/aix/os_defines.h b/libstdc++-v3/config/os/aix/os_defines.h
index d895471..0949446 100644
--- a/libstdc++-v3/config/os/aix/os_defines.h
+++ b/libstdc++-v3/config/os/aix/os_defines.h
@@ -48,4 +48,7 @@
#define __COMPATMATH__
#endif
+// No support for referencing weak symbols without a definition.
+#define _GLIBCXX_USE_WEAK_REF 0
+
#endif
diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
index 387a7bb..57024e4 100644
--- a/libstdc++-v3/include/bits/c++config
+++ b/libstdc++-v3/include/bits/c++config
@@ -483,20 +483,6 @@ namespace std
#define _GLIBCXX_USE_ALLOCATOR_NEW
-// Conditionally enable annotations for the Transactional Memory TS on C++11.
-// Most of the following conditions are due to limitations in the current
-// implementation.
-#if __cplusplus >= 201103L && _GLIBCXX_USE_CXX11_ABI \
- && _GLIBCXX_USE_DUAL_ABI && __cpp_transactional_memory >= 201505L \
- && !_GLIBCXX_FULLY_DYNAMIC_STRING && __GXX_WEAK__ \
- && _GLIBCXX_USE_ALLOCATOR_NEW
-#define _GLIBCXX_TXN_SAFE transaction_safe
-#define _GLIBCXX_TXN_SAFE_DYN transaction_safe_dynamic
-#else
-#define _GLIBCXX_TXN_SAFE
-#define _GLIBCXX_TXN_SAFE_DYN
-#endif
-
#else // !__cplusplus
# define _GLIBCXX_BEGIN_EXTERN_C
# define _GLIBCXX_END_EXTERN_C
@@ -524,6 +510,28 @@ namespace std
# define _GLIBCXX_WEAK_DEFINITION
#endif
+// By default, we assume that __GXX_WEAK__ also means that there is support
+// for declaring functions as weak while not defining such functions. This
+// allows for referring to functions provided by other libraries (e.g.,
+// libitm) without depending on them if the respective features are not used.
+#ifndef _GLIBCXX_USE_WEAK_REF
+# define _GLIBCXX_USE_WEAK_REF __GXX_WEAK__
+#endif
+
+// Conditionally enable annotations for the Transactional Memory TS on C++11.
+// Most of the following conditions are due to limitations in the current
+// implementation.
+#if __cplusplus >= 201103L && _GLIBCXX_USE_CXX11_ABI \
+ && _GLIBCXX_USE_DUAL_ABI && __cpp_transactional_memory >= 201505L \
+ && !_GLIBCXX_FULLY_DYNAMIC_STRING && _GLIBCXX_USE_WEAK_REF \
+ && _GLIBCXX_USE_ALLOCATOR_NEW
+#define _GLIBCXX_TXN_SAFE transaction_safe
+#define _GLIBCXX_TXN_SAFE_DYN transaction_safe_dynamic
+#else
+#define _GLIBCXX_TXN_SAFE
+#define _GLIBCXX_TXN_SAFE_DYN
+#endif
+
// The remainder of the prewritten config is automatic; all the
// user hooks are listed above.
diff --git a/libstdc++-v3/src/c++11/cow-stdexcept.cc b/libstdc++-v3/src/c++11/cow-stdexcept.cc
index eddb36b..a0f505c 100644
--- a/libstdc++-v3/src/c++11/cow-stdexcept.cc
+++ b/libstdc++-v3/src/c++11/cow-stdexcept.cc
@@ -179,6 +179,13 @@ _GLIBCXX_END_NAMESPACE_VERSION
// Furthermore, _Rep will always have been allocated or deallocated via
// global new or delete, so nontransactional writes we do to _Rep cannot
// interfere with transactional accesses.
+
+// We depend on having support for referencing functions declared weak that
+// are not defined by us. Without such support, the exceptions will not be
+// declared transaction-safe, so we just don't provide transactional clones
+// in this case.
+#if _GLIBCXX_USE_WEAK_REF
+
extern "C" {
#ifndef _GLIBCXX_MANGLE_SIZE_T
@@ -195,7 +202,6 @@ extern "C" {
# define ITM_REGPARM
#endif
-#if __GXX_WEAK__
// Declare all libitm symbols we rely on, but make them weak so that we do
// not depend on libitm.
extern void* _ZGTtnaX (size_t sz) __attribute__((weak));
@@ -213,19 +219,6 @@ extern void _ITM_memcpyRnWt(void *, const void *, size_t)
extern void _ITM_addUserCommitAction(void (*)(void *), uint64_t, void *)
ITM_REGPARM __attribute__((weak));
-#else
-// If there is no support for weak symbols, create dummies. The exceptions
-// will not be declared transaction_safe in this case.
-void* _ZGTtnaX (size_t) { return NULL; }
-void _ZGTtdlPv (void*) { }
-uint8_t _ITM_RU1(const uint8_t *) { return 0; }
-uint32_t _ITM_RU4(const uint32_t *) { return 0; }
-uint64_t _ITM_RU8(const uint64_t *) { return 0; }
-void _ITM_memcpyRtWn(void *, const void *, size_t) { }
-void _ITM_memcpyRnWt(void *, const void *, size_t) { }
-void _ITM_addUserCommitAction(void (*)(void *), uint64_t, void *) { };
-#endif
-
}
// A transactional version of basic_string::basic_string(const char *s)
@@ -441,3 +434,5 @@ CTORDTOR(14overflow_error, std::overflow_error, runtime_error)
CTORDTOR(15underflow_error, std::underflow_error, runtime_error)
}
+
+#endif // _GLIBCXX_USE_WEAK_REF
