Hi!
GCC used to emit an instance of an empty ios_base::Init class in
every TU which included <iostream> to ensure it is std::cout etc.
is initialized, but thanks to Patrick work on some targets (which have
init_priority attribute support) it is now initialized only inside of
libstdc++.so.6/libstdc++.a.
This causes a problem if people do something that has never been supported,
try to run GCC 13 compiled C++ code against GCC 12 or earlier
libstdc++.so.6 - std::cout etc. are then never initialized because code
including <iostream> expects the library to initialize it and the library
expects code including <iostream> to do that.
The following patch is second attempt to make this work cheaply as the
earlier attempt of aliasing the std::cout etc. symbols with another symbol
version didn't work out due to copy relocation breaking the aliases appart.
The patch forces just a _ZSt21ios_base_library_initv undefined symbol
into all *.o files which include <iostream> and while there is no runtime
relocation against that, it seems to enforce the right version of
libstdc++.so.6. /home/jakub/src/gcc/obj08i/usr/local/ is the install
directory of trunk patched with this patch, /home/jakub/src/gcc/obj06/
is builddir of trunk without this patch, system g++ is GCC 12.1.1.
$ cat /tmp/hw.C
#include <iostream>
int
main ()
{
std::cout << "Hello, world!" << std::endl;
}
$ cd /home/jakub/src/gcc/obj08i/usr/local/bin
$ ./g++ -o /tmp/hw /tmp/hw.C
$ readelf -Wa /tmp/hw 2>/dev/null | grep initv
4: 0000000000000000 0 FUNC GLOBAL DEFAULT UND
_ZSt21ios_base_library_initv@GLIBCXX_3.4.32 (4)
71: 0000000000000000 0 FUNC GLOBAL DEFAULT UND
_ZSt21ios_base_library_initv@GLIBCXX_3.4.32
$ /tmp/hw
/tmp/hw: /lib64/libstdc++.so.6: version `GLIBCXX_3.4.32' not found (required by
/tmp/hw)
$ LD_LIBRARY_PATH=/home/jakub/src/gcc/obj08i/usr/local/lib64/ /tmp/hw
Hello, world!
$
LD_LIBRARY_PATH=/home/jakub/src/gcc/obj06/x86_64-pc-linux-gnu/libstdc++-v3/src/.libs/
/tmp/hw
/tmp/hw:
/home/jakub/src/gcc/obj06/x86_64-pc-linux-gnu/libstdc++-v3/src/.libs/libstdc++.so.6:
version `GLIBCXX_3.4.32' not found (required by /tmp/hw)
$ g++ -o /tmp/hw /tmp/hw.C
$ /tmp/hw
Hello, world!
$
LD_LIBRARY_PATH=/home/jakub/src/gcc/obj06/x86_64-pc-linux-gnu/libstdc++-v3/src/.libs/
/tmp/hw
Hello, world!
$ LD_LIBRARY_PATH=/home/jakub/src/gcc/obj08i/usr/local/lib64/ /tmp/hw
Hello, world!
Bootstrapped/regtested on x86_64-linux, i686-linux and sparc-sun-solaris2.11
On the last one I've actually checked a version which had
defined(_GLIBCXX_SYMVER_SUN) next to defined(_GLIBCXX_SYMVER_GNU), but
init_priority attribute doesn't seem to be supported there and so I couldn't
actually test how this works there. Using gas and Sun ld, Rainer, does one
need to use gas + gld for init_priority or something else?
Ok for trunk and after a while for GCC 13.2?
2023-04-28 Jakub Jelinek <ja...@redhat.com>
PR libstdc++/108969
* config/abi/pre/gnu.ver (GLIBCXX_3.4.32): Export
_ZSt21ios_base_library_initv.
* testsuite/util/testsuite_abi.cc (check_version): Add GLIBCXX_3.4.32
symver and make it the latestp.
* src/c++98/ios_init.cc (ios_base_library_init): New alias.
* acinclude.m4 (libtool_VERSION): Change to 6:32:0.
* include/std/iostream: If init_priority attribute is supported
and _GLIBCXX_SYMVER_GNU, force undefined _ZSt21ios_base_library_initv
symbol into the object.
* configure: Regenerated.
--- libstdc++-v3/config/abi/pre/gnu.ver.jj 2023-04-20 09:36:09.415371050
+0200
+++ libstdc++-v3/config/abi/pre/gnu.ver 2023-04-27 17:58:44.599675359 +0200
@@ -2514,6 +2514,10 @@ GLIBCXX_3.4.31 {
} GLIBCXX_3.4.30;
+GLIBCXX_3.4.32 {
+ _ZSt21ios_base_library_initv;
+} GLIBCXX_3.4.31;
+
# Symbols in the support library (libsupc++) have their own tag.
CXXABI_1.3 {
--- libstdc++-v3/testsuite/util/testsuite_abi.cc.jj 2023-01-16
11:52:17.495713257 +0100
+++ libstdc++-v3/testsuite/util/testsuite_abi.cc 2023-04-27
17:30:39.651173917 +0200
@@ -213,6 +213,7 @@ check_version(symbol& test, bool added)
known_versions.push_back("GLIBCXX_LDBL_3.4.29");
known_versions.push_back("GLIBCXX_3.4.30");
known_versions.push_back("GLIBCXX_3.4.31");
+ known_versions.push_back("GLIBCXX_3.4.32");
known_versions.push_back("GLIBCXX_LDBL_3.4.31");
known_versions.push_back("GLIBCXX_IEEE128_3.4.29");
known_versions.push_back("GLIBCXX_IEEE128_3.4.30");
@@ -251,7 +252,7 @@ check_version(symbol& test, bool added)
test.version_status = symbol::incompatible;
// Check that added symbols are added in the latest pre-release version.
- bool latestp = (test.version_name == "GLIBCXX_3.4.31"
+ bool latestp = (test.version_name == "GLIBCXX_3.4.32"
// XXX remove next 2 lines when baselines have been regenerated.
|| test.version_name == "GLIBCXX_IEEE128_3.4.31"
|| test.version_name == "GLIBCXX_LDBL_3.4.31"
--- libstdc++-v3/src/c++98/ios_init.cc.jj 2023-01-16 11:52:16.995720625
+0100
+++ libstdc++-v3/src/c++98/ios_init.cc 2023-04-27 18:34:46.121276617 +0200
@@ -199,5 +199,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
return __ret;
}
+#ifdef _GLIBCXX_SYMVER_GNU
+ void ios_base_library_init (void)
+ __attribute__((alias ("_ZNSt8ios_base4InitC1Ev")));
+#endif
+
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
--- libstdc++-v3/acinclude.m4.jj 2023-02-02 09:53:31.745525704 +0100
+++ libstdc++-v3/acinclude.m4 2023-04-27 17:27:51.071626279 +0200
@@ -3841,7 +3841,7 @@ changequote([,])dnl
fi
# For libtool versioning info, format is CURRENT:REVISION:AGE
-libtool_VERSION=6:31:0
+libtool_VERSION=6:32:0
# Everything parsed; figure out what files and settings to use.
case $enable_symvers in
--- libstdc++-v3/include/std/iostream.jj 2023-01-16 11:52:16.968721023
+0100
+++ libstdc++-v3/include/std/iostream 2023-04-27 18:34:07.479837226 +0200
@@ -77,6 +77,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// in the compiled library instead (src/c++98/globals_io.cc).
#if !__has_attribute(__init_priority__)
static ios_base::Init __ioinit;
+#elif defined(_GLIBCXX_SYMVER_GNU)
+ __extension__ __asm (".globl _ZSt21ios_base_library_initv");
#endif
_GLIBCXX_END_NAMESPACE_VERSION
--- libstdc++-v3/configure.jj 2023-02-02 09:53:31.795524981 +0100
+++ libstdc++-v3/configure 2023-04-27 17:29:13.263429963 +0200
@@ -68652,7 +68652,7 @@ $as_echo "$as_me: WARNING: === Symbol ve
fi
# For libtool versioning info, format is CURRENT:REVISION:AGE
-libtool_VERSION=6:31:0
+libtool_VERSION=6:32:0
# Everything parsed; figure out what files and settings to use.
case $enable_symvers in
Jakub
