Hi, Reviving an old thread from February 2010. In <http://lists.gnu.org/archive/html/autoconf/2010-02/msg00013.html> Peter O'Gorman wrote: > When creating a library or application with c99 or cc -xc99=all > /usr/lib/values-xpg6.o is included in the output, this object file > contains the c99 definitions for __xpg4 and __xpg6. When creating output > without c99/-xc99=all this extra object is not put into the output and > the values of __xpg4 and __xpg6 in libc (c89 behavior) are used (because > they are the only definitions available). I confirm with a test program. ========================== foo.c ======================= #include <stdio.h> int main () { printf ("%f\n", 1.0 / 0.0); return 0; } ======================================================== POSIX:2008 says that the output should be "inf". $ /opt/solstudio12.2/bin/cc foo.c && ./a.out Inf $ nm a.out | grep values [34] | 0| 0|FILE |LOCL |0 |ABS |values-Xa.c $ /opt/solstudio12.2/bin/cc -xc99=all foo.c && ./a.out inf $ nm a.out | grep values [34] | 0| 0|FILE |LOCL |0 |ABS |values-Xa.c [36] | 0| 0|FILE |LOCL |0 |ABS |values-xpg6.c $ gcc foo.c && ./a.out Inf $ gcc foo.c /usr/lib/values-xpg4.o && ./a.out Inf $ gcc foo.c /usr/lib/values-xpg6.o && ./a.out inf $ gcc -std=gnu99 foo.c && ./a.out Inf $ gcc -std=gnu99 foo.c /usr/lib/values-xpg6.o && ./a.out inf So, it's clear that - the presence of values-xpg6.c in the executable causes printf() to behave differently, - values-xpg6.c is implicit in the link command line of "cc -xc99=all", but not of "cc", "gcc", "gcc -std=gnu99". > Also, does anyone happen to know what exactly libc does differently > with __xpg4=1 (the __xpg6 settings are documented in > http://src.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/lib/libc/inc/xpg6.h Grepping through the OpenSolaris source code, I find references to __xpg4 in libc/port/sys/libc_open.c libc/port/sys/libc_link.c libc/port/gen/execvp.c libc/port/gen/sysconf.c libc/port/stdio/system.c libc/port/stdio/_filbuf.c libc/port/stdio/popen.c libc/port/print/doprnt.c libc/port/threads/spawn.c libc/port/threads/thr.c libc/port/regex/wordexp.c libc/inc/libc.h and to __xpg6 in libc/port/gen/strtod.c libc/port/gen/sysconf.c libc/port/gen/confstr.c libc/port/stdio/fopen.c libc/port/stdio/doscan.c libc/port/print/doprnt.c libc/port/threads/thr.c libc/port/i18n/wstod.c libc/inc/xpg6.h Ralf Wildenhues asked in <http://lists.gnu.org/archive/html/autoconf/2010-02/msg00014.html> > Do I understand correctly that effectively, that makes all code relying > on one behavior silently link-incompatible with all code relying on the > other behavior, but either of them still compatible with code that > doesn't care? Yes. And the "xpg6" flag can sit in the program and have an effect on the libraries, just as it can sit in a library and have an effect on the rest of the code in the program. Test case: $ cat libinf.c #include <stdio.h> void libinf (void) { printf ("%f\n", 1.0 / 0.0); } $ cat foo.c #include <stdio.h> extern void libinf (void); int main () { printf ("In lib: "); libinf (); printf ("In main: %f\n", 1.0 / 0.0); return 0; } $ gcc -shared -fPIC libinf.c -o libinf.so $ gcc foo.c libinf.so -R `pwd` $ ./a.out In lib: Inf In main: Inf $ gcc -shared -fPIC libinf.c -o libinf.so $ gcc foo.c /usr/lib/values-xpg6.o libinf.so -R `pwd` $ ./a.out In lib: inf In main: inf $ gcc -shared -fPIC libinf.c /usr/lib/values-xpg6.o -o libinf.so $ gcc foo.c libinf.so -R `pwd` $ ./a.out In lib: inf In main: inf $ gcc -shared -fPIC libinf.c /usr/lib/values-xpg6.o -o libinf.so $ gcc foo.c /usr/lib/values-xpg6.o libinf.so -R `pwd` $ ./a.out In lib: inf In main: inf Bob Friesenhahn asked in <http://lists.gnu.org/archive/html/autoconf/2010-02/msg00015.html>: > if GCC and GNU ld participate in this scheme under Solaris. As far as GCC 4.5.2, the answer from grepping the source code is no. There is a bug open about this, though: <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40411> I hope this flag won't be used by GCC, because it's a bad idea, just like the _fmode variable on Windows. The right way to distinguish desired standards conformance, in a way that works fine with libraries, is through preprocessor defines (such as __EXTENSIONS__, _FILE_OFFSET_BITS, etc.). This technique is used in Solaris in some places (ttyname_r, getlogin_r, sysconf, putmsg etc.); no idea why the implementors went the wrong way for printf and other functions. Bruno _______________________________________________ Autoconf mailing list Autoconf@xxxxxxx http://lists.gnu.org/mailman/listinfo/autoconf
