[Bug target/40411] -std=c99 does not enable c99 mode in Solaris C library

[heydowns at borg dot com]

------- Comment #12 from heydowns at borg dot com  2009-07-10 14:41 -------
Trying to give some answers to Joseph's questions in comment 9.

The best documentation I found on what, exactly, the various object files do is
actually the man pages for the Sun Studio compilers and the OpenSolaris source
code for values-*.c

Choice of values-xpg*.o and values-X*.o are someone independent, so I'm
splitting up the explanation.


First, values-xpg*.o:

Link Tool & Flags          Link Result            Comment
c89                        values-xpg4.o
c99                        values-xpg6.o
cc -xc99=all,no_lib        Neither                Default -xc99 option
                                                  c99 language features, 
                                                  no c99 library support
cc -xc99=all               values-xpg6.o          c99 lang feat. & lib support
cc -xc99=none              Neither                No c99 at all

So, values-xpg6.o clearly enables c99 behavior of system libraries where there
is a runtime difference.  It also enables the preference of XPG4 behavior over
XPG3 behavior (as below).

>From looking at the OpenSolaris source code for values-xpg4.o, it is stated
that linking in that object file enables "xpg4 mode for APIs which have
differing runtime behavior from xpg3 to xpg4".

Lastly, from man page 'standards', the only time "cc" is recommended as a
compiler (instead of c89 or c99, and thus not linking any of values-xpg*.o) is
when you want to conform to SVID3 or CAE XPG3. 

What is the runtime difference of xpg3 versus xpg4?  I really don't know -
maybe someone can help here.

But, back to Joseph's question, the inclusion values-xpg*.o does not seem to
deal with extensions to standard behavior; rather it does sound like it
controls the standard to which functions should conform. Based on this I am
leaning towards saying values-xpg4.o should be enabled for -std=gnu89.  I'd
appreciate comments in light of the above.  (please note that this would make
it non-trivial to link for xpg3 behavior).


values-X{c,a,t,s}.o are what seem to control how strict the implementation
follows the standard.  Currently gcc only ever uses values-X{a,c}.o which is
probably sufficient, and I don't think that this needs to change at all:

-std=gnu*   -> values-Xa.o
otherwise   -> values-Xc.o

values-Xa is described as "ANSI conforming mode" whereas -Xc is "Strict ANSI
mode" in the Open Solaris sources. 

The 'cc' man page documents -Xa as ISO C plus K&R C compatibility extensions,
plus semantic changes required by ISO C, preferring ISO C semantics where there
is conflict.
-Xc is documented as "Strictly conforming" ISO C, no K&R extensions.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40411