Re: [patch] Remove NO_IMPLICIT_EXTERN_C target macro

[Steven Bosscher <stevenb dot gcc at gmail dot com>]

On Mon, Jun 18, 2012 at 1:12 PM, Joseph S. Myers
<joseph@codesourcery.com> wrote:
> On Mon, 18 Jun 2012, Steven Bosscher wrote:
>
>> For targets that do not define NO_IMPLICIT_EXTERN_C, GCC assumes that
>> included system headers are implicitly wrapped in 'extern "C" {...}'.
>> I could not find where this target macro was introduced, but it is
>> very old (it is already mentioned in FSFChangeLog.10 for a change in
>> 1995). AFAICT, today all supported targets have C++-compatible headers
>
> May have been introduced by:
>
> Fri Nov ?5 05:48:04 1993 ?Richard Stallman ?(rms@mole.gnu.ai.mit.edu)
>
> ? ? ? ?* cccp.c (main): Handle NO_IMPLICIT_EXTERN_C.
>
>> (according to one comment, even hpux8 had C++-compatible system
>> headers :-), so NO_IMPLICIT_EXTERN_C shouldn't be necessary anymore.
>
> It was previously said that AIX headers needed it
> <http://gcc.gnu.org/ml/gcc/2005-05/msg00381.html>. ?That of course was AIX
> headers as of 2005; I don't know whether seven years later any version of
> AIX supported by GCC trunk still needs this.

AFAICT,  the oldest supported version is AIX 4.3, from 1997. Given
that HP-UX 8 already had C++ compatible headers in 1991, one would
hope that AIX 4.3 had its headers fixed also, several years after
HP-UX 8.


>> The only target that explicitly undefines NO_IMPLICIT_EXTERN_C is
>> sparc64-openbsd, and I find it hard to believe that the system headers
>> on openbsd are not also already C++-compatible. Marc, could you have a
>> look at this, please?
>
> What targets (such as AIX?) did not explicitly undefine it, but did not
> get a definition from any header they used either? ?It's quite likely some
> such targets *should* have had NO_IMPLICIT_EXTERN_C defined, but not
> necessarily all of them.

The following OSs all have NO_IMPLICIT_EXTERN_C defined:

darwin.h:#define NO_IMPLICIT_EXTERN_C
freebsd.h:#define NO_IMPLICIT_EXTERN_C  1
gnu-user.h:#define NO_IMPLICIT_EXTERN_C (covers all glibc and
glibc-derived targets).
lynx.h:# define NO_IMPLICIT_EXTERN_C
netbsd.h:#define NO_IMPLICIT_EXTERN_C    1
rtems.h:#define NO_IMPLICIT_EXTERN_C
sol2.h:#define NO_IMPLICIT_EXTERN_C
vx-common.h:#define NO_IMPLICIT_EXTERN_C

So all the major OSs are covered. I'm not sure how Bionic is covered, though.

Since your list (http://gcc.gnu.org/ml/gcc/2005-05/msg00377.html) the
following things have changed:

The following targets have been fixed (i.e. now do define NO_IMPLICIT_EXTERN_C):
arm-wrs-vxworks
i[34567]86-*-darwin*
i[4567]86-wrs-vxworks
m68k-*-uclinux*
mipsisa32-*-elf* (via config/mips/elf.h)
mipsisa32el-*-elf*
mipsisa32r2-*-elf*
mipsisa32r2el-*-elf*
mipsisa64-*-elf*
mipsisa64el-*-elf*
mipsisa64sr71k-*-elf*
mipsisa64sb1-*-elf*
mipsisa64sb1el-*-elf*
mips-*-elf*
mipsel-*-elf*
mips64-*-elf*
mips64el-*-elf*
mips64vr-*-elf*
mips64vrel-*-elf*
mips64orion-*-elf*
mips64orionel-*-elf*
mips-wrs-vxworks
mips-wrs-windiss
mipstx39-*-elf*
mipstx39el-*-elf*
powerpc-*-darwin*
v850e1-*-* (via config/v850/v850.h)
v850e-*-*
v850-*-*


The following have been removed:
arc-*-elf*
arm-*-coff*
armel-*-coff*
arm-semi-aof
armel-semi-aof
arm*-*-ecos-elf
arm*-*-elf
ep9312-*-elf (this is a --with-arch for arm*-*-*)
arm*-wince-pe*
arm-*-pe*
arm*-*-kaos*
c4x-* (other than c4x-*-rtems*)
tic4x-* (other than tic4x-*-rtems*)
hppa1.1-*-osf*
hppa1.1-*-bsd*
i[34567]86-sequent-ptx4*
i[34567]86-sequent-sysv4*
i[34567]86-*-aout*
i[34567]86-*-coff*
i[3456x]86-*-netware*
i[34567]86-*-sysv5*
i[34567]86-*-sysv4*
i[34567]86-*-uwin*
i[34567]86-*-kaos*
i860-*-sysv4*
ip2k-*-elf
m68hc11-*-*
m6811-*-*
m68hc12-*-*
m6812-*-*
m68k-*-aout*
m68k-*-coff*
m68020-*-elf*
mcore-*-pe*
mn10300-*-*
pdp11-*-bsd
powerpc-*-beos*
sparc-*-openbsd* (apparently only sparc64-openbsd is still supported)
sparc-*-sysv4*
strongarm-*-elf*
strongarm-*-pe
strongarm-*-kaos*
vax-*-bsd*
vax-*-sysv*
vax-*-ultrix*
xscale-*-elf
xscale-*-coff


The following targets do not define NO_IMPLICIT_EXTERN_C (mostly
openbsd, aix, and generic ELF targets):
arm*-*-eabi*
arm*-*-symbianelf*
avr-*-* (other than avr-*-rtems*)
bfin*-elf*
bfin*-*
fr30-*-elf
frv-*-elf
h8300-*-* (other than h8300-*-rtems*)
i[34567]86-*-elf*
ia64*-*-elf*
iq2000*-*-elf*
m32r-*-elf*
m32rle-*-elf*
m68k-*-elf*
mcore-*-elf
pdp11-*-*
sh*-*-* (other than sh*-*-linux*, sh*-*-netbsd*, sh-wrs-vxworks, and
sh*-*-rtems*)
rs6000-ibm-aix4.[12]*
powerpc-ibm-aix4.[12]*
rs6000-ibm-aix4.[3456789]*
powerpc-ibm-aix4.[3456789]*
rs6000-ibm-aix5.1.*
powerpc-ibm-aix5.1.*
rs6000-ibm-aix[56789].*
powerpc-ibm-aix[56789].*
i[34567]86-*-openbsd2.*
i[34567]86-*openbsd3.[0123]
i[34567]86-*-openbsd*
m68k*-*-openbsd*
mips*-*-openbsd*
sparc64-*-openbsd* (deliberate #undef)
vax-*-openbsd*

Ciao!
Steven