Re: [PATCH 1/2] Enable C++

Re: [PATCH 1/2] Enable C++

[Petr Machata]

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Mark Wielaard <mjw@redhat.com> writes:

> I was mostly wondering whether we needed to add an command line argument
> like -std=gnu++98 to be sure. But maybe that is all implicit and
> standard for all gcc versions anyway.

Actually I can't find code that c++98 mode would reject and gnu++98
would allow.  -pedantic makes all the difference, and it makes it
regardless of the dialect chosen.

Which makes it kinda hard to actually test for gnu++98 support.  Which I
think we formally need, for all the GNU C stuff that we get in C headers
((struct X) {blah, blah}, long long literals, __VA_ARGS__).  But GCC
happily compiles that in c++98 mode anyway.

So, I don't know.  Maybe I just compile the test case with -std=gnu++98
and make it "Checking for working C++ compiler that accepts -std=gnu++98"?

Clang knows about the option as well, FWIW.

Thanks,
Petr

Re: [PATCH 1/2] Enable C++

[Mark Wielaard]

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On Tue, 2015-04-14 at 16:37 +0200, Petr Machata wrote:
> I think this was mostly agreed on.  The change since last time is that
> we pass -std=gnu++98 when testing C++ compiler existence, for
> correctness' sake.

Yes, looks fine.

Thanks,

Mark

[PATCH 1/2] Enable C++

[Petr Machata]

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Hi there,

I think this was mostly agreed on.  The change since last time is that
we pass -std=gnu++98 when testing C++ compiler existence, for
correctness' sake.

Thanks,
Petr

--- 8< -----------------------------------------------------------
- Detect C++ compiler in configure, add supporting infrastructure to
  eu.am.

Signed-off-by: Petr Machata <pmachata@redhat.com>
---
 ChangeLog        |  4 ++++
 config/ChangeLog |  6 ++++++
 config/eu.am     | 21 ++++++++++++++++++++-
 configure.ac     | 28 ++++++++++++++++++++++++++++
 4 files changed, 58 insertions(+), 1 deletion(-)

diff --git a/ChangeLog b/ChangeLog
index 5c8e1c2..65c3ef5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2015-04-14  Petr Machata  <pmachata@redhat.com>
+
+	* configure.ac (HAVE_CXX): New conditional.
+
 2015-03-13  Mark Wielaard  <mjw@redhat.com>
 
 	* configure.ac (ac_cv_c99): Add explicit return.
diff --git a/config/ChangeLog b/config/ChangeLog
index 586ebb0..936f62d 100644
--- a/config/ChangeLog
+++ b/config/ChangeLog
@@ -1,3 +1,9 @@
+2015-04-14  Petr Machata  <pmachata@redhat.com>
+
+	* eu.am (AM_CXXFLAGS, CXXCOMPILE.os): New variables.
+	(%.os: %.c %.o): Create dep-file subdirectory if necessary.
+	(%.os: %.cc %.o): New rule.
+
 2015-03-18  Petr Machata  <pmachata@redhat.com>
 
 	* known-dwarf.awk (comment): Drop all uses of this variable.
diff --git a/config/eu.am b/config/eu.am
index faf8add..f1d290b 100644
--- a/config/eu.am
+++ b/config/eu.am
@@ -1,6 +1,6 @@
 ## Common automake fragments for elfutils subdirectory makefiles.
 ##
-## Copyright (C) 2010, 2014 Red Hat, Inc.
+## Copyright (C) 2010, 2014, 2015 Red Hat, Inc.
 ##
 ## This file is part of elfutils.
 ##
@@ -35,11 +35,17 @@ AM_CFLAGS = -std=gnu99 -Wall -Wshadow -Wformat=2 \
 	    $(if $($(*F)_no_Werror),,-Werror) \
 	    $(if $($(*F)_no_Wunused),,-Wunused -Wextra) \
 	    $($(*F)_CFLAGS)
+AM_CXXFLAGS = -std=gnu++98 -Wall -Wshadow -Wformat=2 \
+	    $(if $($(*F)_no_Werror),,-Werror) \
+	    $(if $($(*F)_no_Wunused),,-Wunused -Wextra) \
+	    $($(*F)_CXXFLAGS)
 
 COMPILE.os = $(filter-out -fprofile-arcs -ftest-coverage, $(COMPILE))
+CXXCOMPILE.os = $(filter-out -fprofile-arcs -ftest-coverage, $(CXXCOMPILE))
 
 %.os: %.c %.o
 if AMDEP
+	test -d $(DEPDIR)/$(*D) || mkdir $(DEPDIR)/$(*D)
 	if $(COMPILE.os) -c -o $@ -fpic -DPIC -DSHARED -MT $@ -MD -MP \
 	  -MF "$(DEPDIR)/$*.Tpo" `test -f '$<' || echo '$(srcdir)/'`$<; \
 	then cat "$(DEPDIR)/$*.Tpo" >> "$(DEPDIR)/$*.Po"; \
@@ -50,6 +56,19 @@ else
 	$(COMPILE.os) -c -o $@ -fpic -DPIC -DSHARED $<
 endif
 
+%.os: %.cc %.o
+if AMDEP
+	test -d $(DEPDIR)/$(*D) || mkdir $(DEPDIR)/$(*D)
+	if $(CXXCOMPILE.os) -c -o $@ -fpic -DPIC -DSHARED -MT $@ -MD -MP \
+	  -MF "$(DEPDIR)/$*.Tpo" `test -f '$<' || echo '$(srcdir)/'`$<; \
+	then cat "$(DEPDIR)/$*.Tpo" >> "$(DEPDIR)/$*.Po"; \
+	     rm -f "$(DEPDIR)/$*.Tpo"; \
+	else rm -f "$(DEPDIR)/$*.Tpo"; exit 1; \
+	fi
+else
+	$(CXXCOMPILE.os) -c -o $@ -fpic -DPIC -DSHARED $<
+endif
+
 CLEANFILES = *.gcno *.gcda
 
 textrel_msg = echo "WARNING: TEXTREL found in '$@'"
diff --git a/configure.ac b/configure.ac
index c4b818d..6d1df60 100644
--- a/configure.ac
+++ b/configure.ac
@@ -71,6 +71,7 @@ AS_IF([test "$use_locks" = yes],
 AH_TEMPLATE([USE_LOCKS], [Defined if libraries should be thread-safe.])
 
 AC_PROG_CC
+AC_PROG_CXX
 AC_PROG_RANLIB
 AC_PROG_YACC
 AM_PROG_LEX
@@ -89,6 +90,33 @@ CFLAGS="$old_CFLAGS"])
 AS_IF([test "x$ac_cv_c99" != xyes],
       AC_MSG_ERROR([gcc with C99 support required]))
 
+AC_LANG_PUSH([C++])
+
+# Above, we check for C++ compiler.  However even if none is available,
+# CXX is set to a non-empty value.  So we need to figure out whether a
+# C++ compiler is actually available.
+
+# We in fact use -std=gnu++98.  Check that the compiler supports this.
+SAVE_CXXFLAGS="$CXXFLAGS"
+CXXFLAGS="$CXXFLAGS -std=gnu++98"
+
+AC_CACHE_CHECK([for C++ compiler that supports -std=gnu++98],
+	       ac_cv_cxx_works,
+[AC_COMPILE_IFELSE([AC_LANG_SOURCE([dnl
+struct foo {
+  int i;
+  explicit foo () : i (0) {}
+  virtual ~foo () {}
+};
+
+struct A { int i; int j; } a = {.i = 1, .j = 2};
+])], ac_cv_cxx_works=yes, ac_cv_cxx_works=no)])
+
+CXXFLAGS="$SAVE_CXXFLAGS"
+AC_LANG_POP()
+
+AM_CONDITIONAL(HAVE_CXX, test "$ac_cv_cxx_works" = yes)
+
 AC_CACHE_CHECK([for __thread support], ac_cv_tls, [dnl
 # Use the same flags that we use for our DSOs, so the test is representative.
 # Some old compiler/linker/libc combinations fail some ways and not others.
-- 
2.1.0

Re: [PATCH 1/2] Enable C++

[Mark Wielaard]

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On Fri, 2015-04-03 at 23:40 +0200, Petr Machata wrote:
> Mark Wielaard <mjw@redhat.com> writes:
> > Why is that mkdir now necessary?
> 
> It's not, but I thought it's a good idea for symmetry.  The reason the
> c++ bits need this mkdir is that we keep that code in a sub-directory,
> and this creates the corresponding sub-directory for the dependency
> tracking helper files.

Aha, ok thanks.

> >> +AC_CACHE_CHECK([for working C++ compiler], ac_cv_cxx_works,
> >> +[AC_LANG_PUSH([C++])
> >> + AC_COMPILE_IFELSE([AC_LANG_SOURCE([dnl
> >> +struct foo {
> >> +  int i;
> >> +  explicit foo () : i (0) {}
> >> +  virtual ~foo () {}
> >> +};])], ac_cv_cxx_works=yes, ac_cv_cxx_works=no)
> >> + AC_LANG_POP()])
> >> +AM_CONDITIONAL(HAVE_CXX, test "$ac_cv_cxx_works" = yes)
> >
> > We require gnu++98 above.
> > Is the explicit enough to make sure the compiler supports C++98?
> 
> Well, this is a C++98 code.  It's of course not enough to test the whole
> C++98--the language is vast.  The reason for that test is that I want to
> make sure we really do have a C++ compiler.  AC_PROG_CXX happily exports
> CXX even if none is available, so we can't use that in conditionals.

I was mostly wondering whether we needed to add an command line argument
like -std=gnu++98 to be sure. But maybe that is all implicit and
standard for all gcc versions anyway.

Cheers,

Mark

Re: [PATCH 1/2] Enable C++

[Petr Machata]

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Mark Wielaard <mjw@redhat.com> writes:

> On Fri, 2015-04-03 at 10:28 +0200, Petr Machata wrote:
>> - Detect C++ compiler in configure, add supporting infrastructure to
>>   eu.am.
>
> Looks good. Two questions below, but not blockers. Just curious.
>
>> index faf8add..f1d290b 100644
>> --- a/config/eu.am
>> +++ b/config/eu.am
>> [...]
>>  %.os: %.c %.o
>>  if AMDEP
>> +	test -d $(DEPDIR)/$(*D) || mkdir $(DEPDIR)/$(*D)
>>  	if $(COMPILE.os) -c -o $@ -fpic -DPIC -DSHARED -MT $@ -MD -MP \
>>  	  -MF "$(DEPDIR)/$*.Tpo" `test -f '$<' || echo '$(srcdir)/'`$<; \
>>  	then cat "$(DEPDIR)/$*.Tpo" >> "$(DEPDIR)/$*.Po"; \
>
> Why is that mkdir now necessary?

It's not, but I thought it's a good idea for symmetry.  The reason the
c++ bits need this mkdir is that we keep that code in a sub-directory,
and this creates the corresponding sub-directory for the dependency
tracking helper files.

>> +AC_CACHE_CHECK([for working C++ compiler], ac_cv_cxx_works,
>> +[AC_LANG_PUSH([C++])
>> + AC_COMPILE_IFELSE([AC_LANG_SOURCE([dnl
>> +struct foo {
>> +  int i;
>> +  explicit foo () : i (0) {}
>> +  virtual ~foo () {}
>> +};])], ac_cv_cxx_works=yes, ac_cv_cxx_works=no)
>> + AC_LANG_POP()])
>> +AM_CONDITIONAL(HAVE_CXX, test "$ac_cv_cxx_works" = yes)
>
> We require gnu++98 above.
> Is the explicit enough to make sure the compiler supports C++98?

Well, this is a C++98 code.  It's of course not enough to test the whole
C++98--the language is vast.  The reason for that test is that I want to
make sure we really do have a C++ compiler.  AC_PROG_CXX happily exports
CXX even if none is available, so we can't use that in conditionals.

Thanks,
Petr

Re: [PATCH 1/2] Enable C++

[Mark Wielaard]

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On Fri, 2015-04-03 at 10:28 +0200, Petr Machata wrote:
> - Detect C++ compiler in configure, add supporting infrastructure to
>   eu.am.

Looks good. Two questions below, but not blockers. Just curious.

> index faf8add..f1d290b 100644
> --- a/config/eu.am
> +++ b/config/eu.am
> [...]
>  %.os: %.c %.o
>  if AMDEP
> +	test -d $(DEPDIR)/$(*D) || mkdir $(DEPDIR)/$(*D)
>  	if $(COMPILE.os) -c -o $@ -fpic -DPIC -DSHARED -MT $@ -MD -MP \
>  	  -MF "$(DEPDIR)/$*.Tpo" `test -f '$<' || echo '$(srcdir)/'`$<; \
>  	then cat "$(DEPDIR)/$*.Tpo" >> "$(DEPDIR)/$*.Po"; \

Why is that mkdir now necessary?

> +AC_CACHE_CHECK([for working C++ compiler], ac_cv_cxx_works,
> +[AC_LANG_PUSH([C++])
> + AC_COMPILE_IFELSE([AC_LANG_SOURCE([dnl
> +struct foo {
> +  int i;
> +  explicit foo () : i (0) {}
> +  virtual ~foo () {}
> +};])], ac_cv_cxx_works=yes, ac_cv_cxx_works=no)
> + AC_LANG_POP()])
> +AM_CONDITIONAL(HAVE_CXX, test "$ac_cv_cxx_works" = yes)

We require gnu++98 above.
Is the explicit enough to make sure the compiler supports C++98?

Thanks,

Mark

[PATCH 1/2] Enable C++

[Petr Machata]

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- Detect C++ compiler in configure, add supporting infrastructure to
  eu.am.

Signed-off-by: Petr Machata <pmachata@redhat.com>
---
 ChangeLog        |  4 ++++
 config/ChangeLog |  6 ++++++
 config/eu.am     | 21 ++++++++++++++++++++-
 configure.ac     | 15 +++++++++++++++
 4 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/ChangeLog b/ChangeLog
index 5c8e1c2..6c6f216 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2015-03-18  Petr Machata  <pmachata@redhat.com>
+
+	* configure.ac (HAVE_CXX): New conditional.
+
 2015-03-13  Mark Wielaard  <mjw@redhat.com>
 
 	* configure.ac (ac_cv_c99): Add explicit return.
diff --git a/config/ChangeLog b/config/ChangeLog
index 586ebb0..32f3c93 100644
--- a/config/ChangeLog
+++ b/config/ChangeLog
@@ -1,3 +1,9 @@
+2015-04-02  Petr Machata  <pmachata@redhat.com>
+
+	* eu.am (AM_CXXFLAGS, CXXCOMPILE.os): New variables.
+	(%.os: %.c %.o): Create dep-file subdirectory if necessary.
+	(%.os: %.cc %.o): New rule.
+
 2015-03-18  Petr Machata  <pmachata@redhat.com>
 
 	* known-dwarf.awk (comment): Drop all uses of this variable.
diff --git a/config/eu.am b/config/eu.am
index faf8add..f1d290b 100644
--- a/config/eu.am
+++ b/config/eu.am
@@ -1,6 +1,6 @@
 ## Common automake fragments for elfutils subdirectory makefiles.
 ##
-## Copyright (C) 2010, 2014 Red Hat, Inc.
+## Copyright (C) 2010, 2014, 2015 Red Hat, Inc.
 ##
 ## This file is part of elfutils.
 ##
@@ -35,11 +35,17 @@ AM_CFLAGS = -std=gnu99 -Wall -Wshadow -Wformat=2 \
 	    $(if $($(*F)_no_Werror),,-Werror) \
 	    $(if $($(*F)_no_Wunused),,-Wunused -Wextra) \
 	    $($(*F)_CFLAGS)
+AM_CXXFLAGS = -std=gnu++98 -Wall -Wshadow -Wformat=2 \
+	    $(if $($(*F)_no_Werror),,-Werror) \
+	    $(if $($(*F)_no_Wunused),,-Wunused -Wextra) \
+	    $($(*F)_CXXFLAGS)
 
 COMPILE.os = $(filter-out -fprofile-arcs -ftest-coverage, $(COMPILE))
+CXXCOMPILE.os = $(filter-out -fprofile-arcs -ftest-coverage, $(CXXCOMPILE))
 
 %.os: %.c %.o
 if AMDEP
+	test -d $(DEPDIR)/$(*D) || mkdir $(DEPDIR)/$(*D)
 	if $(COMPILE.os) -c -o $@ -fpic -DPIC -DSHARED -MT $@ -MD -MP \
 	  -MF "$(DEPDIR)/$*.Tpo" `test -f '$<' || echo '$(srcdir)/'`$<; \
 	then cat "$(DEPDIR)/$*.Tpo" >> "$(DEPDIR)/$*.Po"; \
@@ -50,6 +56,19 @@ else
 	$(COMPILE.os) -c -o $@ -fpic -DPIC -DSHARED $<
 endif
 
+%.os: %.cc %.o
+if AMDEP
+	test -d $(DEPDIR)/$(*D) || mkdir $(DEPDIR)/$(*D)
+	if $(CXXCOMPILE.os) -c -o $@ -fpic -DPIC -DSHARED -MT $@ -MD -MP \
+	  -MF "$(DEPDIR)/$*.Tpo" `test -f '$<' || echo '$(srcdir)/'`$<; \
+	then cat "$(DEPDIR)/$*.Tpo" >> "$(DEPDIR)/$*.Po"; \
+	     rm -f "$(DEPDIR)/$*.Tpo"; \
+	else rm -f "$(DEPDIR)/$*.Tpo"; exit 1; \
+	fi
+else
+	$(CXXCOMPILE.os) -c -o $@ -fpic -DPIC -DSHARED $<
+endif
+
 CLEANFILES = *.gcno *.gcda
 
 textrel_msg = echo "WARNING: TEXTREL found in '$@'"
diff --git a/configure.ac b/configure.ac
index c4b818d..bc40bff 100644
--- a/configure.ac
+++ b/configure.ac
@@ -71,6 +71,7 @@ AS_IF([test "$use_locks" = yes],
 AH_TEMPLATE([USE_LOCKS], [Defined if libraries should be thread-safe.])
 
 AC_PROG_CC
+AC_PROG_CXX
 AC_PROG_RANLIB
 AC_PROG_YACC
 AM_PROG_LEX
@@ -89,6 +90,20 @@ CFLAGS="$old_CFLAGS"])
 AS_IF([test "x$ac_cv_c99" != xyes],
       AC_MSG_ERROR([gcc with C99 support required]))
 
+# Above, we check for C++ compiler.  However even if none is available,
+# CXX is set to a non-empty value.  So we need to figure out whether a
+# C++ compiler is actually available.
+AC_CACHE_CHECK([for working C++ compiler], ac_cv_cxx_works,
+[AC_LANG_PUSH([C++])
+ AC_COMPILE_IFELSE([AC_LANG_SOURCE([dnl
+struct foo {
+  int i;
+  explicit foo () : i (0) {}
+  virtual ~foo () {}
+};])], ac_cv_cxx_works=yes, ac_cv_cxx_works=no)
+ AC_LANG_POP()])
+AM_CONDITIONAL(HAVE_CXX, test "$ac_cv_cxx_works" = yes)
+
 AC_CACHE_CHECK([for __thread support], ac_cv_tls, [dnl
 # Use the same flags that we use for our DSOs, so the test is representative.
 # Some old compiler/linker/libc combinations fail some ways and not others.
-- 
2.1.0