[PATCH] Introduce -nolibstdc++ option

[Alexandre Oliva <oliva@adacore.com>]

Using g++ to link without libstdc++, as in g++.dg/abi/pure-virtual1.C,
is error prone, because there's no way to tell g++ to drop libstdc++
without also dropping libc and any other libraries that the target
implicitly links in.

This has often led to the need for manual adjustments to this
testcase.

I figured adding support for -nolibstdc++, even though redundant,
makes some sense.  One could presumably use gcc rather than g++ for
linking, for the same effect, but sometimes changing the link command
is harder than adding an option, as in our testsuite.

Regstrapped on x86_64-linux-gnu, also tested with a cross to
aarch64-rtems6.  Ok to install?


for  gcc/ChangeLog

	* common.opt (nolibstdc++): New.
	* doc/invoke.texi (-nolibstdc++): Document it.

for  gcc/cp/ChangeLog

	* g++spec.c (lang_specific_driver): Implement -nolibstdc++.

for  gcc/testsuite/ChangeLog

	* g++.dg/abi/pure-virtual1.C: Use -nolibstdc++.
---
 gcc/common.opt                           |    3 +++
 gcc/cp/g++spec.cc                        |    1 +
 gcc/doc/invoke.texi                      |    6 +++++-
 gcc/testsuite/g++.dg/abi/pure-virtual1.C |    2 +-
 4 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/gcc/common.opt b/gcc/common.opt
index 32917aafcaec1..e00c6fc2fb098 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -3456,6 +3456,9 @@ Driver
 nolibc
 Driver
 
+nolibstdc++
+Driver
+
 nostdlib
 Driver
 
diff --git a/gcc/cp/g++spec.cc b/gcc/cp/g++spec.cc
index 8174d652776b1..539e6ca089d85 100644
--- a/gcc/cp/g++spec.cc
+++ b/gcc/cp/g++spec.cc
@@ -160,6 +160,7 @@ lang_specific_driver (struct cl_decoded_option **in_decoded_options,
 	{
 	case OPT_nostdlib:
 	case OPT_nodefaultlibs:
+	case OPT_nolibstdc__:
 	  library = -1;
 	  break;
 
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 50f57877477bc..469b6d97e0dfa 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -652,7 +652,7 @@ Objective-C and Objective-C++ Dialects}.
 @item Linker Options
 @xref{Link Options,,Options for Linking}.
 @gccoptlist{@var{object-file-name}  -fuse-ld=@var{linker}  -l@var{library} @gol
--nostartfiles  -nodefaultlibs  -nolibc  -nostdlib @gol
+-nostartfiles  -nodefaultlibs  -nolibc  -nolibstdc++  -nostdlib @gol
 -e @var{entry}  --entry=@var{entry} @gol
 -pie  -pthread  -r  -rdynamic @gol
 -s  -static  -static-pie  -static-libgcc  -static-libstdc++ @gol
@@ -16787,6 +16787,10 @@ absence of a C library is assumed, for example @option{-lpthread} or
 @option{-lm} in some configurations.  This is intended for bare-board
 targets when there is indeed no C library available.
 
+@item -nolibstdc++
+@opindex nolibstdc++
+Do not link with standard C++ libraries implicitly.
+
 @item -nostdlib
 @opindex nostdlib
 Do not use the standard system startup files or libraries when linking.
diff --git a/gcc/testsuite/g++.dg/abi/pure-virtual1.C b/gcc/testsuite/g++.dg/abi/pure-virtual1.C
index 538e2cb097a0d..889c33e4952f4 100644
--- a/gcc/testsuite/g++.dg/abi/pure-virtual1.C
+++ b/gcc/testsuite/g++.dg/abi/pure-virtual1.C
@@ -1,7 +1,7 @@
 // Test that we don't need libsupc++ just for __cxa_pure_virtual.
 // { dg-do link }
 // { dg-require-weak }
-// { dg-additional-options "-fno-rtti -nodefaultlibs -lc" }
+// { dg-additional-options "-fno-rtti -nolibstdc++" }
 // { dg-additional-options "-Wl,-undefined,dynamic_lookup" { target *-*-darwin* } }
 // { dg-xfail-if "AIX weak" { powerpc-ibm-aix* } }
 

-- 
Alexandre Oliva, happy hacker                https://FSFLA.org/blogs/lxo/
   Free Software Activist                       GNU Toolchain Engineer
Disinformation flourishes because many people care deeply about injustice
but very few check the facts.  Ask me about <https://stallmansupport.org>