[PATCH] libstdc++: Add workaround for as Error: file number less than one error [PR98708]

[Jakub Jelinek]

Hi!

As mentioned in the PR, since the switch to DWARF5 by default instead of
DWARF4, gcc fails to build when configured against recent binutils.

The problem is that cxx11-ios_failure* is built in separate steps,
-S compilation (with -g -O2) followed by some sed and followed by
-c -g -O2 -g0 assembly.  When gcc is configured against recent binutils
and DWARF5 is the default, we emit .file 0 "..." directive on which the
assembler then fails (unless --gdwarf-5 is passed to it, but we don't want
that generally because on the other side older assemblers don't like -g*
passed to it when invoked on *.s file with compiler generated debug info.

I hope the bug will be fixed soon on the binutils side, but it would be nice
to have a workaround.

The following patch is one of the possibilities, another one is to do that
but add configure check for whether it is needed,
essentially
echo 'int main () { return 0; }' > conftest.c
${CXX} ${CXXFLAGS} -g -O2 -S conftest.c -o conftest.s
${CXX} ${CXXFLAGS} -g -O2 -g0 -c conftest.s -o conftest.o
and if the last command fails, we need that -gno-as-loc-support.
Or yet another option would be I think do a different check, whether
${CXX} ${CXXFLAGS} -g -O2 -S conftest.c -o conftest.s
${CXX} ${CXXFLAGS} -g -O2 -c conftest.s -o conftest.o
works and if yes, don't add the -g0 to cxx11-ios_failure*.s assembly.

I've successfully bootstrapped/regtested this version on x86_64-linux and
i686-linux.

2021-01-18  Jakub Jelinek  <jakub@redhat.com>

	PR debug/98708
	* src/c++11/Makefile.am (cxx11-ios_failure-lt.s, cxx11-ios_failure.s):
	Compile with -gno-as-loc-support.
	* src/c++11/Makefile.in: Regenerated.

--- libstdc++-v3/src/c++11/Makefile.am.jj	2021-01-04 10:26:02.067970728 +0100
+++ libstdc++-v3/src/c++11/Makefile.am	2021-01-17 17:20:58.580262364 +0100
@@ -141,12 +141,12 @@ if ENABLE_DUAL_ABI
 rewrite_ios_failure_typeinfo = sed -e '/^_*_ZTISt13__ios_failure:/,/_ZTVN10__cxxabiv120__si_class_type_infoE/s/_ZTVN10__cxxabiv120__si_class_type_infoE/_ZTVSt19__iosfail_type_info/'
 
 cxx11-ios_failure-lt.s: cxx11-ios_failure.cc
-	$(LTCXXCOMPILE) -S $< -o tmp-cxx11-ios_failure-lt.s
+	$(LTCXXCOMPILE) -gno-as-loc-support -S $< -o tmp-cxx11-ios_failure-lt.s
 	-test -f tmp-cxx11-ios_failure-lt.o && mv -f tmp-cxx11-ios_failure-lt.o tmp-cxx11-ios_failure-lt.s
 	$(rewrite_ios_failure_typeinfo) tmp-$@ > $@
 	-rm -f tmp-$@
 cxx11-ios_failure.s: cxx11-ios_failure.cc
-	$(CXXCOMPILE) -S $< -o tmp-$@
+	$(CXXCOMPILE) -gno-as-loc-support -S $< -o tmp-$@
 	$(rewrite_ios_failure_typeinfo) tmp-$@ > $@
 	-rm -f tmp-$@
 
--- libstdc++-v3/src/c++11/Makefile.in.jj	2020-12-17 02:29:28.734557483 +0100
+++ libstdc++-v3/src/c++11/Makefile.in	2021-01-17 17:21:27.510931383 +0100
@@ -852,12 +852,12 @@ limits.o: limits.cc
 	$(CXXCOMPILE) -fchar8_t -c $<
 
 @ENABLE_DUAL_ABI_TRUE@cxx11-ios_failure-lt.s: cxx11-ios_failure.cc
-@ENABLE_DUAL_ABI_TRUE@	$(LTCXXCOMPILE) -S $< -o tmp-cxx11-ios_failure-lt.s
+@ENABLE_DUAL_ABI_TRUE@	$(LTCXXCOMPILE) -gno-as-loc-support -S $< -o tmp-cxx11-ios_failure-lt.s
 @ENABLE_DUAL_ABI_TRUE@	-test -f tmp-cxx11-ios_failure-lt.o && mv -f tmp-cxx11-ios_failure-lt.o tmp-cxx11-ios_failure-lt.s
 @ENABLE_DUAL_ABI_TRUE@	$(rewrite_ios_failure_typeinfo) tmp-$@ > $@
 @ENABLE_DUAL_ABI_TRUE@	-rm -f tmp-$@
 @ENABLE_DUAL_ABI_TRUE@cxx11-ios_failure.s: cxx11-ios_failure.cc
-@ENABLE_DUAL_ABI_TRUE@	$(CXXCOMPILE) -S $< -o tmp-$@
+@ENABLE_DUAL_ABI_TRUE@	$(CXXCOMPILE) -gno-as-loc-support -S $< -o tmp-$@
 @ENABLE_DUAL_ABI_TRUE@	$(rewrite_ios_failure_typeinfo) tmp-$@ > $@
 @ENABLE_DUAL_ABI_TRUE@	-rm -f tmp-$@
 

	Jakub