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Re: [C++] Fix PR bootstrap/81926
- From: Richard Biener <richard dot guenther at gmail dot com>
- To: gcc-patches at gcc dot gnu dot org,Eric Botcazou <ebotcazou at adacore dot com>
- Date: Sat, 02 Sep 2017 16:33:16 +0200
- Subject: Re: [C++] Fix PR bootstrap/81926
- Authentication-results: sourceware.org; auth=none
- References: <4078981.6jQ9KEkrUD@polaris>
On September 2, 2017 1:01:11 PM GMT+02:00, Eric Botcazou <ebotcazou@adacore.com> wrote:
>Hi,
>
>this is the bootstrap failure reported for the 7 branch on
>SPARC64/Solaris:
>
>Comparing stages 2 and 3
>Bootstrap comparison failure!
>gcc/go/parse.o differs
>make[2]: *** [compare] Error 1
>
>On Solaris, the bootstrap is usually an old-style bootstrap, meaning
>that the
>debug info is generated during stage2 & stage3 so the comparison also
>involves
>the debug info, unlike on Linux. This can be emulated on Linux by
>configuring
>--with-build-config=no and indeed you get the comparison failure there
>too:
>
>Target: x86_64-suse-linux
>Configured with: /home/eric/svn/gcc-7.2.0/configure
>--build=x86_64-suse-linux
>--prefix=/home/eric/install/gcc-7.2.0 --enable-languages=c,c++,go
>--enable-
>__cxa_atexit --disable-nls --with-build-config=no
>Thread model: posix
>gcc version 7.2.0 (GCC)
>
>make[3]: Leaving directory '/home/eric/build/gcc-7.2.0'
>Comparing stages 2 and 3
>Bootstrap comparison failure!
>gcc/go/parse.o differs
>Makefile:24421: recipe for target 'compare' failed
>make[2]: *** [compare] Error 1
>
>The difference is:
>
>35 .debug_info 0016367a 0000000000000000 0000000000000000 0001faf8
> 2**0
> CONTENTS, RELOC, READONLY, DEBUGGING
>
>35 .debug_info 00163670 0000000000000000 0000000000000000 0001faf8
> 2**0
> CONTENTS, RELOC, READONLY, DEBUGGING
>
> .byte 0 ! end of children of DIE 0x161dbc
> .byte 0 ! end of children of DIE 0x161d9c
> .byte 0 ! end of children of DIE 0x161d5b
>- .byte 0xf2,0x1 ! uleb128 0xf2; (DIE (0x161dd2)
>DW_TAG_ptr_to_member_type)
>- .uaword 0x10445d ! DW_AT_containing_type
>- .uaword 0x14806e ! DW_AT_type
>- .byte 0xa5,0x1 ! uleb128 0xa5; (DIE (0x161ddc)
>DW_TAG_subprogram)
>+ .byte 0xa5,0x1 ! uleb128 0xa5; (DIE (0x161dd2)
>DW_TAG_subprogram)
> .uaword 0x146733 ! DW_AT_abstract_origin
>
>It's a garbage collection issue similar to
> https://gcc.gnu.org/ml/gcc-patches/2016-10/msg00541.html
>but for build_offset_type instead of build_complex_type.
>
>It's called from the get_debug_type langhook in C++:
>
>tree
>cp_get_debug_type (const_tree type)
>{
> if (TYPE_PTRMEMFUNC_P (type) && !typedef_variant_p (type))
> return build_offset_type (TYPE_PTRMEMFUNC_OBJECT_TYPE (type),
> TREE_TYPE (TYPE_PTRMEMFUNC_FN_TYPE (type)));
>
> return NULL_TREE;
>}
>
>Since the OFFSET_TYPEs created there are not attached to any GC root,
>they are
>swept by every collection, meaning that the contents of the debug info
>depends
>on the actual collection points.
>
>The proposed fix is to build OFFSET_TYPEs manually instead. As
>witnessed by
>the change to g++.dg/debug/dwarf2/ref-3.C, this generates more DIEs in
>the
>debug info, but DW_TAG_ptr_to_member_type DIEs only contain 10 bytes.
A solution would be to put them into a global GCed pointer-map or vector, freeing that at free-lang-data time.
Richard.
>Bootstrapped on x86-64/Linux & SPARC64/Solaris, OK for mainline and 7
>branch?
>
>
>2017-09-02 Eric Botcazou <ebotcazou@adacore.com>
>
> PR bootstrap/81926
> * cp-objcp-common.c: Include stor-layout.h.
> (cp_get_debug_type): Build OFFSET_TYPEs manually.
>
>
>2017-09-02 Eric Botcazou <ebotcazou@adacore.com>
>
> * g++.dg/debug/dwarf2/ref-3.C: Adjust DW_TAG_ptr_to_member_type count.