On 10 Oct 19:00, Jakub Jelinek wrote: > On Fri, Oct 10, 2014 at 09:51:02AM -0700, Cary Coutant wrote: > > The linker already has a --strip-lto-sections option, and it's on by > > default. I'll approve a patch that modifies gold to recognize > > .gnu.offload_lto.* sections as part of --strip-lto-sections. > > > > Really, though, you should be setting the SHF_EXCLUDE bit on these > > sections. Do that and no special-casing will be necessary. > > For that I guess > lhd_begin_section > would need to replace: > section = get_section (name, SECTION_DEBUG, NULL); > with: > section = get_section (name, SECTION_DEBUG | SECTION_EXCLUDE, NULL); > either just for the .gnu.offload_lto prefixed section, or all. > The question is what will old assemblers and/or linkers do with that, and > if there are any that support linker plugins, but not SHF_EXCLUDE.
I've tried to set SECTION_EXCLUDE bit with as+ld version 2.20.51 and got a lot of warnings like: /tmp/ccg7P7iS.s:2: Warning: entity size for SHF_MERGE not specified /tmp/ccg7P7iS.s:2: Warning: group name for SHF_GROUP not specified as: /tmp/ccKFKXfc.o: warning: sh_link not set for section `.gnu.lto_main.11d9780ff2ebf166' /usr/bin/ld: /tmp/ccKFKXfc.o: warning: sh_link not set for section `.gnu.lto_main.11d9780ff2ebf166' I think, it can be placed under such ifdef: #if defined (HAVE_SECTION_EXCLUDE) && HAVE_SECTION_EXCLUDE == 1 section = get_section (name, SECTION_DEBUG | SECTION_EXCLUDE, NULL); #else section = get_section (name, SECTION_DEBUG, NULL); #endif Currently there is HAVE_GAS_SECTION_EXCLUDE implemented in gcc/configure.ac, and HAVE_SECTION_EXCLUDE can use it + check a version of the linker. As for old assemblers and/or linkers, which doesn't support SHF_EXCLUDE: On 10 Oct 08:53, Jakub Jelinek wrote: > Anyway, can you do the partial linker script for the bfd linker (is there > a way to determine from the linker plugin API if it is gold or bfd ld?), and > for gold for the time being perhaps strip the sections in lto-wrapper? and > feed the ET_REL objects with the sections stripped back to the linker > through the plugin API? Yes, it's possible to determine the versions of gold and ld.bfd from the plugin (plugin-api.h:ld_plugin_tag). But the problem is not only with plugins. If linker plugin in disabled, collect2 runs lto-wrapper directly to compile offload_lto sections and/or to perform usual LTO: https://gcc.gnu.org/wiki/Offloading#Compilation_without_-flto_and_without_linker_plugin And if -flto is absent, but offload_lto sections were emitted, the final binary will contain them. Perhaps, collect2 could execute and parse `ld --version` to determine whether it supports SHF_EXCLUDE. Then, we need somehow pass this information from plugin or collect2 to lto-wrapper. Maybe using an option like --strip-offload-sections, but currently lto-wrapper doesn't have its own options. And finally, under this option lto-wrapper will execute `objcopy --remove-section=<offload_lto>` and return stripped objects back to the linker or to collect2. So, should I implement this stuff, or maybe just leave offload_lto sections in the case of old binutils? :) Thanks, -- Ilya
