On Mon, Mar 9, 2020 at 2:30 AM Martin Liška <mli...@suse.cz> wrote: > > Hi. > > With change of -fno-common default for GCC 10 we're facing serious > problem with LTO where one can't distinguish in between global symbols > and variables based on the output of nm: > https://sourceware.org/bugzilla/show_bug.cgi?id=25355 > > $ cat nm.c > char nm_test_var; > > $ gcc-9 nm.c -c -fno-common > $ nm nm.o > 0000000000000000 B nm_test_var > > $ gcc-9 nm.c -c -fno-common -flto > $ nm nm.o > 00000000 T nm_test_var > > H.J. decided to implement quite heavy solution which is about usage of > lto-wrapper > that takes a LTO object file and makes a final assembly file. The file is then > utilized with nm. That has some disadvantages: > > - it's slow - using nm x.a can take very long time > - way of finding lto-wrapper is quite hard-coded to location of LTO plugin > - we face issues with multiple final object files: > https://sourceware.org/bugzilla/show_bug.cgi?id=25640 > > That said, I'm suggesting to expect LTO plugin API to tell binutils whether > a symbol is variable or function. That should help us to mark global variables > with "D" in nm output. > > I would like to note that even with -fcommon, the nm output for LTO bytecode > is far > from perfect: > > $ cat bss.c > int global_zero; > int global_one = 1; > > $ gcc-9 bss.c -c -flto > $ nm bss.o > 00000000 T global_one > 00000000 C global_zero > > I believe in this case we can mark both symbols with D as a reasonable guess. > > Thoughts? > Martin > > gcc/ChangeLog: > > 2020-03-09 Martin Liska <mli...@suse.cz> > > * lto-streamer-out.c (write_symbol): Stream > symbol type. > > include/ChangeLog: > > 2020-03-09 Martin Liska <mli...@suse.cz> > > * lto-symtab.h (enum gcc_plugin_symbol_type): New. > * plugin-api.h (struct ld_plugin_symbol): New member > symbols_type. > (enum ld_plugin_symbol_type): New. > (enum ld_plugin_tag): Add new tag LDPT_GET_SYMBOLS_V4. > > lto-plugin/ChangeLog: > > 2020-03-09 Martin Liska <mli...@suse.cz> > > * lto-plugin.c (parse_table_entry): Parse symbol type. > --- > gcc/lto-streamer-out.c | 2 ++ > include/lto-symtab.h | 7 +++++++ > include/plugin-api.h | 13 ++++++++++++- > lto-plugin/lto-plugin.c | 12 ++++++++++++ > 4 files changed, 33 insertions(+), 1 deletion(-) > >
We nee to support different variables, like TLS, data and bss variables. -- H.J.
