On Fri, Nov 6, 2020 at 3:22 PM Jeff Law <l...@redhat.com> wrote: > > > On 11/5/20 7:34 AM, H.J. Lu via Gcc-patches wrote: > > On Thu, Nov 5, 2020 at 3:37 AM Jozef Lawrynowicz > > <joze...@mittosystems.com> wrote: > >> On Thu, Nov 05, 2020 at 06:21:21AM -0500, Hans-Peter Nilsson wrote: > >>> On Wed, 4 Nov 2020, H.J. Lu wrote: > >>>> .retain is ill-defined. For example, > >>>> > >>>> [hjl@gnu-cfl-2 gcc]$ cat /tmp/x.c > >>>> static int xyzzy __attribute__((__used__)); > >>>> [hjl@gnu-cfl-2 gcc]$ ./xgcc -B./ -S /tmp/x.c -fcommon > >>>> [hjl@gnu-cfl-2 gcc]$ cat x.s > >>>> .file "x.c" > >>>> .text > >>>> .retain xyzzy <<<<<<<<< What does it do? > >>>> .local xyzzy > >>>> .comm xyzzy,4,4 > >>>> .ident "GCC: (GNU) 11.0.0 20201103 (experimental)" > >>>> .section .note.GNU-stack,"",@progbits > >>>> [hjl@gnu-cfl-2 gcc]$ > >>> To answer that question: it's up to the assembler, but for ELF > >>> and SHF_GNU_RETAIN, it seems obvious it'd tell the assembler to > >>> set SHF_GNU_RETAIN for the section where the symbol ends up. > >>> We both know this isn't rocket science with binutils. > >> Indeed, and my patch handles it trivially: > >> https://sourceware.org/pipermail/binutils/2020-November/113993.html > >> > >> +void > >> +obj_elf_retain (int arg ATTRIBUTE_UNUSED) > >> .... snip .... > >> + sym = get_sym_from_input_line_and_check (); > >> + symbol_get_obj (sym)->retain = 1; > >> > >> @@ -2624,6 +2704,9 @@ elf_frob_symbol (symbolS *symp, int *puntp) > >> } > >> } > >> > >> + if (symbol_get_obj (symp)->retain) > >> + elf_section_flags (S_GET_SEGMENT (symp)) |= SHF_GNU_RETAIN; > >> + > >> /* Double check weak symbols. */ > >> if (S_IS_WEAK (symp)) > >> { > >> > >> We could check that the symbol named in the .retain directive has > >> already been defined, however this isn't compatible with GCC > >> mark_decl_preserved handling, since mark_decl_preserved is called > >> emitted before the local symbols are defined in the assembly output > >> file. > >> > >> GAS should at least validate that the symbol named in the .retain > >> directive does end up as a symbol though. > >> > > Don't add .retain. > > Why? I don't see why you find it so objectionable. >
An ELF symbol directive should operate on symbol table: http://www.sco.com/developers/gabi/latest/ch4.symtab.html not the section flags where the symbol is defined. -- H.J.
