https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96385
--- Comment #13 from Richard Biener <rguenth at gcc dot gnu.org> --- (In reply to Richard Biener from comment #12) > (In reply to H.J. Lu from comment #10) > > (In reply to H.J. Lu from comment #8) > > > The original pr26324a.o debug info contains reference to xxx. But > > > reference > > > to xxx has been removed by LTO. simple_object_copy_lto_debug_sections > > > fails > > > to remove the un-referenced symbol, xxx, from symbol table. > > > > The alternative is to ask linker to handle it: > > > > https://sourceware.org/pipermail/binutils/2020-July/112673.html > > The bug is we create the reference in the first place. Oh, I see. So we had multiple choices for "pruning" symbols from the symbol table during simple_object_copy_lto_debug_sections and factoring in HP-UX and Solaris (sic!...) emptying UND symbol names didn't work out. So we do now if (discard) { /* Make discarded symbols undefined and unnamed in case it is local. */ int bind = ELF_ST_BIND (*st_info); int other = STV_DEFAULT; if (bind == STB_LOCAL) { /* Make discarded local symbols unnamed and defined in the first prevailing section. */ ELF_SET_FIELD (type_functions, ei_class, Sym, ent, st_name, Elf_Word, 0); ELF_SET_FIELD (type_functions, ei_class, Sym, ent, st_shndx, Elf_Half, sh_map[first_shndx]); } else { /* Make discarded global symbols hidden weak undefined and sharing a name of a prevailing symbol. */ bind = STB_WEAK; other = STV_HIDDEN; ELF_SET_FIELD (type_functions, ei_class, Sym, ent, st_name, Elf_Word, prevailing_name_idx); ELF_SET_FIELD (type_functions, ei_class, Sym, ent, st_shndx, Elf_Half, SHN_UNDEF); } *st_other = other; *st_info = ELF_ST_INFO (bind, STT_NOTYPE); ELF_SET_FIELD (type_functions, ei_class, Sym, ent, st_value, Elf_Addr, 0); ELF_SET_FIELD (type_functions, ei_class, Sym, ent, st_size, Elf_Word, 0); } but somehow the else path isn't triggered(?). Note that all we try to avoid is the need to rewrite relocation sections if we really would prune symbols rather than NULL-ifying them somehow. You can trace history as to how the above code morphed with various bugs in the past... Hmm, we don't treat SHN_UNDEF any special here - I guess we could at most make all of them WEAK ... the following should address this. diff --git a/libiberty/simple-object-elf.c b/libiberty/simple-object-elf.c index c62d5bba551..7c9d492f6a4 100644 --- a/libiberty/simple-object-elf.c +++ b/libiberty/simple-object-elf.c @@ -1467,6 +1467,11 @@ simple_object_elf_copy_lto_debug_sections (simple_object_read *sobj, && st_shndx < shnum && pfnret[st_shndx - 1] == -1) discard = 1; + /* We also need to remove global UNDEFs which can + cause link fails later. */ + else if (st_shndx == SHN_UNDEF + && ELF_ST_BIND (*st_info) == STB_GLOBAL) + discard = 1; if (discard) {
