From d7153c4ac333c9127c18efcf184607d368bb142d Mon Sep 17 00:00:00 2001 From: Alan Modra Date: Thu, 27 Apr 2017 11:08:14 +0930 Subject: [PATCH] Edit .eh_frame symbols Experimental support for moving symbols defined in .eh_frame as their CIEs/FDEs are edited or merged. * elf-bfd.h (struct eh_cie_fde): Add aug_str_len and aug_data_len. (_bfd_elf_adjust_eh_frame_global_symbol): Declare. * elf-eh-frame.c (_bfd_elf_parse_eh_frame): Set aug_str_len and aug_data_len. (offset_adjust): New function. (_bfd_elf_adjust_eh_frame_global_symbol): Likewise. (adjust_eh_frame_local_symbols): Likewise. (_bfd_elf_discard_section_eh_frame): Call adjust_eh_frame_local_symbols after changing anything. Return true if anything changed. * elflink.c (bfd_elf_discard_info): If .eh_frame changed, call _bfd_elf_adjust_eh_frame_global_symbol for globals. --- bfd/ChangeLog | 14 +++++ bfd/elf-bfd.h | 10 +++- bfd/elf-eh-frame.c | 154 ++++++++++++++++++++++++++++++++++++++++++++++++++++- bfd/elflink.c | 10 +++- 4 files changed, 185 insertions(+), 3 deletions(-) diff --git a/bfd/ChangeLog b/bfd/ChangeLog index c870cc7..0f08ddd 100644 --- a/bfd/ChangeLog +++ b/bfd/ChangeLog @@ -1,5 +1,19 @@ 2017-04-27 Alan Modra + * elf-bfd.h (struct eh_cie_fde): Add aug_str_len and aug_data_len. + (_bfd_elf_adjust_eh_frame_global_symbol): Declare. + * elf-eh-frame.c (_bfd_elf_parse_eh_frame): Set aug_str_len and + aug_data_len. + (offset_adjust): New function. + (_bfd_elf_adjust_eh_frame_global_symbol): Likewise. + (adjust_eh_frame_local_symbols): Likewise. + (_bfd_elf_discard_section_eh_frame): Call adjust_eh_frame_local_symbols + after changing anything. Return true if anything changed. + * elflink.c (bfd_elf_discard_info): If .eh_frame changed, call + _bfd_elf_adjust_eh_frame_global_symbol for globals. + +2017-04-27 Alan Modra + * elflink.c (_bfd_elf_link_hash_hide_symbol): Clear dynstr_index when force_local. diff --git a/bfd/elf-bfd.h b/bfd/elf-bfd.h index 2649939..bff6abc 100644 --- a/bfd/elf-bfd.h +++ b/bfd/elf-bfd.h @@ -326,6 +326,12 @@ struct eh_cie_fde or 0 if the CIE doesn't have any. */ unsigned int personality_offset : 8; + /* Length of augmentation. aug_str_len is the length of the + string including null terminator. aug_data_len is the length + of the rest up to the initial insns. */ + unsigned int aug_str_len : 3; + unsigned int aug_data_len : 5; + /* True if we have marked relocations associated with this CIE. */ unsigned int gc_mark : 1; @@ -354,7 +360,7 @@ struct eh_cie_fde unsigned int merged : 1; /* Unused bits. */ - unsigned int pad1 : 17; + unsigned int pad1 : 9; } cie; } u; unsigned int reloc_index; @@ -2180,6 +2186,8 @@ extern bfd_boolean _bfd_elf_end_eh_frame_parsing extern bfd_boolean _bfd_elf_discard_section_eh_frame (bfd *, struct bfd_link_info *, asection *, bfd_boolean (*) (bfd_vma, void *), struct elf_reloc_cookie *); +extern bfd_boolean _bfd_elf_adjust_eh_frame_global_symbol + (struct elf_link_hash_entry *, void *); extern bfd_boolean _bfd_elf_discard_section_eh_frame_hdr (bfd *, struct bfd_link_info *); extern bfd_vma _bfd_elf_eh_frame_section_offset diff --git a/bfd/elf-eh-frame.c b/bfd/elf-eh-frame.c index 1743823..1af6f30 100644 --- a/bfd/elf-eh-frame.c +++ b/bfd/elf-eh-frame.c @@ -757,6 +757,7 @@ _bfd_elf_parse_eh_frame (bfd *abfd, struct bfd_link_info *info, strcpy (cie->augmentation, (char *) buf); buf = (bfd_byte *) strchr ((char *) buf, '\0') + 1; + this_inf->u.cie.aug_str_len = buf - start - 1; ENSURE_NO_RELOCS (buf); if (buf[0] == 'e' && buf[1] == 'h') { @@ -845,6 +846,8 @@ _bfd_elf_parse_eh_frame (bfd *abfd, struct bfd_link_info *info, goto free_no_table; } } + this_inf->u.cie.aug_data_len + = buf - start - 1 - this_inf->u.cie.aug_str_len; /* For shared libraries, try to get rid of as many RELATIVE relocs as possible. */ @@ -1327,6 +1330,143 @@ find_merged_cie (bfd *abfd, struct bfd_link_info *info, asection *sec, return new_cie->cie_inf; } +/* For a given OFFSET in SEC, return the delta to the new location + after .eh_frame editing. */ + +static bfd_signed_vma +offset_adjust (bfd_vma offset, asection *sec) +{ + struct eh_frame_sec_info *sec_info + = (struct eh_frame_sec_info *) elf_section_data (sec)->sec_info; + unsigned int lo, hi, mid; + struct eh_cie_fde *ent; + bfd_signed_vma delta; + + lo = 0; + hi = sec_info->count; + if (hi == 0) + return 0; + + while (lo < hi) + { + mid = (lo + hi) / 2; + ent = &sec_info->entry[mid]; + if (offset < ent->offset) + hi = mid; + else if (mid + 1 >= hi) + break; + else if (offset >= ent[1].offset) + lo = mid + 1; + else + break; + } + + if (!ent->removed) + delta = (bfd_vma) ent->new_offset - (bfd_vma) ent->offset; + else if (ent->cie && ent->u.cie.merged) + { + struct eh_cie_fde *cie = ent->u.cie.u.merged_with; + delta = ((bfd_vma) cie->new_offset + cie->u.cie.u.sec->output_offset + - (bfd_vma) ent->offset - sec->output_offset); + } + else + { + /* Is putting the symbol on the next entry best for a deleted + CIE/FDE? */ + struct eh_cie_fde *last = sec_info->entry + sec_info->count; + delta = ((bfd_vma) next_cie_fde_offset (ent, last, sec) + - (bfd_vma) ent->offset); + return delta; + } + + /* Account for editing within this CIE/FDE. */ + offset -= ent->offset; + if (ent->cie) + { + unsigned int extra + = ent->add_augmentation_size + ent->u.cie.add_fde_encoding; + if (extra == 0 + || offset <= 9u + ent->u.cie.aug_str_len) + return delta; + delta += extra; + if (offset <= 9u + ent->u.cie.aug_str_len + ent->u.cie.aug_data_len) + return delta; + delta += extra; + } + else + { + unsigned int ptr_size, width, extra = ent->add_augmentation_size; + if (offset <= 12 || extra == 0) + return delta; + ptr_size = (get_elf_backend_data (sec->owner) + ->elf_backend_eh_frame_address_size (sec->owner, sec)); + width = get_DW_EH_PE_width (ent->fde_encoding, ptr_size); + if (offset <= 8 + 2 * width) + return delta; + delta += extra; + } + + return delta; +} + +/* Adjust a global symbol defined in .eh_frame, so that it stays + relative to its original CIE/FDE. It is assumed that a symbol + defined at the beginning of a CIE/FDE belongs to that CIE/FDE + rather than marking the end of the previous CIE/FDE. This matters + when a CIE is merged with a previous CIE, since the symbol is + moved to the merged CIE. */ + +bfd_boolean +_bfd_elf_adjust_eh_frame_global_symbol (struct elf_link_hash_entry *h, + void *arg ATTRIBUTE_UNUSED) +{ + asection *sym_sec; + bfd_signed_vma delta; + + if (h->root.type != bfd_link_hash_defined + && h->root.type != bfd_link_hash_defweak) + return TRUE; + + sym_sec = h->root.u.def.section; + if (sym_sec->sec_info_type != SEC_INFO_TYPE_EH_FRAME + || elf_section_data (sym_sec)->sec_info == NULL) + return TRUE; + + delta = offset_adjust (h->root.u.def.value, sym_sec); + h->root.u.def.value += delta; + + return TRUE; +} + +/* The same for all local symbols defined in .eh_frame. Returns true + if any symbol was changed. */ + +static int +adjust_eh_frame_local_symbols (asection *sec, + struct elf_reloc_cookie *cookie) +{ + unsigned int shndx; + Elf_Internal_Sym *sym; + Elf_Internal_Sym *end_sym; + int adjusted = 0; + + shndx = elf_section_data (sec)->this_idx; + end_sym = cookie->locsyms + cookie->locsymcount; + for (sym = cookie->locsyms + 1; sym < end_sym; ++sym) + if (sym->st_info <= ELF_ST_INFO (STB_LOCAL, STT_OBJECT) + && sym->st_shndx == shndx) + { + bfd_signed_vma delta = offset_adjust (sym->st_value, sec); + + if (delta != 0) + { + adjusted = 1; + sym->st_value += delta; + } + } + return adjusted; +} + /* This function is called for each input file before the .eh_frame section is relocated. It discards duplicate CIEs and FDEs for discarded functions. The function returns TRUE iff any entries have been @@ -1342,6 +1482,7 @@ _bfd_elf_discard_section_eh_frame struct eh_frame_sec_info *sec_info; struct eh_frame_hdr_info *hdr_info; unsigned int ptr_size, offset, eh_alignment; + int changed; if (sec->sec_info_type != SEC_INFO_TYPE_EH_FRAME) return FALSE; @@ -1428,6 +1569,7 @@ _bfd_elf_discard_section_eh_frame last FDE instead. For other FDEs we align according to their encoding, in order to align FDE address range entries naturally. */ offset = 0; + changed = 0; for (ent = sec_info->entry; ent < sec_info->entry + sec_info->count; ++ent) if (!ent->removed) { @@ -1447,6 +1589,8 @@ _bfd_elf_discard_section_eh_frame } offset = (offset + eh_alignment - 1) & -eh_alignment; ent->new_offset = offset; + if (ent->new_offset != ent->offset) + changed = 1; offset += size_of_output_cie_fde (ent); } @@ -1463,7 +1607,15 @@ _bfd_elf_discard_section_eh_frame offset = (offset + eh_alignment - 1) & -eh_alignment; sec->rawsize = sec->size; sec->size = offset; - return offset != sec->rawsize; + if (sec->size != sec->rawsize) + changed = 1; + + if (changed && adjust_eh_frame_local_symbols (sec, cookie)) + { + Elf_Internal_Shdr *symtab_hdr = &elf_tdata (abfd)->symtab_hdr; + symtab_hdr->contents = (unsigned char *) cookie->locsyms; + } + return changed; } /* This function is called for .eh_frame_hdr section after diff --git a/bfd/elflink.c b/bfd/elflink.c index 59300b7..4af4b1c 100644 --- a/bfd/elflink.c +++ b/bfd/elflink.c @@ -13807,6 +13807,7 @@ bfd_elf_discard_info (bfd *output_bfd, struct bfd_link_info *info) if (o != NULL) { asection *i; + int eh_changed = 0; for (i = o->map_head.s; i != NULL; i = i->map_head.s) { @@ -13824,10 +13825,17 @@ bfd_elf_discard_info (bfd *output_bfd, struct bfd_link_info *info) if (_bfd_elf_discard_section_eh_frame (abfd, info, i, bfd_elf_reloc_symbol_deleted_p, &cookie)) - changed = 1; + { + eh_changed = 1; + if (i->size != i->rawsize) + changed = 1; + } fini_reloc_cookie_for_section (&cookie, i); } + if (eh_changed) + elf_link_hash_traverse (elf_hash_table (info), + _bfd_elf_adjust_eh_frame_global_symbol, NULL); } for (abfd = info->input_bfds; abfd != NULL; abfd = abfd->link.next) -- 2.7.4