objcopy: restore behaviour required by GCC's build
In r339350 filter_reloc() was removed, to fix the case of stripping statically linked binaries with relocations (which may come from ifunc use, for example). As a side effect this changed the behaviour when stripping object files - the output was broken both before and after r339350, in different ways. Unfortunately GCC's build process relies on the previous behaviour, so: - Revert r339350, restoring filter_reloc(). - Fix an unitialized variable use (commited as r3638 in ELF Tool Chain). - Change filter_reloc() to omit relocations referencing removed symbols, while retaining relocations with no symbol reference. - Retain the entire relocation section if it references the dynamic symbol table (fix from kaiw in D17596). PR: 232176 Reported by: antoine Reviewed by: kaiw MFC with: r339350 Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D17596
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@ -39,6 +39,7 @@ ELFTC_VCSID("$Id: sections.c 3443 2016-04-15 18:57:54Z kaiwang27 $");
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static void add_gnu_debuglink(struct elfcopy *ecp);
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static uint32_t calc_crc32(const char *p, size_t len, uint32_t crc);
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static void check_section_rename(struct elfcopy *ecp, struct section *s);
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static void filter_reloc(struct elfcopy *ecp, struct section *s);
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static int get_section_flags(struct elfcopy *ecp, const char *name);
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static void insert_sections(struct elfcopy *ecp);
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static void insert_to_strtab(struct section *t, const char *s);
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@ -572,6 +573,14 @@ copy_content(struct elfcopy *ecp)
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strcmp(s->name, ".shstrtab") == 0)
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continue;
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/*
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* If strip action is STRIP_ALL, relocation info need
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* to be stripped. Skip filtering otherwisw.
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*/
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if (ecp->strip == STRIP_ALL &&
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(s->type == SHT_REL || s->type == SHT_RELA))
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filter_reloc(ecp, s);
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/*
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* The section indices in the SHT_GROUP section needs
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* to be updated since we might have stripped some
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@ -664,6 +673,140 @@ update_section_group(struct elfcopy *ecp, struct section *s)
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s->nocopy = 1;
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}
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/*
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* Filter relocation entries, only keep those entries whose
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* symbol is in the keep list.
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*/
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static void
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filter_reloc(struct elfcopy *ecp, struct section *s)
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{
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const char *name;
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GElf_Shdr ish;
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GElf_Rel rel;
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GElf_Rela rela;
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Elf32_Rel *rel32;
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Elf64_Rel *rel64;
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Elf32_Rela *rela32;
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Elf64_Rela *rela64;
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Elf_Data *id;
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uint64_t cap, n, nrels, sym;
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int elferr, i;
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if (gelf_getshdr(s->is, &ish) == NULL)
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errx(EXIT_FAILURE, "gelf_getehdr() failed: %s",
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elf_errmsg(-1));
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/* We don't want to touch relocation info for dynamic symbols. */
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if ((ecp->flags & SYMTAB_EXIST) == 0) {
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/*
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* No symbol table in output. If sh_link points to a section
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* that exists in the output object, this relocation section
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* is for dynamic symbols. Don't touch it.
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*/
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if (ish.sh_link != 0 && ecp->secndx[ish.sh_link] != 0)
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return;
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} else {
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/* Symbol table exist, check if index equals. */
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if (ish.sh_link != elf_ndxscn(ecp->symtab->is))
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return;
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}
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#define COPYREL(REL, SZ) do { \
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if (nrels == 0) { \
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if ((REL##SZ = malloc(cap * \
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sizeof(*REL##SZ))) == NULL) \
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err(EXIT_FAILURE, "malloc failed"); \
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} \
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if (nrels >= cap) { \
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cap *= 2; \
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if ((REL##SZ = realloc(REL##SZ, cap * \
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sizeof(*REL##SZ))) == NULL) \
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err(EXIT_FAILURE, "realloc failed"); \
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} \
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REL##SZ[nrels].r_offset = REL.r_offset; \
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REL##SZ[nrels].r_info = REL.r_info; \
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if (s->type == SHT_RELA) \
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rela##SZ[nrels].r_addend = rela.r_addend; \
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nrels++; \
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} while (0)
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nrels = 0;
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cap = 4; /* keep list is usually small. */
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rel32 = NULL;
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rel64 = NULL;
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rela32 = NULL;
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rela64 = NULL;
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if ((id = elf_getdata(s->is, NULL)) == NULL)
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errx(EXIT_FAILURE, "elf_getdata() failed: %s",
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elf_errmsg(-1));
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n = ish.sh_size / ish.sh_entsize;
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for(i = 0; (uint64_t)i < n; i++) {
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if (s->type == SHT_REL) {
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if (gelf_getrel(id, i, &rel) != &rel)
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errx(EXIT_FAILURE, "gelf_getrel failed: %s",
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elf_errmsg(-1));
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sym = GELF_R_SYM(rel.r_info);
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} else {
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if (gelf_getrela(id, i, &rela) != &rela)
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errx(EXIT_FAILURE, "gelf_getrel failed: %s",
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elf_errmsg(-1));
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sym = GELF_R_SYM(rela.r_info);
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}
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/*
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* If a relocation references a symbol and we are omitting
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* either that symbol or the entire symbol table we cannot
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* produce valid output, and so just omit the relocation.
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* Broken output like this is generally not useful, but some
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* uses of elfcopy/strip rely on it - for example, GCC's build
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* process uses it to check for build reproducibility by
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* stripping objects and comparing them.
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*
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* Relocations that do not reference a symbol are retained.
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*/
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if (sym != 0) {
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if (ish.sh_link == 0 || ecp->secndx[ish.sh_link] == 0)
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continue;
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name = elf_strptr(ecp->ein, elf_ndxscn(ecp->strtab->is),
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sym);
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if (name == NULL)
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errx(EXIT_FAILURE, "elf_strptr failed: %s",
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elf_errmsg(-1));
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if (lookup_symop_list(ecp, name, SYMOP_KEEP) == NULL)
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continue;
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}
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if (ecp->oec == ELFCLASS32) {
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if (s->type == SHT_REL)
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COPYREL(rel, 32);
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else
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COPYREL(rela, 32);
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} else {
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if (s->type == SHT_REL)
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COPYREL(rel, 64);
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else
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COPYREL(rela, 64);
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}
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}
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elferr = elf_errno();
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if (elferr != 0)
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errx(EXIT_FAILURE, "elf_getdata() failed: %s",
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elf_errmsg(elferr));
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if (ecp->oec == ELFCLASS32) {
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if (s->type == SHT_REL)
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s->buf = rel32;
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else
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s->buf = rela32;
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} else {
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if (s->type == SHT_REL)
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s->buf = rel64;
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else
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s->buf = rela64;
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}
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s->sz = gelf_fsize(ecp->eout, (s->type == SHT_REL ? ELF_T_REL :
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ELF_T_RELA), nrels, EV_CURRENT);
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s->nocopy = 1;
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}
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static void
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update_reloc(struct elfcopy *ecp, struct section *s)
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{
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