objtool: Check for gelf_update_rel[a] failures

Otherwise, if these fail we end up with garbage data in the
.rela.orc_unwind_ip section, leading to errors like

  ld: fs/squashfs/namei.o: bad reloc symbol index (0x7f16 >= 0x12) for offset 0x7f16d5c82cc8 in section `.orc_unwind_ip'
Signed-off-by: Michael Forney <mforney@mforney.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20210509000103.11008-1-mforney@mforney.org

tools/objtool/elf.c

@@ -1001,7 +1001,10 @@ static int elf_rebuild_rel_reloc_section(struct section *sec, int nr)
 	list_for_each_entry(reloc, &sec->reloc_list, list) {
 		reloc->rel.r_offset = reloc->offset;
 		reloc->rel.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
-		gelf_update_rel(sec->data, idx, &reloc->rel);
+		if (!gelf_update_rel(sec->data, idx, &reloc->rel)) {
+			WARN_ELF("gelf_update_rel");
+			return -1;
+		}
 		idx++;
 	}
 
@@ -1033,7 +1036,10 @@ static int elf_rebuild_rela_reloc_section(struct section *sec, int nr)
 		reloc->rela.r_offset = reloc->offset;
 		reloc->rela.r_addend = reloc->addend;
 		reloc->rela.r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
-		gelf_update_rela(sec->data, idx, &reloc->rela);
+		if (!gelf_update_rela(sec->data, idx, &reloc->rela)) {
+			WARN_ELF("gelf_update_rela");
+			return -1;
+		}
 		idx++;
 	}