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Diffstat (limited to 'tools/objtool/special.c')
| -rw-r--r-- | tools/objtool/special.c | 193 |
1 files changed, 193 insertions, 0 deletions
diff --git a/tools/objtool/special.c b/tools/objtool/special.c new file mode 100644 index 000000000..84f001d52 --- /dev/null +++ b/tools/objtool/special.c @@ -0,0 +1,193 @@ +/* + * Copyright (C) 2015 Josh Poimboeuf <jpoimboe@redhat.com> + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License + * as published by the Free Software Foundation; either version 2 + * of the License, or (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, see <http://www.gnu.org/licenses/>. + */ + +/* + * This file reads all the special sections which have alternate instructions + * which can be patched in or redirected to at runtime. + */ + +#include <stdlib.h> +#include <string.h> + +#include "special.h" +#include "warn.h" + +#define EX_ENTRY_SIZE 12 +#define EX_ORIG_OFFSET 0 +#define EX_NEW_OFFSET 4 + +#define JUMP_ENTRY_SIZE 24 +#define JUMP_ORIG_OFFSET 0 +#define JUMP_NEW_OFFSET 8 + +#define ALT_ENTRY_SIZE 13 +#define ALT_ORIG_OFFSET 0 +#define ALT_NEW_OFFSET 4 +#define ALT_FEATURE_OFFSET 8 +#define ALT_ORIG_LEN_OFFSET 10 +#define ALT_NEW_LEN_OFFSET 11 + +#define X86_FEATURE_POPCNT (4*32+23) + +struct special_entry { + const char *sec; + bool group, jump_or_nop; + unsigned char size, orig, new; + unsigned char orig_len, new_len; /* group only */ + unsigned char feature; /* ALTERNATIVE macro CPU feature */ +}; + +struct special_entry entries[] = { + { + .sec = ".altinstructions", + .group = true, + .size = ALT_ENTRY_SIZE, + .orig = ALT_ORIG_OFFSET, + .orig_len = ALT_ORIG_LEN_OFFSET, + .new = ALT_NEW_OFFSET, + .new_len = ALT_NEW_LEN_OFFSET, + .feature = ALT_FEATURE_OFFSET, + }, + { + .sec = "__jump_table", + .jump_or_nop = true, + .size = JUMP_ENTRY_SIZE, + .orig = JUMP_ORIG_OFFSET, + .new = JUMP_NEW_OFFSET, + }, + { + .sec = "__ex_table", + .size = EX_ENTRY_SIZE, + .orig = EX_ORIG_OFFSET, + .new = EX_NEW_OFFSET, + }, + {}, +}; + +static int get_alt_entry(struct elf *elf, struct special_entry *entry, + struct section *sec, int idx, + struct special_alt *alt) +{ + struct rela *orig_rela, *new_rela; + unsigned long offset; + + offset = idx * entry->size; + + alt->group = entry->group; + alt->jump_or_nop = entry->jump_or_nop; + + if (alt->group) { + alt->orig_len = *(unsigned char *)(sec->data->d_buf + offset + + entry->orig_len); + alt->new_len = *(unsigned char *)(sec->data->d_buf + offset + + entry->new_len); + } + + if (entry->feature) { + unsigned short feature; + + feature = *(unsigned short *)(sec->data->d_buf + offset + + entry->feature); + + /* + * It has been requested that we don't validate the !POPCNT + * feature path which is a "very very small percentage of + * machines". + */ + if (feature == X86_FEATURE_POPCNT) + alt->skip_orig = true; + } + + orig_rela = find_rela_by_dest(sec, offset + entry->orig); + if (!orig_rela) { + WARN_FUNC("can't find orig rela", sec, offset + entry->orig); + return -1; + } + if (orig_rela->sym->type != STT_SECTION) { + WARN_FUNC("don't know how to handle non-section rela symbol %s", + sec, offset + entry->orig, orig_rela->sym->name); + return -1; + } + + alt->orig_sec = orig_rela->sym->sec; + alt->orig_off = orig_rela->addend; + + if (!entry->group || alt->new_len) { + new_rela = find_rela_by_dest(sec, offset + entry->new); + if (!new_rela) { + WARN_FUNC("can't find new rela", + sec, offset + entry->new); + return -1; + } + + alt->new_sec = new_rela->sym->sec; + alt->new_off = (unsigned int)new_rela->addend; + + /* _ASM_EXTABLE_EX hack */ + if (alt->new_off >= 0x7ffffff0) + alt->new_off -= 0x7ffffff0; + } + + return 0; +} + +/* + * Read all the special sections and create a list of special_alt structs which + * describe all the alternate instructions which can be patched in or + * redirected to at runtime. + */ +int special_get_alts(struct elf *elf, struct list_head *alts) +{ + struct special_entry *entry; + struct section *sec; + unsigned int nr_entries; + struct special_alt *alt; + int idx, ret; + + INIT_LIST_HEAD(alts); + + for (entry = entries; entry->sec; entry++) { + sec = find_section_by_name(elf, entry->sec); + if (!sec) + continue; + + if (sec->len % entry->size != 0) { + WARN("%s size not a multiple of %d", + sec->name, entry->size); + return -1; + } + + nr_entries = sec->len / entry->size; + + for (idx = 0; idx < nr_entries; idx++) { + alt = malloc(sizeof(*alt)); + if (!alt) { + WARN("malloc failed"); + return -1; + } + memset(alt, 0, sizeof(*alt)); + + ret = get_alt_entry(elf, entry, sec, idx, alt); + if (ret) + return ret; + + list_add_tail(&alt->list, alts); + } + } + + return 0; +} |