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Diffstat (limited to '')
| -rw-r--r-- | tools/objtool/special.c | 165 |
1 files changed, 165 insertions, 0 deletions
diff --git a/tools/objtool/special.c b/tools/objtool/special.c new file mode 100644 index 000000000..aff0cee7b --- /dev/null +++ b/tools/objtool/special.c @@ -0,0 +1,165 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Copyright (C) 2015 Josh Poimboeuf <jpoimboe@redhat.com> + */ + +/* + * 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 "builtin.h" +#include "special.h" +#include "warn.h" +#include "arch_special.h" + +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, + }, + {}, +}; + +void __weak arch_handle_alternative(unsigned short feature, struct special_alt *alt) +{ +} + +static void reloc_to_sec_off(struct reloc *reloc, struct section **sec, + unsigned long *off) +{ + *sec = reloc->sym->sec; + *off = reloc->sym->offset + reloc->addend; +} + +static int get_alt_entry(struct elf *elf, struct special_entry *entry, + struct section *sec, int idx, + struct special_alt *alt) +{ + struct reloc *orig_reloc, *new_reloc; + 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); + arch_handle_alternative(feature, alt); + } + + orig_reloc = find_reloc_by_dest(elf, sec, offset + entry->orig); + if (!orig_reloc) { + WARN_FUNC("can't find orig reloc", sec, offset + entry->orig); + return -1; + } + + reloc_to_sec_off(orig_reloc, &alt->orig_sec, &alt->orig_off); + + if (!entry->group || alt->new_len) { + new_reloc = find_reloc_by_dest(elf, sec, offset + entry->new); + if (!new_reloc) { + WARN_FUNC("can't find new reloc", + sec, offset + entry->new); + return -1; + } + + reloc_to_sec_off(new_reloc, &alt->new_sec, &alt->new_off); + + /* _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 > 0) + continue; + if (ret < 0) + return ret; + + list_add_tail(&alt->list, alts); + } + } + + return 0; +} |