diff options
Diffstat (limited to 'scripts/mod/symsearch.c')
| -rw-r--r-- | scripts/mod/symsearch.c | 199 |
1 files changed, 199 insertions, 0 deletions
diff --git a/scripts/mod/symsearch.c b/scripts/mod/symsearch.c new file mode 100644 index 0000000000..aa4ed51f99 --- /dev/null +++ b/scripts/mod/symsearch.c @@ -0,0 +1,199 @@ +// SPDX-License-Identifier: GPL-2.0 + +/* + * Helper functions for finding the symbol in an ELF which is "nearest" + * to a given address. + */ + +#include "modpost.h" + +struct syminfo { + unsigned int symbol_index; + unsigned int section_index; + Elf_Addr addr; +}; + +/* + * Container used to hold an entire binary search table. + * Entries in table are ascending, sorted first by section_index, + * then by addr, and last by symbol_index. The sorting by + * symbol_index is used to ensure predictable behavior when + * multiple symbols are present with the same address; all + * symbols past the first are effectively ignored, by eliding + * them in symsearch_fixup(). + */ +struct symsearch { + unsigned int table_size; + struct syminfo table[]; +}; + +static int syminfo_compare(const void *s1, const void *s2) +{ + const struct syminfo *sym1 = s1; + const struct syminfo *sym2 = s2; + + if (sym1->section_index > sym2->section_index) + return 1; + if (sym1->section_index < sym2->section_index) + return -1; + if (sym1->addr > sym2->addr) + return 1; + if (sym1->addr < sym2->addr) + return -1; + if (sym1->symbol_index > sym2->symbol_index) + return 1; + if (sym1->symbol_index < sym2->symbol_index) + return -1; + return 0; +} + +static unsigned int symbol_count(struct elf_info *elf) +{ + unsigned int result = 0; + + for (Elf_Sym *sym = elf->symtab_start; sym < elf->symtab_stop; sym++) { + if (is_valid_name(elf, sym)) + result++; + } + return result; +} + +/* + * Populate the search array that we just allocated. + * Be slightly paranoid here. The ELF file is mmap'd and could + * conceivably change between symbol_count() and symsearch_populate(). + * If we notice any difference, bail out rather than potentially + * propagating errors or crashing. + */ +static void symsearch_populate(struct elf_info *elf, + struct syminfo *table, + unsigned int table_size) +{ + bool is_arm = (elf->hdr->e_machine == EM_ARM); + + for (Elf_Sym *sym = elf->symtab_start; sym < elf->symtab_stop; sym++) { + if (is_valid_name(elf, sym)) { + if (table_size-- == 0) + fatal("%s: size mismatch\n", __func__); + table->symbol_index = sym - elf->symtab_start; + table->section_index = get_secindex(elf, sym); + table->addr = sym->st_value; + + /* + * For ARM Thumb instruction, the bit 0 of st_value is + * set if the symbol is STT_FUNC type. Mask it to get + * the address. + */ + if (is_arm && ELF_ST_TYPE(sym->st_info) == STT_FUNC) + table->addr &= ~1; + + table++; + } + } + + if (table_size != 0) + fatal("%s: size mismatch\n", __func__); +} + +/* + * Do any fixups on the table after sorting. + * For now, this just finds adjacent entries which have + * the same section_index and addr, and it propagates + * the first symbol_index over the subsequent entries, + * so that only one symbol_index is seen for any given + * section_index and addr. This ensures that whether + * we're looking at an address from "above" or "below" + * that we see the same symbol_index. + * This does leave some duplicate entries in the table; + * in practice, these are a small fraction of the + * total number of entries, and they are harmless to + * the binary search algorithm other than a few occasional + * unnecessary comparisons. + */ +static void symsearch_fixup(struct syminfo *table, unsigned int table_size) +{ + /* Don't look at index 0, it will never change. */ + for (unsigned int i = 1; i < table_size; i++) { + if (table[i].addr == table[i - 1].addr && + table[i].section_index == table[i - 1].section_index) { + table[i].symbol_index = table[i - 1].symbol_index; + } + } +} + +void symsearch_init(struct elf_info *elf) +{ + unsigned int table_size = symbol_count(elf); + + elf->symsearch = NOFAIL(malloc(sizeof(struct symsearch) + + sizeof(struct syminfo) * table_size)); + elf->symsearch->table_size = table_size; + + symsearch_populate(elf, elf->symsearch->table, table_size); + qsort(elf->symsearch->table, table_size, + sizeof(struct syminfo), syminfo_compare); + + symsearch_fixup(elf->symsearch->table, table_size); +} + +void symsearch_finish(struct elf_info *elf) +{ + free(elf->symsearch); + elf->symsearch = NULL; +} + +/* + * Find the syminfo which is in secndx and "nearest" to addr. + * allow_negative: allow returning a symbol whose address is > addr. + * min_distance: ignore symbols which are further away than this. + * + * Returns a pointer into the symbol table for success. + * Returns NULL if no legal symbol is found within the requested range. + */ +Elf_Sym *symsearch_find_nearest(struct elf_info *elf, Elf_Addr addr, + unsigned int secndx, bool allow_negative, + Elf_Addr min_distance) +{ + unsigned int hi = elf->symsearch->table_size; + unsigned int lo = 0; + struct syminfo *table = elf->symsearch->table; + struct syminfo target; + + target.addr = addr; + target.section_index = secndx; + target.symbol_index = ~0; /* compares greater than any actual index */ + while (hi > lo) { + unsigned int mid = lo + (hi - lo) / 2; /* Avoids overflow */ + + if (syminfo_compare(&table[mid], &target) > 0) + hi = mid; + else + lo = mid + 1; + } + + /* + * table[hi], if it exists, is the first entry in the array which + * lies beyond target. table[hi - 1], if it exists, is the last + * entry in the array which comes before target, including the + * case where it perfectly matches the section and the address. + * + * Note -- if the address we're looking up falls perfectly + * in the middle of two symbols, this is written to always + * prefer the symbol with the lower address. + */ + Elf_Sym *result = NULL; + + if (allow_negative && + hi < elf->symsearch->table_size && + table[hi].section_index == secndx && + table[hi].addr - addr <= min_distance) { + min_distance = table[hi].addr - addr; + result = &elf->symtab_start[table[hi].symbol_index]; + } + if (hi > 0 && + table[hi - 1].section_index == secndx && + addr - table[hi - 1].addr <= min_distance) { + result = &elf->symtab_start[table[hi - 1].symbol_index]; + } + return result; +} |