From: Jack Brennen jbrennen@google.com

mainline inclusion from mainline-v6.7-rc1 commit 4074532758c5c367d3fcb8d124150824a254659d category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I97HOU CVE: NA

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Modify modpost to use binary search for converting addresses back into symbol references. Previously it used linear search.

This change saves a few seconds of wall time for defconfig builds, but can save several minutes on allyesconfigs.

Before: $ make LLVM=1 -j128 allyesconfig vmlinux -s KCFLAGS="-Wno-error" $ time scripts/mod/modpost -M -m -a -N -o vmlinux.symvers vmlinux.o 198.38user 1.27system 3:19.71elapsed

After: $ make LLVM=1 -j128 allyesconfig vmlinux -s KCFLAGS="-Wno-error" $ time scripts/mod/modpost -M -m -a -N -o vmlinux.symvers vmlinux.o 11.91user 0.85system 0:12.78elapsed

Signed-off-by: Jack Brennen jbrennen@google.com Tested-by: Nick Desaulniers ndesaulniers@google.com Signed-off-by: Masahiro Yamada masahiroy@kernel.org --- scripts/mod/Makefile | 4 +- scripts/mod/modpost.c | 70 ++------------ scripts/mod/modpost.h | 25 +++++ scripts/mod/symsearch.c | 199 ++++++++++++++++++++++++++++++++++++++++ 4 files changed, 232 insertions(+), 66 deletions(-) create mode 100644 scripts/mod/symsearch.c

diff --git a/scripts/mod/Makefile b/scripts/mod/Makefile index c9e38ad937fd..3c54125eb373 100644 --- a/scripts/mod/Makefile +++ b/scripts/mod/Makefile @@ -5,7 +5,7 @@ CFLAGS_REMOVE_empty.o += $(CC_FLAGS_LTO) hostprogs-always-y += modpost mk_elfconfig always-y += empty.o

-modpost-objs := modpost.o file2alias.o sumversion.o +modpost-objs := modpost.o file2alias.o sumversion.o symsearch.o

devicetable-offsets-file := devicetable-offsets.h

@@ -16,7 +16,7 @@ targets += $(devicetable-offsets-file) devicetable-offsets.s

# dependencies on generated files need to be listed explicitly

-$(obj)/modpost.o $(obj)/file2alias.o $(obj)/sumversion.o: $(obj)/elfconfig.h +$(obj)/modpost.o $(obj)/file2alias.o $(obj)/sumversion.o $(obj)/symsearch.o: $(obj)/elfconfig.h $(obj)/file2alias.o: $(obj)/$(devicetable-offsets-file)

quiet_cmd_elfconfig = MKELF $@ diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c index ac4ef3e206bb..e6c8b096362e 100644 --- a/scripts/mod/modpost.c +++ b/scripts/mod/modpost.c @@ -22,7 +22,6 @@ #include <errno.h> #include "modpost.h" #include "../../include/linux/license.h" -#include "../../include/linux/module_symbol.h"

static bool module_enabled; /* Are we using CONFIG_MODVERSIONS? */ @@ -577,11 +576,14 @@ static int parse_elf(struct elf_info *info, const char *filename) *p = TO_NATIVE(*p); }

+ symsearch_init(info); + return 1; }

static void parse_elf_finish(struct elf_info *info) { + symsearch_finish(info); release_file(info->hdr, info->size); }

@@ -1050,71 +1052,10 @@ static int secref_whitelist(const char *fromsec, const char *fromsym, return 1; }

-/* - * If there's no name there, ignore it; likewise, ignore it if it's - * one of the magic symbols emitted used by current tools. - * - * Otherwise if find_symbols_between() returns those symbols, they'll - * fail the whitelist tests and cause lots of false alarms ... fixable - * only by merging __exit and __init sections into __text, bloating - * the kernel (which is especially evil on embedded platforms). - */ -static inline int is_valid_name(struct elf_info *elf, Elf_Sym *sym) -{ - const char *name = elf->strtab + sym->st_name; - - if (!name || !strlen(name)) - return 0; - return !is_mapping_symbol(name); -} - -/* Look up the nearest symbol based on the section and the address */ -static Elf_Sym *find_nearest_sym(struct elf_info *elf, Elf_Addr addr, - unsigned int secndx, bool allow_negative, - Elf_Addr min_distance) -{ - Elf_Sym *sym; - Elf_Sym *near = NULL; - Elf_Addr sym_addr, distance; - bool is_arm = (elf->hdr->e_machine == EM_ARM); - - for (sym = elf->symtab_start; sym < elf->symtab_stop; sym++) { - if (get_secindex(elf, sym) != secndx) - continue; - if (!is_valid_name(elf, sym)) - continue; - - sym_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) - sym_addr &= ~1; - - if (addr >= sym_addr) - distance = addr - sym_addr; - else if (allow_negative) - distance = sym_addr - addr; - else - continue; - - if (distance <= min_distance) { - min_distance = distance; - near = sym; - } - - if (min_distance == 0) - break; - } - return near; -} - static Elf_Sym *find_fromsym(struct elf_info *elf, Elf_Addr addr, unsigned int secndx) { - return find_nearest_sym(elf, addr, secndx, false, ~0); + return symsearch_find_nearest(elf, addr, secndx, false, ~0); }

static Elf_Sym *find_tosym(struct elf_info *elf, Elf_Addr addr, Elf_Sym *sym) @@ -1127,7 +1068,8 @@ static Elf_Sym *find_tosym(struct elf_info *elf, Elf_Addr addr, Elf_Sym *sym) * Strive to find a better symbol name, but the resulting name may not * match the symbol referenced in the original code. */ - return find_nearest_sym(elf, addr, get_secindex(elf, sym), true, 20); + return symsearch_find_nearest(elf, addr, get_secindex(elf, sym), + true, 20); }

static bool is_executable_section(struct elf_info *elf, unsigned int secndx) diff --git a/scripts/mod/modpost.h b/scripts/mod/modpost.h index 5f94c2c9f2d9..6413f26fcb6b 100644 --- a/scripts/mod/modpost.h +++ b/scripts/mod/modpost.h @@ -10,6 +10,7 @@ #include <fcntl.h> #include <unistd.h> #include <elf.h> +#include "../../include/linux/module_symbol.h"

#include "list.h" #include "elfconfig.h" @@ -128,6 +129,8 @@ struct elf_info { * take shndx from symtab_shndx_start[N] instead */ Elf32_Word *symtab_shndx_start; Elf32_Word *symtab_shndx_stop; + + struct symsearch *symsearch; };

/* Accessor for sym->st_shndx, hides ugliness of "64k sections" */ @@ -154,6 +157,28 @@ static inline unsigned int get_secindex(const struct elf_info *info, return index; }

+/* + * If there's no name there, ignore it; likewise, ignore it if it's + * one of the magic symbols emitted used by current tools. + * + * Internal symbols created by tools should be ignored by modpost. + */ +static inline int is_valid_name(struct elf_info *elf, Elf_Sym *sym) +{ + const char *name = elf->strtab + sym->st_name; + + if (!name || !strlen(name)) + return 0; + return !is_mapping_symbol(name); +} + +/* symsearch.c */ +void symsearch_init(struct elf_info *elf); +void symsearch_finish(struct elf_info *elf); +Elf_Sym *symsearch_find_nearest(struct elf_info *elf, Elf_Addr addr, + unsigned int secndx, bool allow_negative, + Elf_Addr min_distance); + /* file2alias.c */ void handle_moddevtable(struct module *mod, struct elf_info *info, Elf_Sym *sym, const char *symname); diff --git a/scripts/mod/symsearch.c b/scripts/mod/symsearch.c new file mode 100644 index 000000000000..aa4ed51f9960 --- /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; +}