On Fri, 14 Jul 2023 15:03:26 +0000 Alessandro Carminati <alessandro.carminati@xxxxxxxxx> wrote: > It is not uncommon for drivers or modules related to similar peripherals > to have symbols with the exact same name. > While this is not a problem for the kernel's binary itself, it becomes an > issue when attempting to trace or probe specific functions using > infrastructure like ftrace or kprobe. > > The tracing subsystem relies on the `nm -n vmlinux` output, which provides > symbol information from the kernel's ELF binary. However, when multiple > symbols share the same name, the standard nm output does not differentiate > between them. This can lead to confusion and difficulty when trying to > probe the intended symbol. > > ~ # cat /proc/kallsyms | grep " name_show" > ffffffff8c4f76d0 t name_show > ffffffff8c9cccb0 t name_show > ffffffff8cb0ac20 t name_show > ffffffff8cc728c0 t name_show > ffffffff8ce0efd0 t name_show > ffffffff8ce126c0 t name_show > ffffffff8ce1dd20 t name_show > ffffffff8ce24e70 t name_show > ffffffff8d1104c0 t name_show > ffffffff8d1fe480 t name_show > > **kas_alias** addresses this challenge by extending the symbol names with > unique suffixes during the kernel build process. > The newly created aliases for these duplicated symbols are unique names > that can be fed to the ftracefs interface. By doing so, it enables > previously unreachable symbols to be probed. > > ~ # cat /proc/kallsyms | grep " name_show" > ffffffff974f76d0 t name_show > ffffffff974f76d0 t name_show__alias__6340 > ffffffff979cccb0 t name_show > ffffffff979cccb0 t name_show__alias__6341 > ffffffff97b0ac20 t name_show > ffffffff97b0ac20 t name_show__alias__6342 > ffffffff97c728c0 t name_show > ffffffff97c728c0 t name_show__alias__6343 > ffffffff97e0efd0 t name_show > ffffffff97e0efd0 t name_show__alias__6344 > ffffffff97e126c0 t name_show > ffffffff97e126c0 t name_show__alias__6345 > ffffffff97e1dd20 t name_show > ffffffff97e1dd20 t name_show__alias__6346 > ffffffff97e24e70 t name_show > ffffffff97e24e70 t name_show__alias__6347 > ffffffff981104c0 t name_show > ffffffff981104c0 t name_show__alias__6348 > ffffffff981fe480 t name_show > ffffffff981fe480 t name_show__alias__6349 > ~ # echo "p:kprobes/evnt1 name_show__alias__6349" \ > > >/sys/kernel/tracing/kprobe_events > ~ # cat /sys/kernel/tracing/kprobe_events > p:kprobes/evnt1 name_show__alias__6349 > Honestly, I think the "_alias_<some-random-number>" is useless. It doesn't give you any clue to what function you are actually attaching to. There's been other approaches that show module and/or file names. I know there's still some issues with getting those accepted, but I much rather have them than this! See: https://lore.kernel.org/all/20221205163157.269335-1-nick.alcock@xxxxxxxxxx/ -- Steve > Changes from v1: > - Integrated changes requested by Masami to exclude symbols with prefixes > "_cfi" and "_pfx". > - Introduced a small framework to handle patterns that need to be excluded > from the alias production. > - Excluded other symbols using the framework. > - Introduced the ability to discriminate between text and data symbols. > - Added two new config symbols in this version: CONFIG_KALLSYMS_ALIAS_DATA, > which allows data for data, and CONFIG_KALLSYMS_ALIAS_DATA_ALL, which > excludes all filters and provides an alias for each duplicated symbol. > > https://lore.kernel.org/all/20230711151925.1092080-1-alessandro.carminati@xxxxxxxxx/ > > Signed-off-by: Alessandro Carminati (Red Hat) <alessandro.carminati@xxxxxxxxx> > --- > init/Kconfig | 36 +++++ > scripts/Makefile | 4 + > scripts/kas_alias/Makefile | 4 + > scripts/kas_alias/duplicates_list.c | 70 +++++++++ > scripts/kas_alias/duplicates_list.h | 15 ++ > scripts/kas_alias/item_list.c | 230 ++++++++++++++++++++++++++++ > scripts/kas_alias/item_list.h | 26 ++++ > scripts/kas_alias/kas_alias.c | 186 ++++++++++++++++++++++ > scripts/link-vmlinux.sh | 6 +- > 9 files changed, 576 insertions(+), 1 deletion(-) > create mode 100644 scripts/kas_alias/Makefile > create mode 100644 scripts/kas_alias/duplicates_list.c > create mode 100644 scripts/kas_alias/duplicates_list.h > create mode 100644 scripts/kas_alias/item_list.c > create mode 100644 scripts/kas_alias/item_list.h > create mode 100644 scripts/kas_alias/kas_alias.c > > diff --git a/init/Kconfig b/init/Kconfig > index f7f65af4ee12..5ae7c613cdc4 100644 > --- a/init/Kconfig > +++ b/init/Kconfig > @@ -1737,6 +1737,42 @@ config KALLSYMS_BASE_RELATIVE > time constants, and no relocation pass is required at runtime to fix > up the entries based on the runtime load address of the kernel. > > +config KALLSYMS_ALIAS > + bool "Produces alias for duplicated symbols" if EXPERT > + depends on KALLSYMS > + help > + It is not uncommon for drivers or modules related to similar > + peripherals to have symbols with the exact same name. > + While this is not a problem for the kernel's binary itself, it > + becomes an issue when attempting to trace or probe specific > + functions using infrastructure like ftrace or kprobe. > + > + This option addresses this challenge by extending the symbol names > + with unique suffixes during the kernel build process. > + The newly created aliases for these duplicated symbols are unique > + names that can be fed to the ftrace sysfs interface. By doing so, it > + enables previously unreachable symbols to be probed. > + > +config CONFIG_KALLSYMS_ALIAS_DATA > + bool "Produces alias also for data" > + depends on KALLSYMS_ALIAS > + help > + Sometimes it can be useful to refer to data. In live patch scenarios, > + you may find yourself needing to use symbols that are shared with > + other functions. Since symbols face the same issue as functions, this > + option allows you to create aliases for data as well. > + > +config CONFIG_KALLSYMS_ALIAS_DATA_ALL > + bool "Removes all filter when producing data alias" > + depends on CONFIG_KALLSYMS_ALIAS_DATA > + help > + When selecting data aliases, not all symbols are included in the set > + This is because many symbols are unlikely to be used. If you choose > + to have an alias for all data symbols, be aware that it will > + significantly increase the size. > + > + If unsure, say N. > + > # end of the "standard kernel features (expert users)" menu > > # syscall, maps, verifier > diff --git a/scripts/Makefile b/scripts/Makefile > index 32b6ba722728..65fafe17cfe5 100644 > --- a/scripts/Makefile > +++ b/scripts/Makefile > @@ -49,3 +49,7 @@ subdir-$(CONFIG_SECURITY_SELINUX) += selinux > > # Let clean descend into subdirs > subdir- += basic dtc gdb kconfig mod > + > +# KALLSyms alias > +subdir-$(CONFIG_KALLSYMS_ALIAS) += kas_alias > + > diff --git a/scripts/kas_alias/Makefile b/scripts/kas_alias/Makefile > new file mode 100644 > index 000000000000..523fa3441013 > --- /dev/null > +++ b/scripts/kas_alias/Makefile > @@ -0,0 +1,4 @@ > +# SPDX-License-Identifier: GPL-2.0 > +hostprogs-always-$(CONFIG_KALLSYMS_ALIAS) += kas_alias > + > +kas_alias-objs := duplicates_list.o item_list.o kas_alias.o > diff --git a/scripts/kas_alias/duplicates_list.c b/scripts/kas_alias/duplicates_list.c > new file mode 100644 > index 000000000000..e7a3d2917937 > --- /dev/null > +++ b/scripts/kas_alias/duplicates_list.c > @@ -0,0 +1,70 @@ > +// SPDX-License-Identifier: GPL-2.0-or-later > +#include <stdint.h> > +#include <stdio.h> > +#include <string.h> > +#include <stdlib.h> > +#include <stdbool.h> > + > +#include "item_list.h" > +#include "duplicates_list.h" > + > +struct duplicate_item *find_duplicates(struct item *list) > +{ > + struct duplicate_item *current_duplicate = NULL; > + struct duplicate_item *duplicates = NULL; > + struct duplicate_item *new_duplicate; > + struct item *current_item = list; > + bool prev_was_duplicate = false; > + struct item *prev_item = NULL; > + > + while (current_item) { > + if ((prev_item && (strcmp(current_item->symb_name, prev_item->symb_name) == 0)) || > + prev_was_duplicate) { > + if (!duplicates) { > + duplicates = malloc(sizeof(struct duplicate_item)); > + if (!duplicates) > + return NULL; > + > + duplicates->original_item = prev_item; > + duplicates->next = NULL; > + current_duplicate = duplicates; > + } else { > + new_duplicate = malloc(sizeof(struct duplicate_item)); > + if (!new_duplicate) { > + free_duplicates(&duplicates); > + return NULL; > + } > + > + new_duplicate->original_item = prev_item; > + new_duplicate->next = NULL; > + current_duplicate->next = new_duplicate; > + current_duplicate = new_duplicate; > + > + if ((strcmp(current_item->symb_name, prev_item->symb_name) != 0) && > + (prev_was_duplicate)) > + prev_was_duplicate = false; > + else > + prev_was_duplicate = true; > + } > + } > + > + prev_item = current_item; > + current_item = current_item->next; > + } > + > + return duplicates; > +} > + > +void free_duplicates(struct duplicate_item **duplicates) > +{ > + struct duplicate_item *duplicates_iterator = *duplicates; > + struct duplicate_item *app; > + > + while (duplicates_iterator) { > + app = duplicates_iterator; > + duplicates_iterator = duplicates_iterator->next; > + free(app); > + } > + > + *duplicates = NULL; > +} > diff --git a/scripts/kas_alias/duplicates_list.h b/scripts/kas_alias/duplicates_list.h > new file mode 100644 > index 000000000000..76aa73e584bc > --- /dev/null > +++ b/scripts/kas_alias/duplicates_list.h > @@ -0,0 +1,15 @@ > +/* SPDX-License-Identifier: GPL-2.0-or-later */ > +#ifndef DUPLICATES_LIST_H > +#define DUPLICATES_LIST_H > + > +#include "item_list.h" > + > +struct duplicate_item { > + struct item *original_item; > + struct duplicate_item *next; > +}; > + > +struct duplicate_item *find_duplicates(struct item *list); > +void free_duplicates(struct duplicate_item **duplicates); > + > +#endif > diff --git a/scripts/kas_alias/item_list.c b/scripts/kas_alias/item_list.c > new file mode 100644 > index 000000000000..7c9d5aecca9a > --- /dev/null > +++ b/scripts/kas_alias/item_list.c > @@ -0,0 +1,230 @@ > +// SPDX-License-Identifier: GPL-2.0-or-later > +#include <stdio.h> > +#include <stdlib.h> > +#include <stdint.h> > +#include <string.h> > +#include <stdbool.h> > +#include <assert.h> > +#include "item_list.h" > + > +#define CHECK_ORDER_BY_ADDRESS(sort_by, current, temp, op) \ > + ((sort_by) == BY_ADDRESS && (current)->addr op (temp)->addr) > +#define CHECK_ORDER_BY_NAME(sort_by, current, temp, op) \ > + ((sort_by) == BY_NAME && strcmp((current)->symb_name, (temp)->symb_name) op 0) > + > +struct item *list_index[96] = {0}; > + > +void build_index(struct item *list) > +{ > + char current_first_letter = ' '; > + struct item *current = list; > + > + while (current) { > + if (current->symb_name[0] != current_first_letter) { > + current_first_letter = current->symb_name[0]; > + list_index[current_first_letter - 32] = current; > + } > + current = current->next; > + } > +} > + > +struct item *add_item(struct item **list, const char *name, char stype, uint64_t addr) > +{ > + struct item *new_item; > + struct item *current; > + > + new_item = malloc(sizeof(struct item)); > + if (!new_item) > + return NULL; > + > + strncpy(new_item->symb_name, name, MAX_NAME_SIZE); > + new_item->symb_name[MAX_NAME_SIZE - 1] = '\0'; > + new_item->addr = addr; > + new_item->stype = stype; > + new_item->next = NULL; > + > + if (!(*list)) { > + *list = new_item; > + } else { > + current = *list; > + while (current->next) > + current = current->next; > + > + current->next = new_item; > + } > + return new_item; > +} > + > +void sort_list(struct item **list, int sort_by) > +{ > + struct item *current = *list; > + struct item *sorted = NULL; > + struct item *next_item; > + struct item *temp; > + > + if (!(*list) || !((*list)->next)) > + return; > + > + while (current) { > + next_item = current->next; > + if (!sorted || > + (CHECK_ORDER_BY_ADDRESS(sort_by, current, sorted, <) || > + CHECK_ORDER_BY_NAME(sort_by, current, sorted, >=))) { > + current->next = sorted; > + sorted = current; > + } else { > + temp = sorted; > + while (temp->next && > + (CHECK_ORDER_BY_ADDRESS(sort_by, current, temp->next, >=) || > + CHECK_ORDER_BY_NAME(sort_by, current, temp->next, >=))) > + temp = temp->next; > + > + current->next = temp->next; > + temp->next = current; > + } > + current = next_item; > + } > + > + *list = sorted; > +} > + > +struct item *merge(struct item *left, struct item *right, int sort_by) > +{ > + struct item *current = NULL; > + struct item *result = NULL; > + > + if (!left) > + return right; > + if (!right) > + return left; > + > + if (sort_by == BY_NAME) { > + if (strcmp(left->symb_name, right->symb_name) <= 0) { > + result = left; > + left = left->next; > + } else { > + result = right; > + right = right->next; > + } > + } else { > + if (sort_by == BY_ADDRESS) { > + if (left->addr <= right->addr) { > + result = left; > + left = left->next; > + } else { > + result = right; > + right = right->next; > + } > + } > + } > + > + current = result; > + > + while (left && right) { > + if (sort_by == BY_NAME) { > + if (strcmp(left->symb_name, right->symb_name) <= 0) { > + current->next = left; > + left = left->next; > + } else { > + current->next = right; > + right = right->next; > + } > + } else { > + if (sort_by == BY_ADDRESS) { > + if (left->addr <= right->addr) { > + current->next = left; > + left = left->next; > + } else { > + current->next = right; > + right = right->next; > + } > + } > + } > + > + current = current->next; > + } > + > + if (left) { > + current->next = left; > + } else { > + if (right) > + current->next = right; > + } > + > + return result; > +} > + > +struct item *merge_sort(struct item *head, int sort_by) > +{ > + struct item *right; > + struct item *slow; > + struct item *fast; > + struct item *left; > + > + if (!head || !head->next) > + return head; > + > + slow = head; > + fast = head->next; > + > + while (fast && fast->next) { > + slow = slow->next; > + fast = fast->next->next; > + } > + > + left = head; > + right = slow->next; > + slow->next = NULL; > + > + left = merge_sort(left, sort_by); > + right = merge_sort(right, sort_by); > + > + return merge(left, right, sort_by); > +} > + > +void sort_list_m(struct item **head, int sort_by) > +{ > + if (!(*head) || !((*head)->next)) > + return; > + > + *head = merge_sort(*head, sort_by); > +} > + > +int insert_after(struct item *list, const uint64_t search_addr, > + const char *name, uint64_t addr, char stype) > +{ > + struct item *new_item; > + struct item *current; > + int ret = 0; > + > + current = (list_index[name[0] - 32]) ? list_index[name[0] - 32] : list; > + while (current) { > + if (current->addr == search_addr) { > + new_item = malloc(sizeof(struct item)); > + if (!new_item) > + return ret; > + strncpy(new_item->symb_name, name, MAX_NAME_SIZE); > + new_item->symb_name[MAX_NAME_SIZE - 1] = '\0'; > + new_item->addr = addr; > + new_item->stype = stype; > + new_item->next = current->next; > + current->next = new_item; > + ret = 1; > + break; > + } > + current = current->next; > + } > + return ret; > +} > + > +void free_items(struct item **head) > +{ > + struct item *app, *item_iterator = *head; > + > + while (item_iterator) { > + app = item_iterator; > + item_iterator = item_iterator->next; > + free(app); > + } > + *head = NULL; > +} > diff --git a/scripts/kas_alias/item_list.h b/scripts/kas_alias/item_list.h > new file mode 100644 > index 000000000000..b4891cb088ee > --- /dev/null > +++ b/scripts/kas_alias/item_list.h > @@ -0,0 +1,26 @@ > +/* SPDX-License-Identifier: GPL-2.0-or-later */ > +#ifndef ITEM_LIST_H > +#define ITEM_LIST_H > +#include <stdint.h> > + > +#define MAX_NAME_SIZE 256 > +#define BY_ADDRESS 1 > +#define BY_NAME 2 > + > +struct item { > + char symb_name[MAX_NAME_SIZE]; > + uint64_t addr; > + char stype; > + struct item *next; > +}; > + > +void build_index(struct item *list); > +struct item *add_item(struct item **list, const char *name, char stype, uint64_t addr); > +void sort_list(struct item **list, int sort_by); > +struct item *merge(struct item *left, struct item *right, int sort_by); > +struct item *merge_sort(struct item *head, int sort_by); > +void sort_list_m(struct item **head, int sort_by); > +int insert_after(struct item *list, const uint64_t search_addr, > + const char *name, uint64_t addr, char stype); > +void free_items(struct item **head); > +#endif > diff --git a/scripts/kas_alias/kas_alias.c b/scripts/kas_alias/kas_alias.c > new file mode 100644 > index 000000000000..eb873b368023 > --- /dev/null > +++ b/scripts/kas_alias/kas_alias.c > @@ -0,0 +1,186 @@ > +// SPDX-License-Identifier: GPL-2.0-or-later > +#include <stdio.h> > +#include <stdlib.h> > +#include <stdint.h> > +#include <string.h> > +#include <stdbool.h> > +#include <stdarg.h> > +#include <regex.h> > + > +#include "item_list.h" > +#include "duplicates_list.h" > + > +#define SYMB_IS_TEXT(s) ((((s)->stype) == 't') || (((s)->stype) == 'T')) > +#define SYMB_IS_DATA(s) ((((s)->stype) == 'b') || (((s)->stype) == 'B') || \ > + (((s)->stype) == 'd') || (((s)->stype) == 'D') || \ > + (((s)->stype) == 'r') || (((s)->stype) == 'R')) > +#ifdef CONFIG_KALLSYMS_ALIAS_DATA > +#define SYMB_NEEDS_ALIAS(s) (SYMB_IS_TEXT(s) || SYMB_IS_DATA(s)) > +#else > +#define SYMB_NEEDS_ALIAS(s) SYMB_IS_TEXT(s) > +#endif > +#define FNOMATCH 0 > +#define FMATCH 1 > +#define EREGEX 2 > + > +const char *ignore_regex[] = { > + "^__cfi_.*$", // __cfi_ preamble > +#ifndef CONFIG_KALLSYMS_ALIAS_DATA_ALL > + "^_*TRACE_SYSTEM.*$", > + "^__already_done\\.[0-9]+$", // Call a function once data > + "^___tp_str\\.[0-9]+$", > + "^___done\\.[0-9]+$", > + "^__print_once\\.[0-9]+$", > + "^_rs\\.[0-9]+$", > + "^__compound_literal\\.[0-9]+$", > + "^___once_key\\.[0-9]+$", > + "^__func__\\.[0-9]+$", > + "^__msg\\.[0-9]+$", > + "^CSWTCH\\.[0-9]+$", > + "^__flags\\.[0-9]+$", > + "^__wkey.*$", > + "^__mkey.*$", > + "^__key.*$", > +#endif > + "^__pfx_.*$" // NOP-padding > +}; > + > +int suffix_serial; > + > +static inline void verbose_msg(bool verbose, const char *fmt, ...) > +{ > + va_list args; > + > + va_start(args, fmt); > + if (verbose) > + printf(fmt, args); > + > + va_end(args); > +} > + > +static void create_suffix(const char *name, char *output_suffix) > +{ > + sprintf(output_suffix, "%s__alias__%d", name, suffix_serial++); > +} > + > +static int filter_symbols(char *symbol, const char **ignore_list, int regex_no) > +{ > + regex_t regex; > + int res, i; > + > + for (i = 0; i < regex_no; i++) { > + res = regcomp(®ex, ignore_list[i], REG_EXTENDED); > + if (res) > + return -EREGEX; > + > + res = regexec(®ex, symbol, 0, NULL, 0); > + regfree(®ex); > + switch (res) { > + case 0: > + return FMATCH; > + case REG_NOMATCH: > + break; > + default: > + return -EREGEX; > + } > + > + } > + > + return FNOMATCH; > +} > + > +int main(int argc, char *argv[]) > +{ > + char t, sym_name[MAX_NAME_SIZE], new_name[MAX_NAME_SIZE + 15]; > + struct duplicate_item *duplicate_iterator; > + struct duplicate_item *duplicate; > + struct item *head = {NULL}; > + bool need_2_process = true; > + struct item *last = {NULL}; > + struct item *current; > + int verbose_mode = 0; > + uint64_t address; > + FILE *fp; > + int res; > + > + if (argc < 2 || argc > 3) { > + printf("Usage: %s <nmfile> [-verbose]\n", argv[0]); > + return 1; > + } > + > + if (argc == 3 && strcmp(argv[2], "-verbose") == 0) > + verbose_mode = 1; > + > + verbose_msg(verbose_mode, "Scanning nm data(%s)\n", argv[1]); > + > + fp = fopen(argv[1], "r"); > + if (!fp) { > + printf("Can't open input file.\n"); > + return 1; > + } > + > + while (fscanf(fp, "%lx %c %99s\n", &address, &t, sym_name) == 3) { > + if (strstr(sym_name, "__alias__1") != NULL) { > + if (verbose_mode && need_2_process) > + printf("Already processed\n"); > + need_2_process = false; > + } > + last = add_item(&last, sym_name, t, address); > + if (!last) { > + printf("Error in allocate memory\n"); > + free_items(&head); > + return 1; > + } > + > + if (!head) > + head = last; > + } > + > + fclose(fp); > + > + if (need_2_process) { > + verbose_msg(verbose_mode, "Sorting nm data\n"); > + sort_list_m(&head, BY_NAME); > + verbose_msg(verbose_mode, "Scanning nm data for duplicates\n"); > + duplicate = find_duplicates(head); > + if (!duplicate) { > + printf("Error in duplicates list\n"); > + return 1; > + } > + > + verbose_msg(verbose_mode, "Applying suffixes\n"); > + build_index(head); > + duplicate_iterator = duplicate; > + while (duplicate_iterator) { > + res = filter_symbols(duplicate_iterator->original_item->symb_name, > + ignore_regex, sizeof(ignore_regex) / > + sizeof(ignore_regex[0])); > + if ((res != FMATCH) && > + SYMB_NEEDS_ALIAS(duplicate_iterator->original_item)) { > + if (res < 0) > + return 1; > + > + create_suffix(duplicate_iterator->original_item->symb_name, > + new_name); > + if (!insert_after(head, duplicate_iterator->original_item->addr, > + new_name, duplicate_iterator->original_item->addr, > + duplicate_iterator->original_item->stype)) > + return 1; > + } > + > + duplicate_iterator = duplicate_iterator->next; > + } > + > + sort_list_m(&head, BY_ADDRESS); > + } > + current = head; > + while (current) { > + printf("%08lx %c %s\n", current->addr, current->stype, current->symb_name); > + current = current->next; > + } > + > + free_items(&head); > + free_duplicates(&duplicate); > + > + return 0; > +} > diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh > index a432b171be82..4e3dea3ac2df 100755 > --- a/scripts/link-vmlinux.sh > +++ b/scripts/link-vmlinux.sh > @@ -161,7 +161,11 @@ kallsyms() > fi > > info KSYMS ${2} > - scripts/kallsyms ${kallsymopt} ${1} > ${2} > + if is_enabled CONFIG_KALLSYMS_ALIAS; then > + ALIAS=".alias" > + scripts/kas_alias/kas_alias ${1} >${1}${ALIAS} > + fi > + scripts/kallsyms ${kallsymopt} ${1}${ALIAS} > ${2} > } > > # Perform one step in kallsyms generation, including temporary linking of
