[PATCH v2] scripts/link-vmlinux.sh: Add alias to duplicate symbols for kallsyms

Alessandro Carminati
2023-07-14T15:04:35Z

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

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@gmail.com/

Signed-off-by: Alessandro Carminati (Red Hat) <alessandro.carminati@gmail.com>
---
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(&regex, ignore_list[i], REG_EXTENDED);
+ if (res)
+ return -EREGEX;
+
+ res = regexec(&regex, symbol, 0, NULL, 0);
+ regfree(&regex);
+ 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
--
2.34.1