On Wed, Jul 12, 2023 at 09:31:31AM +0900, Masami Hiramatsu wrote:
> On Tue, 11 Jul 2023 15:19:25 +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 tracefs 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
>
> This is a nice feature. I found one issue with padding symbols (and CFI) With
> those options, kernel will make '__cfi_' or '___pfx_' prefixed symbols for each
> function on some arch. But those generated symbols are not executed but for
> padding or storing integrity data. So you don't need to make aliases for those
> symbols.
>
> ffffffff8102c770 t __cfi_event_show
> ffffffff8102c770 t __cfi_event_show__alias__498
> ffffffff8102c780 t event_show
> ffffffff8102c780 t event_show__alias__1505
> ffffffff8102c7b0 t __cfi_umask_show
> ffffffff8102c7b0 t __cfi_umask_show__alias__736
> ffffffff8102c7c0 t umask_show
> ffffffff8102c7c0 t umask_show__alias__4217
> ffffffff8102c7f0 t __cfi_edge_show
> ffffffff8102c7f0 t __cfi_edge_show__alias__484
> ffffffff8102c800 t edge_show
> ffffffff8102c800 t edge_show__alias__1478
> ffffffff8102c830 t __cfi_inv_show
> ffffffff8102c830 t __cfi_inv_show__alias__528
> ffffffff8102c840 t inv_show
> ffffffff8102c840 t inv_show__alias__1789
> ffffffff8102c870 t __cfi_cmask_show
> ffffffff8102c870 t __cfi_cmask_show__alias__439
> ffffffff8102c880 t cmask_show
> ffffffff8102c880 t cmask_show__alias__1257
>
> Can you skip aliases for __cfi_ or __pfx_ symbols?
>
> Thank you,
>
Hi Masami,
Right, I will do that in the v2 (and I will also add the script maintainers as
suggested by steven)
Thanks!
> >
> > Signed-off-by: Alessandro Carminati (Red Hat) <alessandro.carminati@xxxxxxxxx>
> > ---
> > init/Kconfig | 17 ++
> > 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 | 112 ++++++++++++++
> > scripts/link-vmlinux.sh | 6 +-
> > 9 files changed, 483 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..a67b7b1c604b 100644
> > --- a/init/Kconfig
> > +++ b/init/Kconfig
> > @@ -1737,6 +1737,23 @@ 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.
> > +
> > +
> > # 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..d47cfec9f1f3
> > --- /dev/null
> > +++ b/scripts/kas_alias/kas_alias.c
> > @@ -0,0 +1,112 @@
> > +// 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 "item_list.h"
> > +#include "duplicates_list.h"
> > +
> > +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++);
> > +}
> > +
> > +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;
> > +
> > + 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) {
> > + 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
> >
>
>
> --
> Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
--
Alessandro Carminati (Red Hat) <alessandro.carminati@xxxxxxxxx>
