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Date:   Tue, 11 Jul 2023 12:31:47 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Alessandro Carminati <alessandro.carminati@gmail.com>
Cc:     mhiramat@kernel.org, linux-kernel@vger.kernel.org,
        linux-trace-kernel@vger.kernel.org, bristot@kernel.org,
        vmalik@redhat.com, Masahiro Yamada <masahiroy@kernel.org>,
        linux-kbuild@vger.kernel.org
Subject: Re: [PATCH] scripts/link-vmlinux.sh: Add alias to duplicate symbols
 for kallsyms
Message-ID: <20230711123147.21cfe77c@gandalf.local.home>
In-Reply-To: <20230711151925.1092080-1-alessandro.carminati@gmail.com>
References: <20230711151925.1092080-1-alessandro.carminati@gmail.com>
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I believe this should go through the build maintainer's tree.

-- Steve


On Tue, 11 Jul 2023 15:19:25 +0000
Alessandro Carminati <alessandro.carminati@gmail.com> 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
> 
> Signed-off-by: Alessandro Carminati (Red Hat) <alessandro.carminati@gmail.com>
> ---
>  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