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Date:   Wed, 30 Aug 2023 15:00:27 +0900
From:   Masami Hiramatsu (Google) <mhiramat@kernel.org>
To:     "Alessandro Carminati (Red Hat)" <alessandro.carminati@gmail.com>
Cc:     Masami Hiramatsu <mhiramat@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Daniel Bristot de Oliveira <bristot@kernel.org>,
        Josh Poimboeuf <jpoimboe@kernel.org>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Nicolas Schier <nicolas@fjasle.eu>,
        Alexander Lobakin <aleksander.lobakin@intel.com>,
        Nick Alcock <nick.alcock@oracle.com>,
        Kris Van Hees <kris.van.hees@oracle.com>,
        Eugene Loh <eugene.loh@oracle.com>,
        Francis Laniel <flaniel@linux.microsoft.com>,
        Viktor Malik <vmalik@redhat.com>, linux-kbuild@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
        live-patching@vger.kernel.org
Subject: Re: [PATCH v3] scripts/link-vmlinux.sh: Add alias to duplicate
 symbols for kallsyms
Message-Id: <20230830150027.57bf46382eef3206c78de6d2@kernel.org>
In-Reply-To: <20230828080423.3539686-1-alessandro.carminati@gmail.com>
References: <20230828080423.3539686-1-alessandro.carminati@gmail.com>
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Hi Alessandro,

Thanks for your update!

On Mon, 28 Aug 2023 08:04:23 +0000
"Alessandro Carminati (Red Hat)" <alessandro.carminati@gmail.com> wrote:

> From: Alessandro Carminati <alessandro.carminati@gmail.com>
> 
> 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/
> 
> Changes from v2:
> - Alias tags are created by querying DWARF information from the vmlinux.
> - The filename + line number is normalized and appended to the original name.
> - The tag begins with '@' to indicate the symbol source.
> - Not a change, but worth mentioning, since the alias is added to the existing
>   list, the old duplicated name is preserved, and the livepatch way of dealing
>   with duplicates is maintained.
> - Acknowledging the existence of scenarios where inlined functions declared in
>   header files may result in multiple copies due to compiler behavior, though
>    it is not actionable as it does not pose an operational issue.
> - Highlighting a single exception where the same name refers to different
>   functions: the case of "compat_binfmt_elf.c," which directly includes
>   "binfmt_elf.c" producing identical function copies in two separate
>   modules.
> 
> sample from new v3
> 
>  ~ # cat /proc/kallsyms | grep gic_mask_irq
>  ffffd0b03c04dae4 t gic_mask_irq
>  ffffd0b03c04dae4 t gic_mask_irq@_drivers_irqchip_irq-gic_c_167
>  ffffd0b03c050960 t gic_mask_irq
>  ffffd0b03c050960 t gic_mask_irq@_drivers_irqchip_irq-gic-v3_c_404

Could you also update the sample output in the patch description?
And I can not see this line information but a serial number aliases,
is there any way to enable this file-name aliases? (LLVM is not supported?)
I think we'd better to have a new CONFIG_KALLSYMS_ALIAS_SRCLINE and
clarify what is required.

>  ~ #
> 
> https://lore.kernel.org/all/20230714150326.1152359-1-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/a2l.c             | 268 ++++++++++++++++++++++++++++
>  scripts/kas_alias/a2l.h             |  32 ++++
>  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       | 217 ++++++++++++++++++++++
>  scripts/link-vmlinux.sh             |  11 +-
>  11 files changed, 910 insertions(+), 3 deletions(-)
>  create mode 100644 scripts/kas_alias/Makefile
>  create mode 100644 scripts/kas_alias/a2l.c
>  create mode 100644 scripts/kas_alias/a2l.h
>  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..bc69fcd9cbc8 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 && (DEBUG_INFO_DWARF4 || DEBUG_INFO_DWARF5)
> +	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

You don't need 'CONFIG_' prefix here.

> +	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..e1fde69232b4
> --- /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 a2l.o
> diff --git a/scripts/kas_alias/a2l.c b/scripts/kas_alias/a2l.c
> new file mode 100644
> index 000000000000..a9692ac30180
> --- /dev/null
> +++ b/scripts/kas_alias/a2l.c
> @@ -0,0 +1,268 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <unistd.h>
> +#include <sys/types.h>
> +#include <sys/wait.h>
> +#include <string.h>
> +#include <stdint.h>
> +#include <stdbool.h>
> +
> +#include "a2l.h"
> +
> +int addr2line_pid = -1;
> +int a2l_in[2];
> +int a2l_out[2];
> +char line[MAX_BUF];
> +char vmlinux_path[MAX_BUF];
> +char addr2line_cmd[MAX_CMD_LEN];
> +FILE *a2l_stdin, *a2l_stdout;
> +
> +static char *normalize_path(const char *input_path, char *output_path)
> +{
> +	char *prev_token = NULL;
> +	char *delimiter = "/";
> +	char inbuf[MAX_BUF];
> +	char *token;
> +	char *pos;
> +
> +	memset(inbuf, 0, MAX_BUF);
> +	*output_path = '\0';
> +	strncpy(inbuf, input_path, MAX_BUF);
> +	if (!input_path || !output_path || strlen(input_path) == 0)
> +		return NULL;
> +
> +	token = strtok(inbuf, delimiter);
> +	while (token) {
> +		if (strcmp(token, "..") == 0 && prev_token) {
> +			pos = strrchr(output_path, '/');
> +			if (pos)
> +				*pos = '\0';
> +
> +		} else if (strcmp(token, ".") != 0) {
> +			strcat(output_path, "/");
> +			strcat(output_path, token);
> +		}
> +
> +		prev_token = token;
> +		token = strtok(NULL, delimiter);
> +	}
> +
> +	return output_path;
> +}
> +
> +static void path_of(const char *full_path, char *path)
> +{
> +	const char *last_slash = strrchr(full_path, '/');
> +	size_t path_length;
> +	char cwd[MAX_BUF];
> +
> +	if (!last_slash) {
> +		if (getcwd(cwd, sizeof(cwd)))
> +			strcpy(path, cwd);
> +		else
> +			strcpy(path, ".");
> +	} else {
> +		path_length = last_slash - full_path;
> +		strncpy(path, full_path, path_length);
> +		path[path_length] = '\0';
> +	}
> +}
> +
> +static bool file_exists(const char *file_path)
> +{
> +	FILE *file;
> +
> +	file = fopen(file_path, "r");
> +	if (file) {
> +		fclose(file);
> +		return true;
> +	}
> +	return false;
> +}
> +
> +int addr2line_init(const char *cmd, const char *vmlinux)
> +{
> +	if ((!file_exists(cmd)) || (!file_exists(vmlinux))) {
> +		printf("file not found\n");
> +		return 0;
> +		}

nit: mis-indentation?

> +
> +	path_of(vmlinux, vmlinux_path);
> +	if (pipe(a2l_in) == -1) {
> +		printf("Failed to create pipe\n");
> +		return 0;
> +	}
> +
> +	if (pipe(a2l_out) == -1) {
> +		printf("Failed to create pipe\n");
> +		return 0;
> +	}
> +
> +	addr2line_pid = fork();
> +	if (addr2line_pid == -1) {
> +		printf("Failed to fork process\n");
> +		close(a2l_in[P_READ]);
> +		close(a2l_in[P_WRITE]);
> +		close(a2l_out[P_READ]);
> +		close(a2l_out[P_WRITE]);
> +		return 0;
> +	}
> +
> +	if (addr2line_pid == 0) {
> +		dup2(a2l_in[P_READ], 0);
> +		dup2(a2l_out[P_WRITE], 1);
> +		close(a2l_in[P_WRITE]);
> +		close(a2l_out[P_READ]);
> +
> +		execlp(cmd, cmd, ADDR2LINE_ARGS, vmlinux, NULL);
> +
> +		printf("Failed to execute addr2line command\n");
> +		exit(1);
> +	} else {
> +		close(a2l_in[P_READ]);
> +		close(a2l_out[P_WRITE]);
> +	}
> +
> +	a2l_stdin = fdopen(a2l_in[P_WRITE], "w");
> +	if (!a2l_stdin) {
> +		printf("Failed to open pipe a2l_in\n");
> +		return 0;
> +	}
> +
> +	a2l_stdout = fdopen(a2l_out[P_READ], "r");
> +	if (!a2l_stdout) {
> +		printf("Failed to open pipe a2l_out\n");
> +		fclose(a2l_stdin);
> +		return 0;
> +	}
> +
> +	return 1;
> +}
> +
> +const char *remove_subdir(const char *home, const char *f_path)
> +{
> +	int i = 0;
> +
> +	while (*(home + i) == *(f_path + i))
> +		i++;
> +
> +	return (strlen(home) != i) ? NULL : f_path + i;
> +}
> +
> +char *addr2line_get_lines(uint64_t address)
> +{
> +	char buf[MAX_BUF];
> +
> +	fprintf(a2l_stdin, "%08lx\n", address);
> +	fflush(a2l_stdin);
> +
> +	if (!fgets(line, sizeof(line), a2l_stdout)) {
> +		printf("Failed to read lines from addr2line\n");
> +		return NULL;
> +	}
> +
> +	if (!fgets(line, sizeof(line), a2l_stdout)) {
> +		printf("Failed to read lines from addr2line\n");
> +		return NULL;
> +	}
> +
> +	line[strcspn(line, "\n")] = '\0';
> +	strncpy(buf, line, MAX_BUF);
> +	return normalize_path(buf, line);
> +}
> +
> +int addr2line_cleanup(void)
> +{
> +	int status;
> +
> +	if (addr2line_pid != -1) {
> +		kill(addr2line_pid, SIGKILL);
> +		waitpid(addr2line_pid, &status, 0);
> +		fclose(a2l_stdin);
> +		fclose(a2l_stdout);
> +		addr2line_pid = -1;
> +	}
> +
> +	return 1;
> +}
> +
> +static char *find_executable(const char *command)
> +{
> +	char *path_env = getenv("PATH");
> +	char *executable_path;
> +	char *path_copy;
> +	char *path;
> +	int n;
> +
> +	if (!path_env)
> +		return NULL;
> +
> +	path_copy = strdup(path_env);
> +	if (!path_copy)
> +		return NULL;
> +
> +	path = strtok(path_copy, ":");
> +	while (path) {
> +		n = snprintf(0, 0, "%s/%s", path, command);
> +		executable_path = (char *)malloc(n + 1);
> +		snprintf(executable_path, n + 1, "%s/%s", path, command);
> +		if (access(executable_path, X_OK) == 0) {
> +			free(path_copy);
> +			return executable_path;
> +		}
> +
> +	path = strtok(NULL, ":");
> +	free(executable_path);
> +	executable_path = NULL;

nit: mis-indentation?

> +	}
> +
> +	free(path_copy);
> +	if (executable_path)
> +		free(executable_path);
> +	return NULL;
> +}
> +
> +const char *get_addr2line(int mode)
> +{
> +	char *buf = "";
> +
> +	switch (mode) {
> +	case A2L_CROSS:
> +		buf = getenv("CROSS_COMPILE");
> +		memcpy(addr2line_cmd, buf, strlen(buf));
> +	case A2L_DEFAULT:
> +		memcpy(addr2line_cmd + strlen(buf), ADDR2LINE, strlen(ADDR2LINE));
> +		buf = find_executable(addr2line_cmd);
> +		if (buf) {
> +			memcpy(addr2line_cmd, buf, strlen(buf));
> +			free(buf);
> +		}
> +		return addr2line_cmd;
> +	case A2L_LLVM:
> +	default:
> +		return NULL;
> +	}
> +}
> +
> +char *get_vmlinux(char *input)
> +{
> +	const char *match_string1 = ".syms";
> +	const char *match_string2 = ".tmp_vmlinux.kallsyms";
> +	char *result = NULL;
> +	char *match_pos;
> +
> +	match_pos = strstr(input, match_string1);
> +	if (!match_pos)
> +		return NULL;
> +
> +	match_pos = strstr(input, match_string2);
> +	if (!match_pos)
> +		return NULL;
> +
> +	result = strdup(input);
> +	match_pos = strstr(result, match_string1);
> +	*match_pos = '\0';
> +	return result;
> +}
> diff --git a/scripts/kas_alias/a2l.h b/scripts/kas_alias/a2l.h
> new file mode 100644
> index 000000000000..ca6419229dde
> --- /dev/null
> +++ b/scripts/kas_alias/a2l.h
> @@ -0,0 +1,32 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +#ifndef A2L_H
> +#define A2L_H
> +#include <stdint.h>
> +
> +#define ADDR2LINE "addr2line"
> +#define ADDR2LINE_ARGS "-fe"
> +//#define VMLINUX "vmlinux"

Nit: this should be removed if it is not used.

> +#define MAX_BUF 4096
> +#define MAX_CMD_LEN 256
> +#define P_READ 0
> +#define P_WRITE 1
> +#define A2L_DEFAULT 1
> +#define A2L_CROSS 2
> +#define A2L_LLVM 3
> +#define A2L_MAKE_VALUE 2
> +
> +extern int addr2line_pid;
> +extern int a2l_in[2];
> +extern int a2l_out[2];
> +extern char line[MAX_BUF];
> +extern char vmlinux_path[MAX_BUF];
> +extern char addr2line_cmd[MAX_CMD_LEN];
> +
> +int addr2line_init(const char *cmd, const char *vmlinux);
> +char *addr2line_get_lines(uint64_t address);
> +int addr2line_cleanup(void);
> +const char *remove_subdir(const char *home, const char *f_path);
> +const char *get_addr2line(int mode);
> +char *get_vmlinux(char *input);
> +
> +#endif
> 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"
> +

/* The item list must be sorted. */

I think we can find the duplicated symbol without sorting the list,
but such implementation level optimization will be done later.

> +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..48f2e525592a
> --- /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..532aeb39f851
> --- /dev/null
> +++ b/scripts/kas_alias/kas_alias.c
> @@ -0,0 +1,217 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <stdint.h>
> +#include <unistd.h>
> +#include <string.h>
> +#include <stdbool.h>
> +#include <stdarg.h>
> +#include <regex.h>
> +
> +#include "item_list.h"
> +#include "duplicates_list.h"
> +#include "a2l.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 void create_file_suffix(const char *name, uint64_t address, char *output_suffix, char *cwd)
> +{
> +	const char *f_path;
> +	char *buf;
> +	int i = 0;
> +
> +	buf = addr2line_get_lines(address);
> +	f_path = remove_subdir(cwd, buf);
> +	if (f_path) {
> +		sprintf(output_suffix, "%s@%s", name, f_path);
> +		while (*(output_suffix + i) != '\0') {
> +			switch (*(output_suffix + i)) {
> +			case '/':
> +			case ':':
> +			case '.':

This is not enough because file path will accept more than that.
E.g. '+', '&', '-'. 
So I think we should check it by '!isalnum()'. (allow-list method)

> +				*(output_suffix + i) = '_';
> +				break;
> +			default:
> +			}
> +		i++;
> +		}
> +	} else {
> +		create_suffix(name, output_suffix);
> +	}
> +}
> +
> +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;
> +	}
> +
> +	if (!addr2line_init(get_addr2line(A2L_DEFAULT), get_vmlinux(argv[1])))
> +		return 1;
> +
> +	while (fscanf(fp, "%lx %c %99s\n", &address, &t, sym_name) == 3) {
> +		if (strstr(sym_name, "@_")) {
> +			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_file_suffix(duplicate_iterator->original_item->symb_name,
> +						   duplicate_iterator->original_item->addr,
> +						   new_name, vmlinux_path);
> +				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);
> +	addr2line_cleanup();
> +	return 0;
> +}
> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> index a432b171be82..cacf60b597ce 100755
> --- a/scripts/link-vmlinux.sh
> +++ b/scripts/link-vmlinux.sh
> @@ -89,8 +89,9 @@ vmlinux_link()
>  
>  	ldflags="${ldflags} ${wl}--script=${objtree}/${KBUILD_LDS}"
>  
> -	# The kallsyms linking does not need debug symbols included.
> -	if [ "$output" != "${output#.tmp_vmlinux.kallsyms}" ] ; then
> +	# The kallsyms linking does not need debug symbols included, unless the KALLSYMS_ALIAS.
> +	if [ ! is_enabled CONFIG_KALLSYMS_ALIAS ] && \
> +	    [ "$output" != "${output#.tmp_vmlinux.kallsyms}" ] ; then
>  		ldflags="${ldflags} ${wl}--strip-debug"
>  	fi
>  
> @@ -161,7 +162,11 @@ 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

Nit: wrong indentation.
And ALIAS is not defined if CONFIG_KALLSYMS_ALIAS=n.


> +	scripts/kallsyms ${kallsymopt} ${1}${ALIAS} > ${2}
>  }
>  
>  # Perform one step in kallsyms generation, including temporary linking of
> -- 
> 2.34.1
> 


Thank you,

-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>