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Message-ID: <5776666.DvuYhMxLoT@pwmachine>
Date: Wed, 25 Oct 2023 16:21:17 +0300
From: Francis Laniel <flaniel@...ux.microsoft.com>
To: Masahiro Yamada <masahiroy@...nel.org>,
"Alessandro Carminati (Red Hat)" <alessandro.carminati@...il.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
Steven Rostedt <rostedt@...dmis.org>,
Daniel Bristot de Oliveira <bristot@...nel.org>,
Josh Poimboeuf <jpoimboe@...nel.org>,
Luis Chamberlain <mcgrof@...nel.org>,
Nathan Chancellor <nathan@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Nicolas Schier <nicolas@...sle.eu>,
Alexander Lobakin <aleksander.lobakin@...el.com>,
Nick Alcock <nick.alcock@...cle.com>,
Kris Van Hees <kris.van.hees@...cle.com>,
Eugene Loh <eugene.loh@...cle.com>,
Viktor Malik <vmalik@...hat.com>,
Petr Mladek <pmladek@...e.com>, Tom Rix <trix@...hat.com>,
Alessandro Carminati <alessandro.carminati@...il.com>,
linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-trace-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH v6] scripts/link-vmlinux.sh: Add alias to duplicate symbols for kallsyms
Hi!
Le mardi 24 octobre 2023, 23:11:57 EEST Alessandro Carminati (Red Hat) a
écrit :
> In the kernel environment, scenarios often arise where identical names
> are shared among symbols within core image or modules.
> While this poses no complications for the kernel's binary itself, it
> creates challenges when conducting trace or probe operations using tools
> like kprobe.
>
> A solution has been introduced, referred to as "kas_alias."
> During the kernel's build process, an extensive scan of all objects is
> performed, encompassing both core kernel components and modules, to
> collect comprehensive symbol information.
> Subsequently, for all duplicate symbolsthe process enriches symbol names
> by appending meaningful suffixes derived from source files and line
> numbers.
> These freshly generated aliases simplify interaction with symbols.
>
> The procedure is executed as follows.
> During the kernel's build phase, an exhaustive search for duplicates among
> symbols that share the same name in both kernel image and all modules
> object files.
> For the kernel core image, a new nem data file is created and alias for
> all duplicate symbols is added.
> For modules, the lib objects the ELF symtable is modified with the
> addition of the alias for the duplicate symbols.
>
> Consider the symbol "device_show", you can expect an output like the
> following:
>
> ~ # cat /proc/kallsyms | grep " device_show"
> ffffffff963cd2a0 t device_show
> ffffffff963cd2a0 t device_show@...vers_pci_pci_sysfs_c_49
> ffffffff96454b60 t device_show
> ffffffff96454b60 t device_show@...vers_virtio_virtio_c_16
> ffffffff966e1700 T device_show_ulong
> ffffffff966e1740 T device_show_int
> ffffffff966e1770 T device_show_bool
> ffffffffc04e10a0 t device_show [mmc_core]
> ffffffffc04e10a0 t device_show@...vers_mmc_core_sdio_bus_c_45 [mmc_core]
>
> Signed-off-by: Alessandro Carminati (Red Hat)
> <alessandro.carminati@...il.com>
>
> NOTE1:
> About the symbols name duplication that happens as consequence of the
> inclusion compat_binfmt_elf.c does, it is evident that this corner is
> inherently challenging the addr2line approach.
> Attempting to conceal this limitation would be counterproductive.
>
> compat_binfmt_elf.c includes directly binfmt_elf.c, addr2line can't help
> but report all functions and data declared by that file, coming from
> binfmt_elf.c.
>
> My position is that, rather than producing a more complicated pipeline
> to handle this corner case, it is better to fix the compat_binfmt_elf.c
> anomaly.
>
> This patch does not deal with the two potentially problematic symbols
> defined by compat_binfmt_elf.c
>
> NOTE2:
> The current implementation does not offer a solution for out-of-tree
> modules. My stance is that these modules fall outside the scope, but I
> welcome any comments or feedback regarding this matter.
>
> 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@gm
> ail.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.
>
> https://lore.kernel.org/all/20230714150326.1152359-1-alessandro.carminati@gm
> ail.com/
>
> Changes from v3:
> * kas_alias was rewritten in Python to create a more concise and
> maintainable codebase.
> * The previous automation process used by kas_alias to locate the vmlinux
> and the addr2line has been replaced with an explicit command-line switch
> for specifying these requirements.
> * addr2line has been added into the main Makefile.
> * A new command-line switch has been introduced, enabling users to extend
> the alias to global data names.
>
> https://lore.kernel.org/all/20230828080423.3539686-1-alessandro.carminati@gm
> ail.com/
>
> Changes from v4:
> * Fixed the O=<build dir> build issue
> * The tool halts execution upon encountering major issues, thereby ensuring
> the pipeline is interrupted.
> * A cmdline option to specify the source directory added.
> * Minor code adjusments.
> * Tested on mips32 and i386
>
> https://lore.kernel.org/all/20230919193948.465340-1-alessandro.carminati@gma
> il.com/
>
> Changes from v5:
> * Regex filter extended to all symbols
> * Alias creation extended to module objects
> * Code cleaned and commented
> * kas_alias verbose execution via KAS_ALIAS_DEBUG env variable
> * CONFIG_KALLSYMS_ALIAS_SRCLINE selects KBUILD_BUILTIN to ensure no races
> during modules build
> * Tested on x86_64, aarch64 and i386
Thank you for this new version!
I tested it and it works fine, particularly with the added information about
modules:
root@...amd64:~# grep ' name_show@' /proc/kallsyms | head -5
ffffffff810fa150 t name_show@...nel_irq_irqdesc_c_264
ffffffff815ddcd0 t name_show@...vers_pnp_card_c_186
ffffffff8171ccb0 t name_show@...vers_gpu_drm_i915_gt_sysfs_engines_c_26
ffffffff8189de00 t name_show@...vers_base_power_wakeup_stats_c_93
ffffffff81a3d140 t name_show@...vers_rtc_sysfs_c_26
I reviewed the code and only found nits.
> https://lore.kernel.org/all/20230927173516.1456594-1-alessandro.carminati@gm
> ail.com/ ---
> Makefile | 14 +-
> init/Kconfig | 22 ++
> scripts/Makefile.modfinal | 10 +-
> scripts/kas_alias.py | 545 ++++++++++++++++++++++++++++++++++++++
> scripts/link-vmlinux.sh | 26 +-
> 5 files changed, 613 insertions(+), 4 deletions(-)
> create mode 100755 scripts/kas_alias.py
>
> diff --git a/Makefile b/Makefile
> index 4f283d915e54..f2c51340fa52 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -488,6 +488,7 @@ OBJCOPY = $(LLVM_PREFIX)llvm-objcopy$
(LLVM_SUFFIX)
> OBJDUMP = $(LLVM_PREFIX)llvm-objdump$(LLVM_SUFFIX)
> READELF = $(LLVM_PREFIX)llvm-readelf$(LLVM_SUFFIX)
> STRIP = $(LLVM_PREFIX)llvm-strip$(LLVM_SUFFIX)
> +ADDR2LINE = $(LLVM_PREFIX)llvm-addr2line$(LLVM_SUFFIX)
> else
> CC = $(CROSS_COMPILE)gcc
> LD = $(CROSS_COMPILE)ld
> @@ -497,6 +498,7 @@ OBJCOPY = $(CROSS_COMPILE)objcopy
> OBJDUMP = $(CROSS_COMPILE)objdump
> READELF = $(CROSS_COMPILE)readelf
> STRIP = $(CROSS_COMPILE)strip
> +ADDR2LINE = $(CROSS_COMPILE)addr2line
> endif
> RUSTC = rustc
> RUSTDOC = rustdoc
> @@ -611,7 +613,7 @@ export RUSTC_BOOTSTRAP := 1
> export ARCH SRCARCH CONFIG_SHELL BASH HOSTCC KBUILD_HOSTCFLAGS
> CROSS_COMPILE LD CC HOSTPKG_CONFIG export RUSTC RUSTDOC RUSTFMT
> RUSTC_OR_CLIPPY_QUIET RUSTC_OR_CLIPPY BINDGEN CARGO export HOSTRUSTC
> KBUILD_HOSTRUSTFLAGS
> -export CPP AR NM STRIP OBJCOPY OBJDUMP READELF PAHOLE RESOLVE_BTFIDS LEX
> YACC AWK INSTALLKERNEL +export CPP AR NM STRIP OBJCOPY OBJDUMP READELF
> ADDR2LINE PAHOLE RESOLVE_BTFIDS LEX YACC AWK INSTALLKERNEL export PERL
> PYTHON3 CHECK CHECKFLAGS MAKE UTS_MACHINE HOSTCXX
> export KGZIP KBZIP2 KLZOP LZMA LZ4 XZ ZSTD
> export KBUILD_HOSTCXXFLAGS KBUILD_HOSTLDFLAGS KBUILD_HOSTLDLIBS
> LDFLAGS_MODULE @@ -1542,6 +1544,16 @@ KBUILD_BUILTIN := 1
> modules: vmlinux
> endif
>
> +# *.ko are usually independent of vmlinux, but
> CONFIG_KALLSYMS_ALIAS_SRCLINE +# is another exception.
> +# At the time when vmlinux is being linked, kas_alias operates on both
> vmlinux +# and modules. To prevent races with modules, kas_alias needs to
> pause operations +# while it is executed.
> +ifdef CONFIG_KALLSYMS_ALIAS_SRCLINE
> +KBUILD_BUILTIN := 1
> +modules: vmlinux
> +endif
> +
> modules: modules_prepare
>
> # Target to prepare building external modules
> diff --git a/init/Kconfig b/init/Kconfig
> index 6d35728b94b2..d45dd423e1ec 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1738,6 +1738,28 @@ 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_SRCLINE
> + bool "Produces alias for duplicated text symbols" if EXPERT
> + depends on KALLSYMS && DEBUG_INFO && !DEBUG_INFO_SPLIT
> + 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, producing alias for text
> + symbol names that include the file name and line where the symbols
> + are defined in the source code.
> +
> +config KALLSYMS_ALIAS_SRCLINE_DATA
> + bool "Produces alias also for global variables names"
> + depends on KALLSYMS_ALIAS_SRCLINE
> + help
> + Sometimes it can be useful to refer to global vars by name. Since
> + they suffer the same issue as text symbols, this config option
> + allows having aliases for global variables names too.
> +
> # end of the "standard kernel features (expert users)" menu
>
> # syscall, maps, verifier
> diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
> index b3a6aa8fbe8c..3d9756a6eb3e 100644
> --- a/scripts/Makefile.modfinal
> +++ b/scripts/Makefile.modfinal
> @@ -15,6 +15,14 @@ include $(srctree)/scripts/Makefile.lib
> # find all modules listed in modules.order
> modules := $(call read-file, $(MODORDER))
>
> +ifeq ($(KBUILD_BUILTIN),y)
> + ifeq ($(or
> $(CONFIG_DEBUG_INFO_BTF_MODULES),$(CONFIG_KALLSYMS_ALIAS_SRCLINE)),y) +
> VMLINUX_DEP := vmlinux
> + endif
> +endif
> +
> +VMLINUX_DEP ?=
> +
> __modfinal: $(modules:%.o=%.ko)
> @:
>
> @@ -55,7 +63,7 @@ if_changed_except = $(if $(call
> newer_prereqs_except,$(2))$(cmd-check), \ printf '%s\n' 'savedcmd_$@
> := $(make-cmd)' > $(dot-target).cmd, @:)
>
> # Re-generate module BTFs if either module's .ko or vmlinux changed
> -%.ko: %.o %.mod.o scripts/module.lds $(and
> $(CONFIG_DEBUG_INFO_BTF_MODULES),$(KBUILD_BUILTIN),vmlinux) FORCE +%.ko:
> %.o %.mod.o scripts/module.lds $(VMLINUX_DEP) FORCE
> +$(call if_changed_except,ld_ko_o,vmlinux)
> ifdef CONFIG_DEBUG_INFO_BTF_MODULES
> +$(if $(newer-prereqs),$(call cmd,btf_ko))
> diff --git a/scripts/kas_alias.py b/scripts/kas_alias.py
> new file mode 100755
> index 000000000000..bc930039867b
> --- /dev/null
> +++ b/scripts/kas_alias.py
> @@ -0,0 +1,545 @@
> +#!/usr/bin/env python3
> +# SPDX-License-Identifier: GPL-2.0-only
> +#
> +# Copyright (C) 2023 Red Hat, Inc. Alessandro Carminati
> <alessandro.carminati@...il.com> +#
> +# kas_alias: Adds alias to duplicate symbols for the kallsyms output.
> +
> +import os
> +import re
> +import argparse
> +import subprocess
> +from enum import Enum
> +from collections import namedtuple
> +
> +# Regex representing symbols that needs no alias
> +regex_filter = [
> + "^__compound_literal\\.[0-9]+$",
> + "^__[wm]*key\\.[0-9]+$",
> + "^_*TRACE_SYSTEM.*$",
> + "^__already_done\\.[0-9]+$",
> + "^__msg\\.[0-9]+$",
> + "^__func__\\.[0-9]+$",
> + "^CSWTCH\\.[0-9]+$",
> + "^_rs\\.[0-9]+$",
> + "^___tp_str\\.[0-9]+$",
> + "^__flags\\.[0-9]+$",
> + "^___done\\.[0-9]+$",
> + "^__print_once\\.[0-9]+$",
> + "^___once_key\\.[0-9]+$",
> + "^__pfx_.*$",
> + "^__cfi_.*$",
> + "^\\.LC[0-9]+$",
> + "^\\.L[0-9]+.[0-9]+$",
> + "^__UNIQUE_ID_.*$",
> + "^symbols\\.[0-9]+$",
> + "^_note_[0-9]+$"
> + ]
> +
> +class DebugLevel(Enum):
> + PRODUCTION = 0
> + INFO = 1
> + DEBUG_BASIC = 2
> + DEBUG_MODULES = 3
> + DEBUG_ALL = 4
> +
> +class SeparatorType:
> + def __call__(self, separator):
> + if len(separator) != 1:
> + raise argparse.ArgumentTypeError("Separator must be a single
> character") + return separator
> +
> +class Addr2LineError(Exception):
> + pass
> +
> +debug = DebugLevel.PRODUCTION
> +
> +Line = namedtuple('Line', ['address', 'type', 'name'])
> +
> +def parse_nm_lines(lines, name_occurrences=None):
> + """
> + Parses a given nm output and returns the symbol list along with a hash
> of + symbol occurrences.
> + Args:
> + lines: List of tuples representing one nm line.
> + name_occurrences: Hash having the name as key, used to count names'
> + occurrences.
> + Returns:
> + Creates a new line list proper for the nm output it parsed and,
> updates + the occurrences hash.
> + """
Nit: The triple quote is not aligned.
> + if debug >= DebugLevel.DEBUG_BASIC.value:
> + print("parse_nm_lines: parse start")
Nit: You can define a logging function which takes the debug level as first
argument and only prints if its greater or egal than
DebugLevel.DEBUG_BASIC.value.
> + if name_occurrences is None:
> + name_occurrences = {}
> +
> + symbol_list = []
> +
> + for line in lines:
> + fields = line.strip().split()
> +
> + if len(fields) >= 3:
> + address, type, name = fields[0], fields[1], '
> '.join(fields[2:]) + symbol_list.append(Line(address, type,
> name))
> + name_occurrences[name] = name_occurrences.get(name, 0) + 1
> +
> + return symbol_list, name_occurrences
> +
> +def start_addr2line_process(binary_file, addr2line_file):
> + """
> + Initializes an addr2line server process operating on the given ELF
> object. + Args:
> + binary_file: String representing the binary file name object of
> addr2line + queries.
> + addr2line_file: String representing the addr2line executable name.
> + Returns:
> + Returns addr2line process descriptor.
> + """
> + if debug >= DebugLevel.DEBUG_BASIC.value:
> + print(f"start_addr2line_process: Starting addr2line process on
> {binary_file}") +
> + try:
> + addr2line_process = subprocess.Popen([addr2line_file, '-fe',
> + binary_file],
> + stdin=subprocess.PIPE,
> + stdout=subprocess.PIPE,
> + stderr=subprocess.PIPE,
> + text=True)
> + return addr2line_process
> + except Exception as e:
> + raise SystemExit(f"Fatal: Can't start addr2line resolver: {e}")
> +
> +
> +def addr2line_fetch_address(addr2line_process, address):
> + """
> + Queries a specific address using the active addr2line process.
> + Args:
> + addr2line_process: Descriptor of the addr2line process that is wanted
> to + handle the query.
> + address: The address of the symbol that needs to be resolved.
> + Returns:
> + Returns a string representing the file and line number where the
> symbol + at the specified address has been defined. The address is
> normalized + before being returned.
> + """
> + if debug >= DebugLevel.DEBUG_ALL.value:
> + print(f"addr2line_fetch_address: Resolving {address}")
> +
> + try:
> + addr2line_process.stdin.write(address + '\n')
> + addr2line_process.stdin.flush()
> + addr2line_process.stdout.readline().strip()
> + output = addr2line_process.stdout.readline().strip()
> +
> + return os.path.normpath(output)
> + except Exception as e:
> + raise SystemExit(
> + "Fatal: Error communicating with"
> + f" the addr2line resolver: {e}."
> + )
> +
> +def process_line(line, process_data_sym, init_section_info):
> + """
> + Determines whether a duplicate item requires an alias or not.
> + Args:
> + line: nm line object that needs to be checked.
> + process_data_sym: Flag indicating that the script requires to produce
> alias + also for data symbols.
Nit: init_section_info is not documented.
> + Returns:
> + Returns true if the line needs to be processed, false otherwise.
> + """
> + if debug >= DebugLevel.DEBUG_ALL.value:
> + print(f"process_line: Processing {line.address} {line.type}
> {line.name}") +
> + # The module contains symbols that were discarded after being loaded.
> Typically, + # these symbols belong to the initialization function.
> These symbols have their + # address in the init section addresses, so
> this check prevents these symbols + # from being assigned aliases.
> + if init_section_info != None:
> + if (int(line.address, 16) >= init_section_info["address"] and
> + int(line.address, 16) <= init_section_info["address"] +
> init_section_info["size"]): + if debug >=
> DebugLevel.DEBUG_ALL.value:
Nit: You can declare the following variable:
hex_adress = int(line.address, 16)
To avoid doing the cast twice (I do not know how Python optimizes code, so
maybe this is not needed).
> + print(f"process_line: Skip {line.name} since its address is
> .init.text") + return False
> +
> + if process_data_sym:
> + return not (any(re.match(regex, line.name) for regex in
> regex_filter)) + else:
> + return (line.type in {"T", "t"}) and (
> + not (any(re.match(regex, line.name) for regex in
> regex_filter))) +
> +def fetch_file_lines(filename):
> + """
> + Reads a text file and retrieves its content.
> + Args:
> + filename: String representing the name of the file that needs to be
> read. + Returns:
> + Returns a string list representing the lines read in the file.
> + """
> + if debug >= DebugLevel.DEBUG_BASIC.value:
> + print(f"fetch_file_lines: Fetch {filename}")
> +
> + try:
> + with open(filename, 'r') as file:
> + lines = [line.strip() for line in file.readlines()]
> + return lines
> + except FileNotFoundError:
> + raise SystemExit(f"Fatal: File not found: {filename}")
> +
> +def do_nm(filename, nm_executable):
> + """
> + Runs the nm command on a specified file.
> + Args:
> + filename: String representing the name of the file on which nm should
> + run against.
> + nm_executable: String representing the nm executable filename.
> + Returns:
> + Returns a strings list representing the nm output.
> + """
> + # Later, during processing, objcopy cannot modify files in place when
> + # adding new alias symbols. It requires a source file and a destination
> + # file.
> + # After this operation, there is an object file ".o" with the aliases
> and + # a ".k{0,1}o.orig" file, which is the old intended object and
> serves as the + # source for objcopy.
> + # In a fresh build, the state is just fine.
> + # However, in a second build without clean, an issue arises.
> + # The ".k{0,1}o" file already contain the alias, and reprocessing it,
> do + # corrupt the final result. To address this, do_nm must check if
> the file + # ".k{0,1}o.orig" already exists.
> + # If it does, that's the target for nm and must be renamed in
> ".k{0,1}o" + # to restore the intended state. If not, it's a fresh
> build, and nm can + # proceed with the ".k{0,1}o" file.
> + backup_file = filename + '.orig'
> + if os.path.exists(backup_file):
> + print(f"do_nm: {filename} is not clean, restore {backup_file} to
> {filename}") + os.rename(backup_file, filename)
Nit: Should the print be done conditionally on debug level?
> +
> + if debug >= DebugLevel.DEBUG_BASIC.value:
> + print(f"do_nm: executing {nm_executable} -n {filename}")
> +
> + try:
> + nm_output = subprocess.check_output([nm_executable, '-n',
> filename], + universal_newlines=True,
> stderr=subprocess.STDOUT).splitlines() + return nm_output
> + except subprocess.CalledProcessError as e:
> + raise SystemExit(f"Fatal: Error executing nm: {e}")
> +
> +def make_objcpy_arg(line, decoration, elf_section_names):
> + """
> + Produces an objcopy argument statement for a single alias to be added
> in a + module.
> + Args:
> + line: nm line object target for this iteration.
> + decoration: String representing the decoration (normalized addr2line
> + output) to be added at the symbol name to have the alias.
> + elf_section_names: List of the section names that can be used by
> objcopy + to add a symbol to the ELF symbol table.
> + Returns:
> + Returns a string that directly maps the argument string objcopy
> should + use to add the alias.
> + """
> + try:
> + section = (
> + elf_section_names[".text"] if line.type.upper() == "T" else (
> + elf_section_names[".data"] if line.type.upper() == "D" else
> ( + elf_section_names[".rodata"] if line.type.upper() ==
> "R" else ".bss" + )
> + )
> + )
> + flag = "global" if line.type.isupper() else "local"
> +
> + if debug >= DebugLevel.DEBUG_MODULES.value:
> + print("make_objcpy_arg: "
> + f"{line.name +
> decoration}={section}:0x{line.address},{flag}") +
> +
> + return (
> + "--add-symbol "
> + f"{line.name +
> decoration}={section}:0x{line.address},{flag} " + )
> + except Exception:
> + print(
> + f"make_objcpy_arg warning: Skip alias for {line.name}"
> + f" type {line.type} because no corresponding section found.")
> + return ""
> +
> +def execute_objcopy(objcopy_executable, objcopy_args, object_file):
> + """
> + Uses objcopy to add aliases to a given module object file.
> + Since objcopy can't operate in place, the original object file is
> renamed + before operating on it. At function end, a new object file
> having the old + object's name is carrying the aliases for the duplicate
> symbols. + Args:
> + objcopy_executable: String representing the object copy executable
> file. + objcopy_args: Arguments (aliases to add to the object file) to
> be used + in the objcopy execution command line.
> + object_file: Target object file (module object file) against which
> objcopy is executed. + Returns:
> + Nothing is returned, but as a side effect of this function execution,
> + the module's object file contains the aliases for duplicated
> symbols. + """
> + # Rename the original object file by adding a suffix
> + backup_file = object_file + '.orig'
> + if debug >= DebugLevel.DEBUG_MODULES.value:
> + print("execute_objcopy: "
> + f"rename {object_file} to {backup_file}")
> + os.rename(object_file, backup_file)
> +
> + full_command = (
> + f"{objcopy_executable} "
> + f"{objcopy_args} {backup_file} {object_file}"
> + )
> + if debug >= DebugLevel.DEBUG_MODULES.value:
> + print(f"execute_objcopy: executing {full_command}")
> +
> + try:
> + subprocess.run(full_command, shell=True, check=True)
> + except subprocess.CalledProcessError as e:
> + os.rename(backup_file, object_file)
> + raise SystemExit(f"Fatal: Error executing objcopy: {e}")
> +
> +def generate_decoration(line, config, addr2line_process):
> + """
> + Generates symbol decoration to be used to make the alias name, by
> + querying addr2line.
> + Args:
> + line: nm line object that needs an alias.
> + config: Object containing command line configuration.
> + addr2line_process: Descriptor of the addr2line process that serves
> + the binary object where the symbol belongs.
> + Returns:
> + Returns a string representing the decoration for the given symbol,
> + or empty string if this can not be done. E.g., addr2line can't find
> + the point where the symbol is defined.
> + """
> + output = addr2line_fetch_address(addr2line_process, line.address)
> + decoration = config.separator + "".join(
> + "_" if not c.isalnum() else c for c in
> output.replace(config.linux_base_dir, "") + )
> + # The addr2line can emit the special string "?:??" when addr2line can
> not find the + # specified address in the DWARF section that after
> normalization it becomes "____". + # In such cases, emitting an alias
> wouldn't make sense, so it is skipped. + if decoration !=
> config.separator + "____":
> + return decoration
> + return ""
> +
> +def get_objdump_text(objdump_executable, file_to_operate):
> + """
> + objdump output is needed for a couple of functions revolving around
> + modules. This function kust query objdump to emit sections info and
Nit: "This function just queries".
> + return its output.
> + Args:
> + objdump_executable: String representing the objdump executable.
> + file_to_operate: file whose section names are wanted.
> + Returns:
> + Returns objdump output.
> + """
> + try:
> + output = subprocess.check_output(
> + [objdump_executable, '-h', file_to_operate],
> + universal_newlines=True)
> +
> + except Exception as e:
> + raise SystemExit(
> + "Fatal: Can't find section names"
> + f" for {file_to_operate}. Error: {e}"
> + )
> + return output
> +
> +def get_init_text_info(objdump_lines):
> + """
> + Recovers info on the .init.text section.
> + Args:
> + objdump_lines: output from objdump -h command.
> + Returns:
> + Returns a map containing the size and address of the .init.text
> section + None if it is not there.
> + """
> + section_info = None
> + section_name_pattern = re.compile(r'^\s*\d+')
> +
> + for line in objdump_lines.strip().splitlines():
> + if section_name_pattern.match(line):
> + parts = line.split()
> + if len(parts) >= 2:
> + current_section_name = parts[1]
> + if current_section_name == ".init.text":
> + size = int(parts[2], 16)
> + address = int(parts[3], 16)
> + section_info = {"size": size, "address": address}
> + break
> +
> + return section_info
> +
> +def get_section_names(objdump_lines):
> + """
> + objcopy needs to refer to a section name to assign the symbol type.
> + Unfortunately, not always all the section are present into a given
> + object file exist, for example, ".rodata" can not exist, and a [Rr]
> + symbol my refer to some other section e.g., ".rodata.str1".
> + For this reason this function tries to recover the exact names to use
> + in an objcopy statement.
> + Args:
> + objdump_lines: output from objdump -h command.
> + Returns:
> + Returns a map containing four string indexed with typical section
> + names.
> + """
> + section_names = []
> + lines = objdump_lines.strip().splitlines()
> + section_name_pattern = re.compile(r'^\s*\d+')
> + for line in lines:
> + if section_name_pattern.match(line):
> + parts = line.split()
> + if len(parts) >= 2:
> + section_name = parts[1]
> + section_names.append(section_name)
> +
> + best_matches = [".text", ".rodata", ".data", ".bss"]
> + result = {}
> +
> + for match in best_matches:
> + for section_name in section_names:
> + if re.match(match+".*", section_name):
Nit: Is a regex needed? Or simply checking the section_name contains the
string is OK?
> + result[match] = section_name
> +
> + if debug >= DebugLevel.DEBUG_MODULES.value:
> + for key, value in result.items():
> + print(f"get_section_names: sections {key} = {value}")
> +
> + return result
> +
> +def produce_output_modules(config, symbol_list, name_occurrences,
> + module_file_name, addr2line_process):
> + """
> + Computes the alias addition on a given module object file.
> + Args:
> + config: Object containing command line configuration.
> + symbol_list: List of tuples representing nm lines for the given
> object + file.
> + name_occurrences: Hash that stores symbol occurreces for the build.
> + module_file_name: String representing the target moule object file.
> + addr2line_process: Descriptor of the addr2line process that is wanted
> to + handle the query.
> + Returns:
> + Nothing is returned, but as a side effect of this function execution,
> + the module's object file contains the aliases for duplicated
> symbols. + """
> + objcopy_args = "";
> + args_cnt = 0
> + objdump_data = get_objdump_text(config.objdump_file, module_file_name)
> + elf_section_names = get_section_names(objdump_data)
> + init_text_section_data = get_init_text_info(objdump_data)
> + for obj in symbol_list:
> + if (name_occurrences[obj.name] > 1) and process_line(obj,
> config.process_data_sym, init_text_section_data): + decoration =
> generate_decoration(obj, config, addr2line_process) + if
> decoration != "":
> + objcopy_args = objcopy_args + make_objcpy_arg(obj,
> decoration, elf_section_names) + args_cnt = args_cnt + 1
> + if args_cnt > 50:
Is this a limitation of objcopy?
> + if debug >= DebugLevel.DEBUG_MODULES.value:
> + print("Produce_output_modules: Number of arguments
> high, split objcopy call into multiple statements.") +
> execute_objcopy(config.objcopy_file, objcopy_args, module_file_name) +
> args_cnt = 0
> + objcopy_args = ""
> +
> + execute_objcopy(config.objcopy_file, objcopy_args, module_file_name)
> +
> +def produce_output_vmlinux(config, symbol_list, name_occurrences,
> addr2line_process): + """
> + Computes the alias addition for the core Linux on image.
> + Args:
> + config: Object containing command line configuration.
> + symbol_list: List of tuples representing nm lines for the given
> object + file.
> + name_occurrences: Hash that stores symbol occurreces for the build.
> + addr2line_process: Descriptor of the addr2line process that is wanted
> to + handle the query.
> + Returns:
> + Nothing is returned, but as a side effect of this function execution,
> + the core kernel image contains the aliases for duplicated symbols. +
> """
> + with open(config.output_file, 'w') as output_file:
> + for obj in symbol_list:
> + output_file.write(f"{obj.address} {obj.type} {obj.name}\n")
> + if (name_occurrences[obj.name] > 1) and process_line(obj,
> config.process_data_sym, None): + decoration =
> generate_decoration(obj, config, addr2line_process) + if
> decoration != "":
> + output_file.write(f"{obj.address} {obj.type} {obj.name
> + decoration}\n") +
> +if __name__ == "__main__":
> + # Handles command-line arguments and generates a config object
> + parser = argparse.ArgumentParser(description='Add alias to multiple
> occurring symbols name in kallsyms') + parser.add_argument('-a',
> "--addr2line", dest="addr2line_file", required=True, help="Set the
> addr2line executable to be used.") + parser.add_argument('-b',
> "--basedir", dest="linux_base_dir", required=True, help="Set base directory
> of the source kernel code.") + parser.add_argument('-c', "--objcopy",
> dest="objcopy_file", required=True, help="Set the objcopy executable to be
> used.") + parser.add_argument('-d', "--process_data",
> dest="process_data_sym", required=False, help="Requires the tool to process
> data symbols along with text symbols.", action='store_true') +
> parser.add_argument('-e', "--nm", dest="nm_file", required=True, help="Set
> the nm executable to be used.") + parser.add_argument('-m',
> "--modules_list", dest="module_list", required=True, help="Set the file
> containing the list of the modules object files.") +
> parser.add_argument('-n', "--nmdata", dest="nm_data_file", required=True,
> help="Set vmlinux nm output file to use for core image.") +
> parser.add_argument('-o', "--outfile", dest="output_file", required=True,
> help="Set the vmlinux nm output file containing aliases.") +
> parser.add_argument('-s', "--separator", dest="separator", required=False,
> help="Set separator, character that separates original name from the
> addr2line data in alias symbols.", default="@", type=SeparatorType()) +
> parser.add_argument('-u', "--objdump", dest="objdump_file", required=True,
> help="Set objdump executable to be used.") + parser.add_argument('-v',
> "--vmlinux", dest="vmlinux_file", required=True, help="Set the vmlinux core
> image file.") + parser.add_argument('-z', "--debug", dest="debug",
> required=False, help="Set the debug level.", choices=[f"{level.value}" for
> level in DebugLevel], default="1" ) + config = parser.parse_args()
> + debug = int(config.debug)
> +
> + try:
> + if debug >= DebugLevel.INFO.value:
> + print("kas_alias: Start processing")
> +
> + # Determine kernel source code base directory
> + config.linux_base_dir = os.path.normpath(os.getcwd() + "/" +
> config.linux_base_dir) + "/" +
> + if debug >= DebugLevel.INFO.value:
> + print("kas_alias: Process nm data from vmlinux")
> +
> + # Process nm data from vmlinux
> + vmlinux_nm_lines = fetch_file_lines(config.nm_data_file)
> + vmlinux_symbol_list, name_occurrences =
> parse_nm_lines(vmlinux_nm_lines) +
> + if debug >= DebugLevel.INFO.value:
> + print("kas_alias: Process nm data for modules")
> +
> + # Process nm data for modules
> + module_list = fetch_file_lines(config.module_list)
> + module_symbol_list = {}
> + for module in module_list:
> + module_nm_lines = do_nm(module, config.nm_file)
> + module_symbol_list[module], name_occurrences =
> parse_nm_lines(module_nm_lines, name_occurrences) +
> + if debug >= DebugLevel.INFO.value:
> + print("kas_alias: Produce file for vmlinux")
> +
> + # Produce file for vmlinux
> + addr2line_process = start_addr2line_process(config.vmlinux_file,
> config.addr2line_file) + produce_output_vmlinux(config,
> vmlinux_symbol_list, name_occurrences, addr2line_process) +
> addr2line_process.stdin.close()
> + addr2line_process.stdout.close()
> + addr2line_process.stderr.close()
> + addr2line_process.wait()
> +
> + # link-vmlinux.sh calls this two times: Avoid running kas_alias
> twice for efficiency and prevent duplicate aliases + # in module
> processing by checking the last letter of the nm data file + if
> config.vmlinux_file and config.vmlinux_file[-1] == '2': + if
> debug >= DebugLevel.INFO.value:
Shouldn't this rather test nmdata?
> + print("kas_alias: Add aliases to module files")
> +
> + # Add aliases to module files
> + for module in module_list:
> + addr2line_process = start_addr2line_process(module,
> config.addr2line_file) + produce_output_modules(config,
> module_symbol_list[module], name_occurrences, module, addr2line_process) +
> addr2line_process.stdin.close()
> + addr2line_process.stdout.close()
> + addr2line_process.stderr.close()
> + addr2line_process.wait()
> + else:
> + if debug >= DebugLevel.INFO.value:
> + print("kas_alias: Skip module processing if pass is not the
> second") +
> +
> + except Exception as e:
> + raise SystemExit(f"Script terminated due to an error: {e}")
> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> index a432b171be82..beb94f1f7961 100755
> --- a/scripts/link-vmlinux.sh
> +++ b/scripts/link-vmlinux.sh
> @@ -91,7 +91,12 @@ vmlinux_link()
>
> # The kallsyms linking does not need debug symbols included.
> if [ "$output" != "${output#.tmp_vmlinux.kallsyms}" ] ; then
> - ldflags="${ldflags} ${wl}--strip-debug"
> + # The kallsyms linking does not need debug symbols included,
> + # unless the KALLSYMS_ALIAS_SRCLINE.
> + if ! is_enabled CONFIG_KALLSYMS_ALIAS_SRCLINE && \
> + [ "$output" != "${output#.tmp_vmlinux.kallsyms}" ] ; then
> + ldflags="${ldflags} ${wl}--strip-debug"
> + fi
> fi
>
> if is_enabled CONFIG_VMLINUX_MAP; then
> @@ -161,7 +166,23 @@ kallsyms()
> fi
>
> info KSYMS ${2}
> - scripts/kallsyms ${kallsymopt} ${1} > ${2}
> + ALIAS=""
> + KAS_DATA=""
> + if is_enabled CONFIG_KALLSYMS_ALIAS_SRCLINE_DATA; then
> + KAS_DATA="--process_data"
> + fi
> + if is_enabled CONFIG_KALLSYMS_ALIAS_SRCLINE; then
> + ALIAS=".alias"
> + # You can use KAS_ALIAS_DEBUG=<debug level> in the make
statements to
> enable + # verbose execution for kas_alias.
> + ${srctree}/scripts/kas_alias.py \
> + --addr2line ${ADDR2LINE} --vmlinux ${kallsyms_vmlinux} \
> + --nmdata ${1} --outfile ${1}${ALIAS} \
> + --modules_list ${MODORDER} --nm ${NM} --debug $
{KAS_ALIAS_DEBUG:-0}\
> + --objdump ${OBJDUMP} --objcopy ${OBJCOPY} \
> + --basedir ${srctree} --separator @ ${KAS_DATA}
> + fi
> + scripts/kallsyms ${kallsymopt} ${1}${ALIAS} > ${2}
> }
>
> # Perform one step in kallsyms generation, including temporary linking of
> @@ -203,6 +224,7 @@ cleanup()
> rm -f System.map
> rm -f vmlinux
> rm -f vmlinux.map
> + find . -type f -name "*.orig" -exec rm {} \;
> }
>
> # Use "make V=1" to debug this script
Best regards.
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