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Date:   Wed, 25 Oct 2023 20:33:43 +0200
From:   Alessandro Carminati <alessandro.carminati@...il.com>
To:     Francis Laniel <flaniel@...ux.microsoft.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        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>,
        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 Francis,
Thanks a lot for your feedback!

Il giorno mer 25 ott 2023 alle ore 15:21 Francis Laniel
<flaniel@...ux.microsoft.com> ha scritto:
>
> 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.

Thanks, fix in the next version.

>
> > +    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.

Nice suggestion, next version will have a debug_print function.

>
> > +    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.
You're right. Last-minute change. I should check more carefully next time
before submitting.
>
> > +    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).
it was a concern I had.
I think I will add a field to the line structure to carry the int value.
Thank you for sharing your concern.
>
> > +                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?
In my original intention, this message needed to be print unconditionally.
But you're probably right, it makes more sense to print under debug
condition.
I'll make necessary adjustments in next version.
>
> > +
> > +    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".
Sure, thanks!
>
> > +    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?
Fair enough, I'll change it.
>
> > +                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?
Actually, it is a limitation of the command line buffer size.
There is no specific reason for choosing the number 50.
My only intention was to use a reasonably high number to limit the size
of the command line.
>
> > +                   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?
Not sure to understand this feedback.
>
> > +                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.
>
>
Thank you!

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