Re: [PATCH] scripts: remove namespace.pl

From: Masahiro Yamada
Date: Sat Oct 10 2020 - 01:52:01 EST

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In reply to: Jakub Kicinski: "Re: [PATCH] scripts: remove namespace.pl"
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On Sat, Oct 10, 2020 at 9:20 AM Jacob Keller <jacob.e.keller@xxxxxxxxx> wrote:
>
> namespace.pl is intended to help locate symbols which are defined but
> are not used externally. The goal is to avoid bloat of the namespace in
> the resulting kernel image.
>
> The script relies on object data, and only finds unused symbols for the
> configuration used to generate that object data. This results in a lot
> of false positive warnings such as symbols only used by a single
> architecture, or symbols which are used externally only under certain
> configurations.
>
> Running namespace.pl using allyesconfig, allmodconfig, and
> x86_64_defconfig yields the following results:
>
> * allmodconfig
> * 11122 unique symbol names with no external reference
> * 1194 symbols listed as multiply defined
> * 214 symbols it can't resolve
> * allyesconfig
> * 10997 unique symbol names with no external reference
> * 1194 symbols listed as multiply defined
> * 214 symbols it can't resolve
> * x86_64_defconfig
> * 5757 unique symbol names with no external reference
> * 528 symbols listed as multiply defined
> * 154 symbols it can't resolve
>
> The script also has no way to easily limit the scope of the checks to
> a given subset of the kernel, such as only checking for symbols defined
> within a module or subsystem.
>
> Discussion on public mailing lists seems to indicate that many view the
> tool output as suspect or not very useful (see discussions at [1] and
> [2] for further context).
>
> As described by Masahiro Yamada at [2], namespace.pl provides 3 types of
> checks: listing multiply defined symbols, resolving external symbols,
> and warnings about symbols with no reference.
>
> The first category of issues is easily caught by the linker as any set
> of multiply defined symbols should fail to link. The second category of
> issues is also caught by linking, as undefined symbols would cause
> issues. Even with modules, these types of issues where a module relies
> on an external symbol are caught by modpost.
>
> The remaining category of issues reported is the list of symbols with no
> external reference, and is the primary motivation of this script.
> However, it ought to be clear from the above examples that the output is
> difficult to sort through. Even allyesconfig has ~10000 entries.
>
> The current submit-checklist indicates that patches ought to go through
> namespacecheck and fix any new issues arising. But that itself presents
> problems. As described at [1], many cases of reports are due to
> configuration where a function is used externally by some configuration
> settings. Prominent maintainers appear to dislike changes modify code
> such that symbols become static based on CONFIG_* flags ([3], and [4])
>
> One possible solution is to adjust the advice and indicate that we only
> care about the output of namespacecheck on allyesconfig or allmodconfig
> builds...
>
> However, given the discussion at [2], I suspect that few people are
> actively using this tool. It doesn't have a maintainer in the
> MAINTAINERS flie, and it produces so many warnings for unused symbols
> that it is difficult to use effectively. Thus, I propose we simply
> remove it.
>
> [1] https://lore.kernel.org/netdev/20200708164812.384ae8ea@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
> [2] https://lore.kernel.org/lkml/20190129204319.15238-1-jacob.e.keller@xxxxxxxxx/
> [3] https://lore.kernel.org/netdev/20190828.154744.2058157956381129672.davem@xxxxxxxxxxxxx/
> [4] https://lore.kernel.org/netdev/20190827210928.576c5fef@xxxxxxxxxxxxxxxxxxxx/
>
> Signed-off-by: Jacob Keller <jacob.e.keller@xxxxxxxxx>
> Acked-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
> Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
> Cc: Jakub Kicinski <kuba@xxxxxxxxxx>

Applied to linux-kbuild.
Thanks.

> ---
> Documentation/process/submit-checklist.rst | 3 +-
> Makefile | 6 +-
> scripts/namespace.pl | 473 ---------------------
> 3 files changed, 2 insertions(+), 480 deletions(-)
> delete mode 100755 scripts/namespace.pl
>
> diff --git a/Documentation/process/submit-checklist.rst b/Documentation/process/submit-checklist.rst
> index 3f8e9d5d95c2..e201a6033469 100644
> --- a/Documentation/process/submit-checklist.rst
> +++ b/Documentation/process/submit-checklist.rst
> @@ -49,8 +49,7 @@ and elsewhere regarding submitting Linux kernel patches.
>
> 9) Check cleanly with sparse.
>
> -10) Use ``make checkstack`` and ``make namespacecheck`` and fix any problems
> - that they find.
> +10) Use ``make checkstack`` and fix any problems that it finds.
>
> .. note::
>
> diff --git a/Makefile b/Makefile
> index f84d7e4ca0be..a1684a4035d1 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1565,7 +1565,6 @@ help:
> echo ''
> @echo 'Static analysers:'
> @echo ' checkstack - Generate a list of stack hogs'
> - @echo ' namespacecheck - Name space analysis on compiled kernel'
> @echo ' versioncheck - Sanity check on version.h usage'
> @echo ' includecheck - Check for duplicate included header files'
> @echo ' export_report - List the usages of all exported symbols'
> @@ -1826,7 +1825,7 @@ nsdeps: modules
> # Scripts to check various things for consistency
> # ---------------------------------------------------------------------------
>
> -PHONY += includecheck versioncheck coccicheck namespacecheck export_report
> +PHONY += includecheck versioncheck coccicheck export_report
>
> includecheck:
> find $(srctree)/* $(RCS_FIND_IGNORE) \
> @@ -1841,9 +1840,6 @@ versioncheck:
> coccicheck:
> $(Q)$(BASH) $(srctree)/scripts/$@
>
> -namespacecheck:
> - $(PERL) $(srctree)/scripts/namespace.pl
> -
> export_report:
> $(PERL) $(srctree)/scripts/export_report.pl
>
> diff --git a/scripts/namespace.pl b/scripts/namespace.pl
> deleted file mode 100755
> index 1da7bca201a4..000000000000
> --- a/scripts/namespace.pl
> +++ /dev/null
> @@ -1,473 +0,0 @@
> -#!/usr/bin/env perl
> -#
> -# namespace.pl. Mon Aug 30 2004
> -#
> -# Perform a name space analysis on the linux kernel.
> -#
> -# Copyright Keith Owens <kaos@xxxxxxxxxx>. GPL.
> -#
> -# Invoke by changing directory to the top of the kernel object
> -# tree then namespace.pl, no parameters.
> -#
> -# Tuned for 2.1.x kernels with the new module handling, it will
> -# work with 2.0 kernels as well.
> -#
> -# Last change 2.6.9-rc1, adding support for separate source and object
> -# trees.
> -#
> -# The source must be compiled/assembled first, the object files
> -# are the primary input to this script. Incomplete or missing
> -# objects will result in a flawed analysis. Compile both vmlinux
> -# and modules.
> -#
> -# Even with complete objects, treat the result of the analysis
> -# with caution. Some external references are only used by
> -# certain architectures, others with certain combinations of
> -# configuration parameters. Ideally the source should include
> -# something like
> -#
> -# #ifndef CONFIG_...
> -# static
> -# #endif
> -# symbol_definition;
> -#
> -# so the symbols are defined as static unless a particular
> -# CONFIG_... requires it to be external.
> -#
> -# A symbol that is suffixed with '(export only)' has these properties
> -#
> -# * It is global.
> -# * It is marked EXPORT_SYMBOL or EXPORT_SYMBOL_GPL, either in the same
> -# source file or a different source file.
> -# * Given the current .config, nothing uses the symbol.
> -#
> -# The symbol is a candidate for conversion to static, plus removal of the
> -# export. But be careful that a different .config might use the symbol.
> -#
> -#
> -# Name space analysis and cleanup is an iterative process. You cannot
> -# expect to find all the problems in a single pass.
> -#
> -# * Identify possibly unnecessary global declarations, verify that they
> -# really are unnecessary and change them to static.
> -# * Compile and fix up gcc warnings about static, removing dead symbols
> -# as necessary.
> -# * make clean and rebuild with different configs (especially
> -# CONFIG_MODULES=n) to see which symbols are being defined when the
> -# config does not require them. These symbols bloat the kernel object
> -# for no good reason, which is frustrating for embedded systems.
> -# * Wrap config sensitive symbols in #ifdef CONFIG_foo, as long as the
> -# code does not get too ugly.
> -# * Repeat the name space analysis until you can live with with the
> -# result.
> -#
> -
> -use warnings;
> -use strict;
> -use File::Find;
> -use File::Spec;
> -
> -my $nm = ($ENV{'NM'} || "nm") . " -p";
> -my $objdump = ($ENV{'OBJDUMP'} || "objdump") . " -s -j .comment";
> -my $srctree = File::Spec->curdir();
> -my $objtree = File::Spec->curdir();
> -$srctree = File::Spec->rel2abs($ENV{'srctree'}) if (exists($ENV{'srctree'}));
> -$objtree = File::Spec->rel2abs($ENV{'objtree'}) if (exists($ENV{'objtree'}));
> -
> -if ($#ARGV != -1) {
> - print STDERR "usage: $0 takes no parameters\n";
> - die("giving up\n");
> -}
> -
> -my %nmdata = (); # nm data for each object
> -my %def = (); # all definitions for each name
> -my %ksymtab = (); # names that appear in __ksymtab_
> -my %ref = (); # $ref{$name} exists if there is a true external reference to $name
> -my %export = (); # $export{$name} exists if there is an EXPORT_... of $name
> -
> -my %nmexception = (
> - 'fs/ext3/bitmap' => 1,
> - 'fs/ext4/bitmap' => 1,
> - 'arch/x86/lib/thunk_32' => 1,
> - 'arch/x86/lib/cmpxchg' => 1,
> - 'arch/x86/vdso/vdso32/note' => 1,
> - 'lib/irq_regs' => 1,
> - 'usr/initramfs_data' => 1,
> - 'drivers/scsi/aic94xx/aic94xx_dump' => 1,
> - 'drivers/scsi/libsas/sas_dump' => 1,
> - 'lib/dec_and_lock' => 1,
> - 'drivers/ide/ide-probe-mini' => 1,
> - 'usr/initramfs_data' => 1,
> - 'drivers/acpi/acpia/exdump' => 1,
> - 'drivers/acpi/acpia/rsdump' => 1,
> - 'drivers/acpi/acpia/nsdumpdv' => 1,
> - 'drivers/acpi/acpia/nsdump' => 1,
> - 'arch/ia64/sn/kernel/sn2/io' => 1,
> - 'arch/ia64/kernel/gate-data' => 1,
> - 'security/capability' => 1,
> - 'fs/ntfs/sysctl' => 1,
> - 'fs/jfs/jfs_debug' => 1,
> -);
> -
> -my %nameexception = (
> - 'mod_use_count_' => 1,
> - '__initramfs_end' => 1,
> - '__initramfs_start' => 1,
> - '_einittext' => 1,
> - '_sinittext' => 1,
> - 'kallsyms_names' => 1,
> - 'kallsyms_num_syms' => 1,
> - 'kallsyms_addresses'=> 1,
> - 'kallsyms_offsets' => 1,
> - 'kallsyms_relative_base'=> 1,
> - '__this_module' => 1,
> - '_etext' => 1,
> - '_edata' => 1,
> - '_end' => 1,
> - '__bss_start' => 1,
> - '_text' => 1,
> - '_stext' => 1,
> - '__gp' => 1,
> - 'ia64_unw_start' => 1,
> - 'ia64_unw_end' => 1,
> - '__init_begin' => 1,
> - '__init_end' => 1,
> - '__bss_stop' => 1,
> - '__nosave_begin' => 1,
> - '__nosave_end' => 1,
> - 'pg0' => 1,
> - 'vdso_enabled' => 1,
> - '__stack_chk_fail' => 1,
> - 'VDSO32_PRELINK' => 1,
> - 'VDSO32_vsyscall' => 1,
> - 'VDSO32_rt_sigreturn'=>1,
> - 'VDSO32_sigreturn' => 1,
> -);
> -
> -
> -&find(\&linux_objects, '.'); # find the objects and do_nm on them
> -&list_multiply_defined();
> -&resolve_external_references();
> -&list_extra_externals();
> -
> -exit(0);
> -
> -sub linux_objects
> -{
> - # Select objects, ignoring objects which are only created by
> - # merging other objects. Also ignore all of modules, scripts
> - # and compressed. Most conglomerate objects are handled by do_nm,
> - # this list only contains the special cases. These include objects
> - # that are linked from just one other object and objects for which
> - # there is really no permanent source file.
> - my $basename = $_;
> - $_ = $File::Find::name;
> - s:^\./::;
> - if (/.*\.o$/ &&
> - ! (
> - m:/built-in.a$:
> - || m:arch/x86/vdso/:
> - || m:arch/x86/boot/:
> - || m:arch/ia64/ia32/ia32.o$:
> - || m:arch/ia64/kernel/gate-syms.o$:
> - || m:arch/ia64/lib/__divdi3.o$:
> - || m:arch/ia64/lib/__divsi3.o$:
> - || m:arch/ia64/lib/__moddi3.o$:
> - || m:arch/ia64/lib/__modsi3.o$:
> - || m:arch/ia64/lib/__udivdi3.o$:
> - || m:arch/ia64/lib/__udivsi3.o$:
> - || m:arch/ia64/lib/__umoddi3.o$:
> - || m:arch/ia64/lib/__umodsi3.o$:
> - || m:arch/ia64/scripts/check_gas_for_hint.o$:
> - || m:arch/ia64/sn/kernel/xp.o$:
> - || m:boot/bbootsect.o$:
> - || m:boot/bsetup.o$:
> - || m:/bootsect.o$:
> - || m:/boot/setup.o$:
> - || m:/compressed/:
> - || m:drivers/cdrom/driver.o$:
> - || m:drivers/char/drm/tdfx_drv.o$:
> - || m:drivers/ide/ide-detect.o$:
> - || m:drivers/ide/pci/idedriver-pci.o$:
> - || m:drivers/media/media.o$:
> - || m:drivers/scsi/sd_mod.o$:
> - || m:drivers/video/video.o$:
> - || m:fs/devpts/devpts.o$:
> - || m:fs/exportfs/exportfs.o$:
> - || m:fs/hugetlbfs/hugetlbfs.o$:
> - || m:fs/msdos/msdos.o$:
> - || m:fs/nls/nls.o$:
> - || m:fs/ramfs/ramfs.o$:
> - || m:fs/romfs/romfs.o$:
> - || m:fs/vfat/vfat.o$:
> - || m:init/mounts.o$:
> - || m:^modules/:
> - || m:net/netlink/netlink.o$:
> - || m:net/sched/sched.o$:
> - || m:/piggy.o$:
> - || m:^scripts/:
> - || m:sound/.*/snd-:
> - || m:^.*/\.tmp_:
> - || m:^\.tmp_:
> - || m:/vmlinux-obj.o$:
> - || m:^tools/:
> - )
> - ) {
> - do_nm($basename, $_);
> - }
> - $_ = $basename; # File::Find expects $_ untouched (undocumented)
> -}
> -
> -sub do_nm
> -{
> - my ($basename, $fullname) = @_;
> - my ($source, $type, $name);
> - if (! -e $basename) {
> - printf STDERR "$basename does not exist\n";
> - return;
> - }
> - if ($fullname !~ /\.o$/) {
> - printf STDERR "$fullname is not an object file\n";
> - return;
> - }
> - ($source = $basename) =~ s/\.o$//;
> - if (-e "$source.c" || -e "$source.S") {
> - $source = File::Spec->catfile($objtree, $File::Find::dir, $source)
> - } else {
> - $source = File::Spec->catfile($srctree, $File::Find::dir, $source)
> - }
> - if (! -e "$source.c" && ! -e "$source.S") {
> - # No obvious source, exclude the object if it is conglomerate
> - open(my $objdumpdata, "$objdump $basename|")
> - or die "$objdump $fullname failed $!\n";
> -
> - my $comment;
> - while (<$objdumpdata>) {
> - chomp();
> - if (/^In archive/) {
> - # Archives are always conglomerate
> - $comment = "GCC:GCC:";
> - last;
> - }
> - next if (! /^[ 0-9a-f]{5,} /);
> - $comment .= substr($_, 43);
> - }
> - close($objdumpdata);
> -
> - if (!defined($comment) || $comment !~ /GCC\:.*GCC\:/m) {
> - printf STDERR "No source file found for $fullname\n";
> - }
> - return;
> - }
> - open (my $nmdata, "$nm $basename|")
> - or die "$nm $fullname failed $!\n";
> -
> - my @nmdata;
> - while (<$nmdata>) {
> - chop;
> - ($type, $name) = (split(/ +/, $_, 3))[1..2];
> - # Expected types
> - # A absolute symbol
> - # B weak external reference to data that has been resolved
> - # C global variable, uninitialised
> - # D global variable, initialised
> - # G global variable, initialised, small data section
> - # R global array, initialised
> - # S global variable, uninitialised, small bss
> - # T global label/procedure
> - # U external reference
> - # W weak external reference to text that has been resolved
> - # V similar to W, but the value of the weak symbol becomes zero with no error.
> - # a assembler equate
> - # b static variable, uninitialised
> - # d static variable, initialised
> - # g static variable, initialised, small data section
> - # r static array, initialised
> - # s static variable, uninitialised, small bss
> - # t static label/procedures
> - # w weak external reference to text that has not been resolved
> - # v similar to w
> - # ? undefined type, used a lot by modules
> - if ($type !~ /^[ABCDGRSTUWVabdgrstwv?]$/) {
> - printf STDERR "nm output for $fullname contains unknown type '$_'\n";
> - }
> - elsif ($name =~ /\./) {
> - # name with '.' is local static
> - }
> - else {
> - $type = 'R' if ($type eq '?'); # binutils replaced ? with R at one point
> - # binutils keeps changing the type for exported symbols, force it to R
> - $type = 'R' if ($name =~ /^__ksymtab/ || $name =~ /^__kstrtab/);
> - $name =~ s/_R[a-f0-9]{8}$//; # module versions adds this
> - if ($type =~ /[ABCDGRSTWV]/ &&
> - $name ne 'init_module' &&
> - $name ne 'cleanup_module' &&
> - $name ne 'Using_Versions' &&
> - $name !~ /^Version_[0-9]+$/ &&
> - $name !~ /^__parm_/ &&
> - $name !~ /^__kstrtab/ &&
> - $name !~ /^__ksymtab/ &&
> - $name !~ /^__kcrctab_/ &&
> - $name !~ /^__exitcall_/ &&
> - $name !~ /^__initcall_/ &&
> - $name !~ /^__kdb_initcall_/ &&
> - $name !~ /^__kdb_exitcall_/ &&
> - $name !~ /^__module_/ &&
> - $name !~ /^__mod_/ &&
> - $name !~ /^__crc_/ &&
> - $name ne '__this_module' &&
> - $name ne 'kernel_version') {
> - if (!exists($def{$name})) {
> - $def{$name} = [];
> - }
> - push(@{$def{$name}}, $fullname);
> - }
> - push(@nmdata, "$type $name");
> - if ($name =~ /^__ksymtab_/) {
> - $name = substr($name, 10);
> - if (!exists($ksymtab{$name})) {
> - $ksymtab{$name} = [];
> - }
> - push(@{$ksymtab{$name}}, $fullname);
> - }
> - }
> - }
> - close($nmdata);
> -
> - if ($#nmdata < 0) {
> - printf "No nm data for $fullname\n"
> - unless $nmexception{$fullname};
> - return;
> - }
> - $nmdata{$fullname} = \@nmdata;
> -}
> -
> -sub drop_def
> -{
> - my ($object, $name) = @_;
> - my $nmdata = $nmdata{$object};
> - my ($i, $j);
> - for ($i = 0; $i <= $#{$nmdata}; ++$i) {
> - if ($name eq (split(' ', $nmdata->[$i], 2))[1]) {
> - splice(@{$nmdata{$object}}, $i, 1);
> - my $def = $def{$name};
> - for ($j = 0; $j < $#{$def{$name}}; ++$j) {
> - if ($def{$name}[$j] eq $object) {
> - splice(@{$def{$name}}, $j, 1);
> - }
> - }
> - last;
> - }
> - }
> -}
> -
> -sub list_multiply_defined
> -{
> - foreach my $name (keys(%def)) {
> - if ($#{$def{$name}} > 0) {
> - # Special case for cond_syscall
> - if ($#{$def{$name}} == 1 &&
> - ($name =~ /^sys_/ || $name =~ /^compat_sys_/ ||
> - $name =~ /^sys32_/)) {
> - if($def{$name}[0] eq "kernel/sys_ni.o" ||
> - $def{$name}[1] eq "kernel/sys_ni.o") {
> - &drop_def("kernel/sys_ni.o", $name);
> - next;
> - }
> - }
> -
> - printf "$name is multiply defined in :-\n";
> - foreach my $module (@{$def{$name}}) {
> - printf "\t$module\n";
> - }
> - }
> - }
> -}
> -
> -sub resolve_external_references
> -{
> - my ($kstrtab, $ksymtab, $export);
> -
> - printf "\n";
> - foreach my $object (keys(%nmdata)) {
> - my $nmdata = $nmdata{$object};
> - for (my $i = 0; $i <= $#{$nmdata}; ++$i) {
> - my ($type, $name) = split(' ', $nmdata->[$i], 2);
> - if ($type eq "U" || $type eq "w") {
> - if (exists($def{$name}) || exists($ksymtab{$name})) {
> - # add the owning object to the nmdata
> - $nmdata->[$i] = "$type $name $object";
> - # only count as a reference if it is not EXPORT_...
> - $kstrtab = "R __kstrtab_$name";
> - $ksymtab = "R __ksymtab_$name";
> - $export = 0;
> - for (my $j = 0; $j <= $#{$nmdata}; ++$j) {
> - if ($nmdata->[$j] eq $kstrtab ||
> - $nmdata->[$j] eq $ksymtab) {
> - $export = 1;
> - last;
> - }
> - }
> - if ($export) {
> - $export{$name} = "";
> - }
> - else {
> - $ref{$name} = ""
> - }
> - }
> - elsif ( ! $nameexception{$name}
> - && $name !~ /^__sched_text_/
> - && $name !~ /^__start_/
> - && $name !~ /^__end_/
> - && $name !~ /^__stop_/
> - && $name !~ /^__scheduling_functions_.*_here/
> - && $name !~ /^__.*initcall_/
> - && $name !~ /^__.*per_cpu_start/
> - && $name !~ /^__.*per_cpu_end/
> - && $name !~ /^__alt_instructions/
> - && $name !~ /^__setup_/
> - && $name !~ /^__mod_timer/
> - && $name !~ /^__mod_page_state/
> - && $name !~ /^init_module/
> - && $name !~ /^cleanup_module/
> - ) {
> - printf "Cannot resolve ";
> - printf "weak " if ($type eq "w");
> - printf "reference to $name from $object\n";
> - }
> - }
> - }
> - }
> -}
> -
> -sub list_extra_externals
> -{
> - my %noref = ();
> -
> - foreach my $name (keys(%def)) {
> - if (! exists($ref{$name})) {
> - my @module = @{$def{$name}};
> - foreach my $module (@module) {
> - if (! exists($noref{$module})) {
> - $noref{$module} = [];
> - }
> - push(@{$noref{$module}}, $name);
> - }
> - }
> - }
> - if (%noref) {
> - printf "\nExternally defined symbols with no external references\n";
> - foreach my $module (sort(keys(%noref))) {
> - printf " $module\n";
> - foreach (sort(@{$noref{$module}})) {
> - my $export;
> - if (exists($export{$_})) {
> - $export = " (export only)";
> - } else {
> - $export = "";
> - }
> - printf " $_$export\n";
> - }
> - }
> - }
> -}
>
> base-commit: 3fdd47c3b40ac48e6e6e5904cf24d12e6e073a96
> --
> 2.28.0.497.g54e85e7af1ac
>

--
Best Regards
Masahiro Yamada

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