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https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-08-23 09:19:51 +00:00
![Ard Biesheuvel](/assets/img/avatar_default.png)
Similar to how relative extables are implemented, it is possible to emit the kallsyms table in such a way that it contains offsets relative to some anchor point in the kernel image rather than absolute addresses. On 64-bit architectures, it cuts the size of the kallsyms address table in half, since offsets between kernel symbols can typically be expressed in 32 bits. This saves several hundreds of kilobytes of permanent .rodata on average. In addition, the kallsyms address table is no longer subject to dynamic relocation when CONFIG_RELOCATABLE is in effect, so the relocation work done after decompression now doesn't have to do relocation updates for all these values. This saves up to 24 bytes (i.e., the size of a ELF64 RELA relocation table entry) per value, which easily adds up to a couple of megabytes of uncompressed __init data on ppc64 or arm64. Even if these relocation entries typically compress well, the combined size reduction of 2.8 MB uncompressed for a ppc64_defconfig build (of which 2.4 MB is __init data) results in a ~500 KB space saving in the compressed image. Since it is useful for some architectures (like x86) to retain the ability to emit absolute values as well, this patch also adds support for capturing both absolute and relative values when KALLSYMS_ABSOLUTE_PERCPU is in effect, by emitting absolute per-cpu addresses as positive 32-bit values, and addresses relative to the lowest encountered relative symbol as negative values, which are subtracted from the runtime address of this base symbol to produce the actual address. Support for the above is enabled by default for all architectures except IA-64 and Tile-GX, whose symbols are too far apart to capture in this manner. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Tested-by: Guenter Roeck <linux@roeck-us.net> Reviewed-by: Kees Cook <keescook@chromium.org> Tested-by: Kees Cook <keescook@chromium.org> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Ingo Molnar <mingo@kernel.org> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Michal Marek <mmarek@suse.cz> Cc: Rusty Russell <rusty@rustcorp.com.au> Cc: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
472 lines
13 KiB
Prolog
Executable file
472 lines
13 KiB
Prolog
Executable file
#!/usr/bin/perl -w
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#
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# namespace.pl. Mon Aug 30 2004
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#
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# Perform a name space analysis on the linux kernel.
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#
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# Copyright Keith Owens <kaos@ocs.com.au>. GPL.
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#
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# Invoke by changing directory to the top of the kernel object
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# tree then namespace.pl, no parameters.
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#
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# Tuned for 2.1.x kernels with the new module handling, it will
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# work with 2.0 kernels as well.
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#
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# Last change 2.6.9-rc1, adding support for separate source and object
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# trees.
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#
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# The source must be compiled/assembled first, the object files
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# are the primary input to this script. Incomplete or missing
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# objects will result in a flawed analysis. Compile both vmlinux
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# and modules.
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#
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# Even with complete objects, treat the result of the analysis
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# with caution. Some external references are only used by
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# certain architectures, others with certain combinations of
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# configuration parameters. Ideally the source should include
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# something like
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#
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# #ifndef CONFIG_...
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# static
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# #endif
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# symbol_definition;
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#
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# so the symbols are defined as static unless a particular
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# CONFIG_... requires it to be external.
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#
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# A symbol that is suffixed with '(export only)' has these properties
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#
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# * It is global.
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# * It is marked EXPORT_SYMBOL or EXPORT_SYMBOL_GPL, either in the same
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# source file or a different source file.
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# * Given the current .config, nothing uses the symbol.
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#
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# The symbol is a candidate for conversion to static, plus removal of the
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# export. But be careful that a different .config might use the symbol.
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#
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#
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# Name space analysis and cleanup is an iterative process. You cannot
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# expect to find all the problems in a single pass.
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#
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# * Identify possibly unnecessary global declarations, verify that they
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# really are unnecessary and change them to static.
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# * Compile and fix up gcc warnings about static, removing dead symbols
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# as necessary.
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# * make clean and rebuild with different configs (especially
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# CONFIG_MODULES=n) to see which symbols are being defined when the
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# config does not require them. These symbols bloat the kernel object
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# for no good reason, which is frustrating for embedded systems.
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# * Wrap config sensitive symbols in #ifdef CONFIG_foo, as long as the
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# code does not get too ugly.
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# * Repeat the name space analysis until you can live with with the
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# result.
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#
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require 5; # at least perl 5
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use strict;
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use File::Find;
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my $nm = ($ENV{'NM'} || "nm") . " -p";
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my $objdump = ($ENV{'OBJDUMP'} || "objdump") . " -s -j .comment";
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my $srctree = "";
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my $objtree = "";
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$srctree = "$ENV{'srctree'}/" if (exists($ENV{'srctree'}));
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$objtree = "$ENV{'objtree'}/" if (exists($ENV{'objtree'}));
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if ($#ARGV != -1) {
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print STDERR "usage: $0 takes no parameters\n";
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die("giving up\n");
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}
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my %nmdata = (); # nm data for each object
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my %def = (); # all definitions for each name
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my %ksymtab = (); # names that appear in __ksymtab_
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my %ref = (); # $ref{$name} exists if there is a true external reference to $name
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my %export = (); # $export{$name} exists if there is an EXPORT_... of $name
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my %nmexception = (
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'fs/ext3/bitmap' => 1,
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'fs/ext4/bitmap' => 1,
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'arch/x86/lib/thunk_32' => 1,
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'arch/x86/lib/cmpxchg' => 1,
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'arch/x86/vdso/vdso32/note' => 1,
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'lib/irq_regs' => 1,
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'usr/initramfs_data' => 1,
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'drivers/scsi/aic94xx/aic94xx_dump' => 1,
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'drivers/scsi/libsas/sas_dump' => 1,
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'lib/dec_and_lock' => 1,
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'drivers/ide/ide-probe-mini' => 1,
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'usr/initramfs_data' => 1,
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'drivers/acpi/acpia/exdump' => 1,
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'drivers/acpi/acpia/rsdump' => 1,
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'drivers/acpi/acpia/nsdumpdv' => 1,
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'drivers/acpi/acpia/nsdump' => 1,
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'arch/ia64/sn/kernel/sn2/io' => 1,
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'arch/ia64/kernel/gate-data' => 1,
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'security/capability' => 1,
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'fs/ntfs/sysctl' => 1,
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'fs/jfs/jfs_debug' => 1,
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);
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my %nameexception = (
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'mod_use_count_' => 1,
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'__initramfs_end' => 1,
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'__initramfs_start' => 1,
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'_einittext' => 1,
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'_sinittext' => 1,
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'kallsyms_names' => 1,
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'kallsyms_num_syms' => 1,
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'kallsyms_addresses'=> 1,
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'kallsyms_offsets' => 1,
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'kallsyms_relative_base'=> 1,
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'__this_module' => 1,
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'_etext' => 1,
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'_edata' => 1,
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'_end' => 1,
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'__bss_start' => 1,
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'_text' => 1,
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'_stext' => 1,
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'__gp' => 1,
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'ia64_unw_start' => 1,
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'ia64_unw_end' => 1,
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'__init_begin' => 1,
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'__init_end' => 1,
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'__bss_stop' => 1,
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'__nosave_begin' => 1,
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'__nosave_end' => 1,
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'pg0' => 1,
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'vdso_enabled' => 1,
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'__stack_chk_fail' => 1,
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'VDSO32_PRELINK' => 1,
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'VDSO32_vsyscall' => 1,
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'VDSO32_rt_sigreturn'=>1,
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'VDSO32_sigreturn' => 1,
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);
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&find(\&linux_objects, '.'); # find the objects and do_nm on them
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&list_multiply_defined();
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&resolve_external_references();
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&list_extra_externals();
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exit(0);
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sub linux_objects
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{
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# Select objects, ignoring objects which are only created by
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# merging other objects. Also ignore all of modules, scripts
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# and compressed. Most conglomerate objects are handled by do_nm,
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# this list only contains the special cases. These include objects
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# that are linked from just one other object and objects for which
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# there is really no permanent source file.
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my $basename = $_;
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$_ = $File::Find::name;
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s:^\./::;
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if (/.*\.o$/ &&
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! (
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m:/built-in.o$:
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|| m:arch/x86/vdso/:
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|| m:arch/x86/boot/:
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|| m:arch/ia64/ia32/ia32.o$:
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|| m:arch/ia64/kernel/gate-syms.o$:
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|| m:arch/ia64/lib/__divdi3.o$:
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|| m:arch/ia64/lib/__divsi3.o$:
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|| m:arch/ia64/lib/__moddi3.o$:
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|| m:arch/ia64/lib/__modsi3.o$:
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|| m:arch/ia64/lib/__udivdi3.o$:
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|| m:arch/ia64/lib/__udivsi3.o$:
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|| m:arch/ia64/lib/__umoddi3.o$:
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|| m:arch/ia64/lib/__umodsi3.o$:
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|| m:arch/ia64/scripts/check_gas_for_hint.o$:
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|| m:arch/ia64/sn/kernel/xp.o$:
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|| m:boot/bbootsect.o$:
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|| m:boot/bsetup.o$:
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|| m:/bootsect.o$:
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|| m:/boot/setup.o$:
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|| m:/compressed/:
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|| m:drivers/cdrom/driver.o$:
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|| m:drivers/char/drm/tdfx_drv.o$:
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|| m:drivers/ide/ide-detect.o$:
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|| m:drivers/ide/pci/idedriver-pci.o$:
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|| m:drivers/media/media.o$:
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|| m:drivers/scsi/sd_mod.o$:
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|| m:drivers/video/video.o$:
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|| m:fs/devpts/devpts.o$:
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|| m:fs/exportfs/exportfs.o$:
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|| m:fs/hugetlbfs/hugetlbfs.o$:
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|| m:fs/msdos/msdos.o$:
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|| m:fs/nls/nls.o$:
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|| m:fs/ramfs/ramfs.o$:
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|| m:fs/romfs/romfs.o$:
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|| m:fs/vfat/vfat.o$:
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|| m:init/mounts.o$:
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|| m:^modules/:
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|| m:net/netlink/netlink.o$:
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|| m:net/sched/sched.o$:
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|| m:/piggy.o$:
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|| m:^scripts/:
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|| m:sound/.*/snd-:
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|| m:^.*/\.tmp_:
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|| m:^\.tmp_:
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|| m:/vmlinux-obj.o$:
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|| m:^tools/:
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)
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) {
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do_nm($basename, $_);
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}
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$_ = $basename; # File::Find expects $_ untouched (undocumented)
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}
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sub do_nm
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{
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my ($basename, $fullname) = @_;
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my ($source, $type, $name);
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if (! -e $basename) {
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printf STDERR "$basename does not exist\n";
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return;
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}
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if ($fullname !~ /\.o$/) {
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printf STDERR "$fullname is not an object file\n";
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return;
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}
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($source = $basename) =~ s/\.o$//;
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if (-e "$source.c" || -e "$source.S") {
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$source = "$objtree$File::Find::dir/$source";
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} else {
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$source = "$srctree$File::Find::dir/$source";
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}
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if (! -e "$source.c" && ! -e "$source.S") {
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# No obvious source, exclude the object if it is conglomerate
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open(my $objdumpdata, "$objdump $basename|")
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or die "$objdump $fullname failed $!\n";
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my $comment;
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while (<$objdumpdata>) {
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chomp();
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if (/^In archive/) {
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# Archives are always conglomerate
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$comment = "GCC:GCC:";
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last;
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}
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next if (! /^[ 0-9a-f]{5,} /);
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$comment .= substr($_, 43);
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}
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close($objdumpdata);
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if (!defined($comment) || $comment !~ /GCC\:.*GCC\:/m) {
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printf STDERR "No source file found for $fullname\n";
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}
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return;
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}
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open (my $nmdata, "$nm $basename|")
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or die "$nm $fullname failed $!\n";
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my @nmdata;
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while (<$nmdata>) {
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chop;
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($type, $name) = (split(/ +/, $_, 3))[1..2];
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# Expected types
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# A absolute symbol
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# B weak external reference to data that has been resolved
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# C global variable, uninitialised
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# D global variable, initialised
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# G global variable, initialised, small data section
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# R global array, initialised
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# S global variable, uninitialised, small bss
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# T global label/procedure
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# U external reference
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# W weak external reference to text that has been resolved
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# V similar to W, but the value of the weak symbol becomes zero with no error.
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# a assembler equate
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# b static variable, uninitialised
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# d static variable, initialised
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# g static variable, initialised, small data section
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# r static array, initialised
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# s static variable, uninitialised, small bss
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# t static label/procedures
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# w weak external reference to text that has not been resolved
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# v similar to w
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# ? undefined type, used a lot by modules
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if ($type !~ /^[ABCDGRSTUWVabdgrstwv?]$/) {
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printf STDERR "nm output for $fullname contains unknown type '$_'\n";
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}
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elsif ($name =~ /\./) {
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# name with '.' is local static
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}
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else {
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$type = 'R' if ($type eq '?'); # binutils replaced ? with R at one point
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# binutils keeps changing the type for exported symbols, force it to R
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$type = 'R' if ($name =~ /^__ksymtab/ || $name =~ /^__kstrtab/);
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$name =~ s/_R[a-f0-9]{8}$//; # module versions adds this
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if ($type =~ /[ABCDGRSTWV]/ &&
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$name ne 'init_module' &&
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$name ne 'cleanup_module' &&
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$name ne 'Using_Versions' &&
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$name !~ /^Version_[0-9]+$/ &&
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$name !~ /^__parm_/ &&
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$name !~ /^__kstrtab/ &&
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$name !~ /^__ksymtab/ &&
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$name !~ /^__kcrctab_/ &&
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$name !~ /^__exitcall_/ &&
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$name !~ /^__initcall_/ &&
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$name !~ /^__kdb_initcall_/ &&
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$name !~ /^__kdb_exitcall_/ &&
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$name !~ /^__module_/ &&
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$name !~ /^__mod_/ &&
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$name !~ /^__crc_/ &&
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$name ne '__this_module' &&
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$name ne 'kernel_version') {
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if (!exists($def{$name})) {
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$def{$name} = [];
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}
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push(@{$def{$name}}, $fullname);
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}
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push(@nmdata, "$type $name");
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if ($name =~ /^__ksymtab_/) {
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$name = substr($name, 10);
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if (!exists($ksymtab{$name})) {
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$ksymtab{$name} = [];
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}
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push(@{$ksymtab{$name}}, $fullname);
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}
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}
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}
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close($nmdata);
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if ($#nmdata < 0) {
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printf "No nm data for $fullname\n"
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unless $nmexception{$fullname};
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return;
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}
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$nmdata{$fullname} = \@nmdata;
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}
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sub drop_def
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{
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my ($object, $name) = @_;
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my $nmdata = $nmdata{$object};
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my ($i, $j);
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for ($i = 0; $i <= $#{$nmdata}; ++$i) {
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if ($name eq (split(' ', $nmdata->[$i], 2))[1]) {
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splice(@{$nmdata{$object}}, $i, 1);
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my $def = $def{$name};
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for ($j = 0; $j < $#{$def{$name}}; ++$j) {
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if ($def{$name}[$j] eq $object) {
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splice(@{$def{$name}}, $j, 1);
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}
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}
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last;
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}
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}
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}
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sub list_multiply_defined
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{
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foreach my $name (keys(%def)) {
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if ($#{$def{$name}} > 0) {
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# Special case for cond_syscall
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if ($#{$def{$name}} == 1 &&
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($name =~ /^sys_/ || $name =~ /^compat_sys_/ ||
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$name =~ /^sys32_/)) {
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if($def{$name}[0] eq "kernel/sys_ni.o" ||
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$def{$name}[1] eq "kernel/sys_ni.o") {
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&drop_def("kernel/sys_ni.o", $name);
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next;
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}
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}
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printf "$name is multiply defined in :-\n";
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foreach my $module (@{$def{$name}}) {
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printf "\t$module\n";
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}
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}
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}
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}
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sub resolve_external_references
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{
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my ($kstrtab, $ksymtab, $export);
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printf "\n";
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foreach my $object (keys(%nmdata)) {
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my $nmdata = $nmdata{$object};
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for (my $i = 0; $i <= $#{$nmdata}; ++$i) {
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my ($type, $name) = split(' ', $nmdata->[$i], 2);
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if ($type eq "U" || $type eq "w") {
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if (exists($def{$name}) || exists($ksymtab{$name})) {
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# add the owning object to the nmdata
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$nmdata->[$i] = "$type $name $object";
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# only count as a reference if it is not EXPORT_...
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$kstrtab = "R __kstrtab_$name";
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$ksymtab = "R __ksymtab_$name";
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$export = 0;
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for (my $j = 0; $j <= $#{$nmdata}; ++$j) {
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if ($nmdata->[$j] eq $kstrtab ||
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$nmdata->[$j] eq $ksymtab) {
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$export = 1;
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last;
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}
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}
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if ($export) {
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$export{$name} = "";
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}
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else {
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$ref{$name} = ""
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}
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}
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elsif ( ! $nameexception{$name}
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&& $name !~ /^__sched_text_/
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&& $name !~ /^__start_/
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&& $name !~ /^__end_/
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&& $name !~ /^__stop_/
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&& $name !~ /^__scheduling_functions_.*_here/
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&& $name !~ /^__.*initcall_/
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&& $name !~ /^__.*per_cpu_start/
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&& $name !~ /^__.*per_cpu_end/
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&& $name !~ /^__alt_instructions/
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&& $name !~ /^__setup_/
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&& $name !~ /^__mod_timer/
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|
&& $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";
|
|
}
|
|
}
|
|
}
|
|
}
|