ANDROID: Add missing CFI jump table symbols to kallsyms
With CONFIG_LTO_CLANG_FULL, LLVM drops all CFI jump table symbols from vmlinux, which doesn't affect kernel functionality, but can make stack traces and other kernel output that prints out jump table addresses harder to read. This change works around the issue for now by adding a script that tells kallsyms about the missing jump table symbols, even though they don't actually exist in the symbol table, and generates a linker script to add the missing symbols to kernel modules. Bug: 186152035 Bug: 187415564 Change-Id: Ic3c51751c756f2f5fb2a31229e16c3397eb6e666 Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
This commit is contained in:
Sami Tolvanen
Todd Kjos
parent
a1fbf0ead8
commit
27eb5ffcb7
@ -4254,6 +4254,11 @@ static inline int is_arm_mapping_symbol(const char *str)
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&& (str[2] == '\0' || str[2] == '.');
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}
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static inline int is_cfi_typeid_symbol(const char *str)
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{
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return !strncmp(str, "__typeid__", 10);
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}
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static const char *kallsyms_symbol_name(struct mod_kallsyms *kallsyms, unsigned int symnum)
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{
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return kallsyms->strtab + kallsyms->symtab[symnum].st_name;
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@ -4292,7 +4297,8 @@ static const char *find_kallsyms_symbol(struct module *mod,
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/* We ignore unnamed symbols: they're uninformative
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* and inserted at a whim. */
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if (*kallsyms_symbol_name(kallsyms, i) == '\0'
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|| is_arm_mapping_symbol(kallsyms_symbol_name(kallsyms, i)))
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|| is_arm_mapping_symbol(kallsyms_symbol_name(kallsyms, i))
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|| is_cfi_typeid_symbol(kallsyms_symbol_name(kallsyms, i)))
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continue;
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if (thisval <= addr && thisval > bestval) {
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@ -58,6 +58,23 @@ quiet_cmd_ld_ko_o = LD [M] $@
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-T scripts/module.lds -o $@ $(filter %.o, $^); \
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$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)
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ifdef CONFIG_CFI_CLANG
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# LLVM can drops jump table symbols from the final binary. Add them
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# back to make stack traces and other symbol output readable.
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cmd_ld_ko_o += ; \
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$(srctree)/scripts/generate_cfi_kallsyms.pl --module \
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$@ > $(@:.ko=.lds); \
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if [ -s $(@:.ko=.lds) ]; then \
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$(LD) -r $(KBUILD_LDFLAGS) \
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$(KBUILD_LDFLAGS_MODULE) $(LDFLAGS_MODULE) \
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-T $(@:.ko=.lds) \
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-o $(@:.ko=.tmp.ko) $@; \
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mv -f $(@:.ko=.tmp.ko) $@; \
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else \
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rm -f $(@:.ko=.lds); \
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fi
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endif
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$(modules): %.ko: %$(prelink-ext).o %.mod.o scripts/module.lds FORCE
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+$(call if_changed,ld_ko_o)
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308
scripts/generate_cfi_kallsyms.pl
Executable file
308
scripts/generate_cfi_kallsyms.pl
Executable file
@ -0,0 +1,308 @@
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#!/usr/bin/env perl
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# SPDX-License-Identifier: GPL-2.0
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#
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# Generates a list of Control-Flow Integrity (CFI) jump table symbols
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# for kallsyms.
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#
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# Copyright (C) 2021 Google LLC
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use strict;
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use warnings;
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## parameters
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my $ismodule = 0;
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my $file;
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foreach (@ARGV) {
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if ($_ eq '--module') {
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$ismodule = 1;
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} elsif (!defined($file)) {
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$file = $_;
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} else {
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die "$0: usage $0 [--module] binary";
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}
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}
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## environment
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my $readelf = $ENV{'READELF'} || die "$0: ERROR: READELF not set?";
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my $objdump = $ENV{'OBJDUMP'} || die "$0: ERROR: OBJDUMP not set?";
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my $nm = $ENV{'NM'} || die "$0: ERROR: NM not set?";
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## jump table addresses
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my $cfi_jt = {};
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## text symbols
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my $text_symbols = {};
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## parser state
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use constant {
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UNKNOWN => 0,
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SYMBOL => 1,
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HINT => 2,
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BRANCH => 3,
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RELOC => 4
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};
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## trims leading zeros from a string
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sub trim_zeros {
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my ($n) = @_;
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$n =~ s/^0+//;
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$n = 0 if ($n eq '');
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return $n;
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}
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## finds __cfi_jt_* symbols from the binary to locate the start and end of the
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## jump table
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sub find_cfi_jt {
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open(my $fh, "\"$readelf\" --symbols \"$file\" 2>/dev/null | grep __cfi_jt_ |")
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or die "$0: ERROR: failed to execute \"$readelf\": $!";
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while (<$fh>) {
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chomp;
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my ($addr, $name) = $_ =~ /\:.*([a-f0-9]{16}).*\s__cfi_jt_(.*)/;
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if (defined($addr) && defined($name)) {
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$cfi_jt->{$name} = $addr;
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}
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}
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close($fh);
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die "$0: ERROR: __cfi_jt_start symbol missing" if !exists($cfi_jt->{"start"});
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die "$0: ERROR: __cfi_jt_end symbol missing" if !exists($cfi_jt->{"end"});
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}
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my $last = UNKNOWN;
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my $last_symbol;
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my $last_hint_addr;
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my $last_branch_addr;
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my $last_branch_target;
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my $last_reloc_target;
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sub is_symbol {
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my ($line) = @_;
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my ($addr, $symbol) = $_ =~ /^([a-f0-9]{16})\s<([^>]+)>\:/;
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if (defined($addr) && defined($symbol)) {
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$last = SYMBOL;
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$last_symbol = $symbol;
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return 1;
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}
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return 0;
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}
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sub is_hint {
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my ($line) = @_;
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my ($hint) = $_ =~ /^\s*([a-f0-9]+)\:.*\s+hint\s+#/;
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if (defined($hint)) {
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$last = HINT;
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$last_hint_addr = $hint;
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return 1;
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}
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return 0;
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}
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sub find_text_symbol {
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my ($target) = @_;
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my ($symbol, $expr, $offset) = $target =~ /^(\S*)([-\+])0x([a-f0-9]+)?$/;
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if (!defined($symbol) || !defined(!$expr) || !defined($offset)) {
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return $target;
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}
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if ($symbol =~ /^\.((init|exit)\.)?text$/ && $expr eq '+') {
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$offset = trim_zeros($offset);
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my $actual = $text_symbols->{"$symbol+$offset"};
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if (!defined($actual)) {
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die "$0: unknown symbol at $symbol+0x$offset";
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}
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$symbol = $actual;
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}
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return $symbol;
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}
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sub is_branch {
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my ($line) = @_;
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my ($addr, $instr, $branch_target) = $_ =~
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/^\s*([a-f0-9]+)\:.*(b|jmpq?)\s+0x[a-f0-9]+\s+<([^>]+)>/;
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if (defined($addr) && defined($instr) && defined($branch_target)) {
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if ($last eq HINT) {
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$last_branch_addr = $last_hint_addr;
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} else {
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$last_branch_addr = $addr;
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}
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$last = BRANCH;
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$last_branch_target = find_text_symbol($branch_target);
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return 1;
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}
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return 0;
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}
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sub is_branch_reloc {
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my ($line) = @_;
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if ($last ne BRANCH) {
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return 0;
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}
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my ($addr, $type, $reloc_target) = /\s*([a-f0-9]{16})\:\s+R_(\S+)\s+(\S+)$/;
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if (defined($addr) && defined($type) && defined($reloc_target)) {
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$last = RELOC;
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$last_reloc_target = find_text_symbol($reloc_target);
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return 1;
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}
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return 0;
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}
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## walks through the jump table looking for branches and prints out a jump
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## table symbol for each branch if one is missing
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sub print_missing_symbols {
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my @symbols;
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open(my $fh, "\"$objdump\" -d -r " .
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"--start-address=0x" . $cfi_jt->{"start"} .
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" --stop-address=0x" . $cfi_jt->{"end"} .
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" \"$file\" 2>/dev/null |")
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or die "$0: ERROR: failed to execute \"$objdump\": $!";
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while (<$fh>) {
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chomp;
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if (is_symbol($_) || is_hint($_)) {
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next;
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}
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my $cfi_jt_symbol;
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if (is_branch($_)) {
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if ($ismodule) {
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next; # wait for the relocation
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}
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$cfi_jt_symbol = $last_branch_target;
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} elsif (is_branch_reloc($_)) {
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$cfi_jt_symbol = $last_reloc_target;
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} else {
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next;
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}
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# ignore functions with a canonical jump table
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if ($cfi_jt_symbol =~ /\.cfi$/) {
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next;
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}
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$cfi_jt_symbol .= ".cfi_jt";
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$cfi_jt->{$last_branch_addr} = $cfi_jt_symbol;
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if (defined($last_symbol) && $last_symbol eq $cfi_jt_symbol) {
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next; # already exists
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}
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# print out the symbol
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if ($ismodule) {
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push(@symbols, "\t\t$cfi_jt_symbol = . + 0x$last_branch_addr;");
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} else {
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push(@symbols, "$last_branch_addr t $cfi_jt_symbol");
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}
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}
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close($fh);
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if (!scalar(@symbols)) {
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return;
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}
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if ($ismodule) {
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print "SECTIONS {\n";
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# With -fpatchable-function-entry, LLD isn't happy without this
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print "\t__patchable_function_entries : { *(__patchable_function_entries) }\n";
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print "\t.text : {\n";
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}
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foreach (@symbols) {
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print "$_\n";
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}
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if ($ismodule) {
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print "\t}\n}\n";
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}
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}
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## reads defined text symbols from the file
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sub read_symbols {
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open(my $fh, "\"$objdump\" --syms \"$file\" 2>/dev/null |")
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or die "$0: ERROR: failed to execute \"$nm\": $!";
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while (<$fh>) {
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chomp;
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# llvm/tools/llvm-objdump/objdump.cpp:objdump::printSymbol
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my ($addr, $debug, $section, $ref, $symbol) = $_ =~
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/^([a-f0-9]{16})\s.{5}(.).{2}(\S+)\s[a-f0-9]{16}(\s\.\S+)?\s(.*)$/;
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if (defined($addr) && defined($section) && defined($symbol)) {
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if (!($section =~ /^\.((init|exit)\.)?text$/)) {
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next;
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}
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# skip arm mapping symbols
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if ($symbol =~ /^\$[xd]\.\d+$/) {
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next;
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}
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if (defined($debug) && $debug eq "d") {
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next;
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}
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$addr = trim_zeros($addr);
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$text_symbols->{"$section+$addr"} = $symbol;
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}
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}
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close($fh);
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}
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## prints out the remaining symbols from nm -n, filtering out the unnecessary
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## __typeid__ symbols aliasing the jump table symbols we added
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sub print_kallsyms {
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open(my $fh, "\"$nm\" -n \"$file\" 2>/dev/null |")
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or die "$0: ERROR: failed to execute \"$nm\": $!";
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while (<$fh>) {
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chomp;
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my ($addr, $symbol) = $_ =~ /^([a-f0-9]{16})\s.\s(.*)$/;
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if (defined($addr) && defined($symbol)) {
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# drop duplicate __typeid__ symbols
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if ($symbol =~ /^__typeid__.*_global_addr$/ &&
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exists($cfi_jt->{$addr})) {
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next;
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}
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}
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print "$_\n";
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}
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close($fh);
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}
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## main
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find_cfi_jt();
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if ($ismodule) {
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read_symbols();
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print_missing_symbols();
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} else {
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print_missing_symbols();
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print_kallsyms();
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}
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@ -260,7 +260,15 @@ kallsyms()
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fi
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info KSYMS ${2}
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${NM} -n ${1} | scripts/kallsyms ${kallsymopt} > ${2}
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if [ -n "${CONFIG_CFI_CLANG}" ]; then
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${PERL} ${srctree}/scripts/generate_cfi_kallsyms.pl ${1} | \
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sort -n > .tmp_kallsyms
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else
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${NM} -n ${1} > .tmp_kallsyms
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fi
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scripts/kallsyms ${kallsymopt} < .tmp_kallsyms > ${2}
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}
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# Perform one step in kallsyms generation, including temporary linking of
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@ -298,6 +306,7 @@ cleanup()
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{
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rm -f .btf.*
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rm -f .tmp_System.map
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rm -f .tmp_kallsyms
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rm -f .tmp_initcalls.lds
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rm -f .tmp_symversions.lds
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rm -f .tmp_vmlinux*
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@ -60,7 +60,10 @@ SECTIONS {
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*/
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.text : ALIGN(PAGE_SIZE) {
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*(.text.__cfi_check)
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*(.text .text.[0-9a-zA-Z_]* .text..L.cfi*)
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*(.text .text.[0-9a-zA-Z_]*)
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__cfi_jt_start = .;
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*(.text..L.cfi.jumptable .text..L.cfi.jumptable.*)
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__cfi_jt_end = .;
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}
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#endif
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}
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