elf_update_symbol fails to preserve the special st_shndx values
between [SHN_LORESERVE, SHN_HIRESERVE], which results in it
converting SHN_ABS entries into SHN_UNDEF, for example. Explicitly
check for the special indexes and ensure these symbols are not
marked undefined.
Fixes: ead165fa10 ("objtool: Fix symbol creation")
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220908215504.3686827-17-samitolvanen@google.com
Commit c087c6e7b5 ("objtool: Fix type of reloc::addend") failed to
appreciate cross building from ILP32 hosts, where 'int' == 'long' and
the issue persists.
As such, use s64/int64_t/Elf64_Sxword for this field and suffer the
pain that is ISO C99 printf formats for it.
Fixes: c087c6e7b5 ("objtool: Fix type of reloc::addend")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
[peterz: reword changelog, s/long long/s64/]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/alpine.LRH.2.02.2205161041260.11556@file01.intranet.prod.int.rdu2.redhat.com
Nathan reported objtool failing with the following messages:
warning: objtool: no non-local symbols !?
warning: objtool: gelf_update_symshndx: invalid section index
The problem is due to commit 4abff6d48d ("objtool: Fix code relocs
vs weak symbols") failing to consider the case where an object would
have no non-local symbols.
The problem that commit tries to address is adding a STB_LOCAL symbol
to the symbol table in light of the ELF spec's requirement that:
In each symbol table, all symbols with STB_LOCAL binding preced the
weak and global symbols. As ``Sections'' above describes, a symbol
table section's sh_info section header member holds the symbol table
index for the first non-local symbol.
The approach taken is to find this first non-local symbol, move that
to the end and then re-use the freed spot to insert a new local symbol
and increment sh_info.
Except it never considered the case of object files without global
symbols and got a whole bunch of details wrong -- so many in fact that
it is a wonder it ever worked :/
Specifically:
- It failed to re-hash the symbol on the new index, so a subsequent
find_symbol_by_index() would not find it at the new location and a
query for the old location would now return a non-deterministic
choice between the old and new symbol.
- It failed to appreciate that the GElf wrappers are not a valid disk
format (it works because GElf is basically Elf64 and we only
support x86_64 atm.)
- It failed to fully appreciate how horrible the libelf API really is
and got the gelf_update_symshndx() call pretty much completely
wrong; with the direct consequence that if inserting a second
STB_LOCAL symbol would require moving the same STB_GLOBAL symbol
again it would completely come unstuck.
Write a new elf_update_symbol() function that wraps all the magic
required to update or create a new symbol at a given index.
Specifically, gelf_update_sym*() require an @ndx argument that is
relative to the @data argument; this means you have to manually
iterate the section data descriptor list and update @ndx.
Fixes: 4abff6d48d ("objtool: Fix code relocs vs weak symbols")
Reported-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Cc: <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/YoPCTEYjoPqE4ZxB@hirez.programming.kicks-ass.net
The '--lto' option is a confusing way of telling objtool to do stack
validation despite it being a linked object. It's no longer needed now
that an explicit '--stackval' option exists. The '--vmlinux' option is
also redundant.
Remove both options in favor of a straightforward '--link' option which
identifies a linked object.
Also, implicitly set '--link' with a warning if the user forgets to do
so and we can tell that it's a linked object. This makes it easier for
manual vmlinux runs.
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Link: https://lkml.kernel.org/r/dcd3ceffd15a54822c6183e5766d21ad06082b45.1650300597.git.jpoimboe@redhat.com
Split the existing options into two groups: actions, which actually do
something; and options, which modify the actions in some way.
Also there's no need to have short flags for all the non-action options.
Reserve short flags for the more important actions.
While at it:
- change a few of the short flags to be more intuitive
- make option descriptions more consistently descriptive
- sort options in the source like they are when printed
- move options to a global struct
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Link: https://lkml.kernel.org/r/9dcaa752f83aca24b1b21f0b0eeb28a0c181c0b0.1650300597.git.jpoimboe@redhat.com
Occasionally objtool driven code patching (think .static_call_sites
.retpoline_sites etc..) goes sideways and it tries to patch an
instruction that doesn't match.
Much head-scatching and cursing later the problem is as outlined below
and affects every section that objtool generates for us, very much
including the ORC data. The below uses .static_call_sites because it's
convenient for demonstration purposes, but as mentioned the ORC
sections, .retpoline_sites and __mount_loc are all similarly affected.
Consider:
foo-weak.c:
extern void __SCT__foo(void);
__attribute__((weak)) void foo(void)
{
return __SCT__foo();
}
foo.c:
extern void __SCT__foo(void);
extern void my_foo(void);
void foo(void)
{
my_foo();
return __SCT__foo();
}
These generate the obvious code
(gcc -O2 -fcf-protection=none -fno-asynchronous-unwind-tables -c foo*.c):
foo-weak.o:
0000000000000000 <foo>:
0: e9 00 00 00 00 jmpq 5 <foo+0x5> 1: R_X86_64_PLT32 __SCT__foo-0x4
foo.o:
0000000000000000 <foo>:
0: 48 83 ec 08 sub $0x8,%rsp
4: e8 00 00 00 00 callq 9 <foo+0x9> 5: R_X86_64_PLT32 my_foo-0x4
9: 48 83 c4 08 add $0x8,%rsp
d: e9 00 00 00 00 jmpq 12 <foo+0x12> e: R_X86_64_PLT32 __SCT__foo-0x4
Now, when we link these two files together, you get something like
(ld -r -o foos.o foo-weak.o foo.o):
foos.o:
0000000000000000 <foo-0x10>:
0: e9 00 00 00 00 jmpq 5 <foo-0xb> 1: R_X86_64_PLT32 __SCT__foo-0x4
5: 66 2e 0f 1f 84 00 00 00 00 00 nopw %cs:0x0(%rax,%rax,1)
f: 90 nop
0000000000000010 <foo>:
10: 48 83 ec 08 sub $0x8,%rsp
14: e8 00 00 00 00 callq 19 <foo+0x9> 15: R_X86_64_PLT32 my_foo-0x4
19: 48 83 c4 08 add $0x8,%rsp
1d: e9 00 00 00 00 jmpq 22 <foo+0x12> 1e: R_X86_64_PLT32 __SCT__foo-0x4
Noting that ld preserves the weak function text, but strips the symbol
off of it (hence objdump doing that funny negative offset thing). This
does lead to 'interesting' unused code issues with objtool when ran on
linked objects, but that seems to be working (fingers crossed).
So far so good.. Now lets consider the objtool static_call output
section (readelf output, old binutils):
foo-weak.o:
Relocation section '.rela.static_call_sites' at offset 0x2c8 contains 1 entry:
Offset Info Type Symbol's Value Symbol's Name + Addend
0000000000000000 0000000200000002 R_X86_64_PC32 0000000000000000 .text + 0
0000000000000004 0000000d00000002 R_X86_64_PC32 0000000000000000 __SCT__foo + 1
foo.o:
Relocation section '.rela.static_call_sites' at offset 0x310 contains 2 entries:
Offset Info Type Symbol's Value Symbol's Name + Addend
0000000000000000 0000000200000002 R_X86_64_PC32 0000000000000000 .text + d
0000000000000004 0000000d00000002 R_X86_64_PC32 0000000000000000 __SCT__foo + 1
foos.o:
Relocation section '.rela.static_call_sites' at offset 0x430 contains 4 entries:
Offset Info Type Symbol's Value Symbol's Name + Addend
0000000000000000 0000000100000002 R_X86_64_PC32 0000000000000000 .text + 0
0000000000000004 0000000d00000002 R_X86_64_PC32 0000000000000000 __SCT__foo + 1
0000000000000008 0000000100000002 R_X86_64_PC32 0000000000000000 .text + 1d
000000000000000c 0000000d00000002 R_X86_64_PC32 0000000000000000 __SCT__foo + 1
So we have two patch sites, one in the dead code of the weak foo and one
in the real foo. All is well.
*HOWEVER*, when the toolchain strips unused section symbols it
generates things like this (using new enough binutils):
foo-weak.o:
Relocation section '.rela.static_call_sites' at offset 0x2c8 contains 1 entry:
Offset Info Type Symbol's Value Symbol's Name + Addend
0000000000000000 0000000200000002 R_X86_64_PC32 0000000000000000 foo + 0
0000000000000004 0000000d00000002 R_X86_64_PC32 0000000000000000 __SCT__foo + 1
foo.o:
Relocation section '.rela.static_call_sites' at offset 0x310 contains 2 entries:
Offset Info Type Symbol's Value Symbol's Name + Addend
0000000000000000 0000000200000002 R_X86_64_PC32 0000000000000000 foo + d
0000000000000004 0000000d00000002 R_X86_64_PC32 0000000000000000 __SCT__foo + 1
foos.o:
Relocation section '.rela.static_call_sites' at offset 0x430 contains 4 entries:
Offset Info Type Symbol's Value Symbol's Name + Addend
0000000000000000 0000000100000002 R_X86_64_PC32 0000000000000000 foo + 0
0000000000000004 0000000d00000002 R_X86_64_PC32 0000000000000000 __SCT__foo + 1
0000000000000008 0000000100000002 R_X86_64_PC32 0000000000000000 foo + d
000000000000000c 0000000d00000002 R_X86_64_PC32 0000000000000000 __SCT__foo + 1
And now we can see how that foos.o .static_call_sites goes side-ways, we
now have _two_ patch sites in foo. One for the weak symbol at foo+0
(which is no longer a static_call site!) and one at foo+d which is in
fact the right location.
This seems to happen when objtool cannot find a section symbol, in which
case it falls back to any other symbol to key off of, however in this
case that goes terribly wrong!
As such, teach objtool to create a section symbol when there isn't
one.
Fixes: 44f6a7c075 ("objtool: Fix seg fault with Clang non-section symbols")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20220419203807.655552918@infradead.org
There's a fun implementation detail on linking STB_WEAK symbols. When
the linker combines two translation units, where one contains a weak
function and the other an override for it. It simply strips the
STB_WEAK symbol from the symbol table, but doesn't actually remove the
code.
The result is that when objtool is ran in a whole-archive kind of way,
it will encounter *heaps* of unused (and unreferenced) code. All
rudiments of weak functions.
Additionally, when a weak implementation is split into a .cold
subfunction that .cold symbol is left in place, even though completely
unused.
Teach objtool to ignore such rudiments by searching for symbol holes;
that is, code ranges that fall outside the given symbol bounds.
Specifically, ignore a sequence of unreachable instruction iff they
occupy a single hole, additionally ignore any .cold subfunctions
referenced.
Both ld.bfd and ld.lld behave like this. LTO builds otoh can (and do)
properly DCE weak functions.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154319.232019347@infradead.org
Add a --dry-run argument to skip writing the modifications. This is
convenient for debugging.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154317.282720146@infradead.org
Boris reported that in one of his randconfig builds, objtool got
infinitely stuck. Turns out there's trivial list corruption in the
pv_ops tracking when a function is both in a static table and in a code
assignment.
Avoid re-adding function to the pv_ops[] lists when they're already on
it.
Fixes: db2b0c5d7b ("objtool: Support pv_opsindirect calls for noinstr")
Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Tested-by: Borislav Petkov <bp@alien8.de>
Link: https://lkml.kernel.org/r/20211202204534.GA16608@worktop.programming.kicks-ass.net
- Improve retpoline code patching by separating it from alternatives which
reduces memory footprint and allows to do better optimizations in the
actual runtime patching.
- Add proper retpoline support for x86/BPF
- Address noinstr warnings in x86/kvm, lockdep and paravirtualization code
- Add support to handle pv_opsindirect calls in the noinstr analysis
- Classify symbols upfront and cache the result to avoid redundant
str*cmp() invocations.
- Add a CFI hash to reduce memory consumption which also reduces runtime
on a allyesconfig by ~50%
- Adjust XEN code to make objtool handling more robust and as a side
effect to prevent text fragmentation due to placement of the hypercall
page.
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Merge tag 'objtool-core-2021-10-31' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull objtool updates from Thomas Gleixner:
- Improve retpoline code patching by separating it from alternatives
which reduces memory footprint and allows to do better optimizations
in the actual runtime patching.
- Add proper retpoline support for x86/BPF
- Address noinstr warnings in x86/kvm, lockdep and paravirtualization
code
- Add support to handle pv_opsindirect calls in the noinstr analysis
- Classify symbols upfront and cache the result to avoid redundant
str*cmp() invocations.
- Add a CFI hash to reduce memory consumption which also reduces
runtime on a allyesconfig by ~50%
- Adjust XEN code to make objtool handling more robust and as a side
effect to prevent text fragmentation due to placement of the
hypercall page.
* tag 'objtool-core-2021-10-31' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (41 commits)
bpf,x86: Respect X86_FEATURE_RETPOLINE*
bpf,x86: Simplify computing label offsets
x86,bugs: Unconditionally allow spectre_v2=retpoline,amd
x86/alternative: Add debug prints to apply_retpolines()
x86/alternative: Try inline spectre_v2=retpoline,amd
x86/alternative: Handle Jcc __x86_indirect_thunk_\reg
x86/alternative: Implement .retpoline_sites support
x86/retpoline: Create a retpoline thunk array
x86/retpoline: Move the retpoline thunk declarations to nospec-branch.h
x86/asm: Fixup odd GEN-for-each-reg.h usage
x86/asm: Fix register order
x86/retpoline: Remove unused replacement symbols
objtool,x86: Replace alternatives with .retpoline_sites
objtool: Shrink struct instruction
objtool: Explicitly avoid self modifying code in .altinstr_replacement
objtool: Classify symbols
objtool: Support pv_opsindirect calls for noinstr
x86/xen: Rework the xen_{cpu,irq,mmu}_opsarrays
x86/xen: Mark xen_force_evtchn_callback() noinstr
x86/xen: Make irq_disable() noinstr
...
Instead of writing complete alternatives, simply provide a list of all
the retpoline thunk calls. Then the kernel is free to do with them as
it pleases. Simpler code all-round.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Borislav Petkov <bp@suse.de>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Tested-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/r/20211026120309.850007165@infradead.org
The libelf implementation from elftoolchain has a safety check in
gelf_update_rel[a] to check that the data corresponds to a section
that has type SHT_REL[A] [0]. If the relocation is updated before
the section header is updated with the proper type, this check
fails.
To fix this, update the section header first, before the relocations.
Previously, the section size was calculated in elf_rebuild_reloc_section
by counting the number of entries in the reloc_list. However, we
now need the size during elf_write so instead keep a running total
and add to it for every new relocation.
[0] https://sourceforge.net/p/elftoolchain/mailman/elftoolchain-developers/thread/CAGw6cBtkZro-8wZMD2ULkwJ39J+tHtTtAWXufMjnd3cQ7XG54g@mail.gmail.com/
Signed-off-by: Michael Forney <mforney@mforney.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20210509000103.11008-2-mforney@mforney.org
Otherwise, if these fail we end up with garbage data in the
.rela.orc_unwind_ip section, leading to errors like
ld: fs/squashfs/namei.o: bad reloc symbol index (0x7f16 >= 0x12) for offset 0x7f16d5c82cc8 in section `.orc_unwind_ip'
Signed-off-by: Michael Forney <mforney@mforney.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20210509000103.11008-1-mforney@mforney.org
The section structure already contains sh_size, so just remove the extra
'len' member that requires extra mirroring and potential confusion.
Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20210822225037.54620-3-joe.lawrence@redhat.com
Cc: Andy Lavr <andy.lavr@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org
kernel tooling such as kpatch-build.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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mergetag object d33b9035e1
type commit
tag objtool-core-2021-06-28
tagger Ingo Molnar <mingo@kernel.org> 1624859477 +0200
The biggest change in this cycle is the new code to handle
and rewrite variable sized jump labels - which results in
slightly tighter code generation in hot paths, through the
use of short(er) NOPs.
Also a number of cleanups and fixes, and a change to the
generic include/linux/compiler.h to handle a s390 GCC quirk.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tags 'objtool-urgent-2021-06-28' and 'objtool-core-2021-06-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull objtool fix and updates from Ingo Molnar:
"An ELF format fix for a section flags mismatch bug that breaks kernel
tooling such as kpatch-build.
The biggest change in this cycle is the new code to handle and rewrite
variable sized jump labels - which results in slightly tighter code
generation in hot paths, through the use of short(er) NOPs.
Also a number of cleanups and fixes, and a change to the generic
include/linux/compiler.h to handle a s390 GCC quirk"
* tag 'objtool-urgent-2021-06-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
objtool: Don't make .altinstructions writable
* tag 'objtool-core-2021-06-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
objtool: Improve reloc hash size guestimate
instrumentation.h: Avoid using inline asm operand modifiers
compiler.h: Avoid using inline asm operand modifiers
kbuild: Fix objtool dependency for 'OBJECT_FILES_NON_STANDARD_<obj> := n'
objtool: Reflow handle_jump_alt()
jump_label/x86: Remove unused JUMP_LABEL_NOP_SIZE
jump_label, x86: Allow short NOPs
objtool: Provide stats for jump_labels
objtool: Rewrite jump_label instructions
objtool: Decode jump_entry::key addend
jump_label, x86: Emit short JMP
jump_label: Free jump_entry::key bit1 for build use
jump_label, x86: Add variable length patching support
jump_label, x86: Introduce jump_entry_size()
jump_label, x86: Improve error when we fail expected text
jump_label, x86: Factor out the __jump_table generation
jump_label, x86: Strip ASM jump_label support
x86, objtool: Dont exclude arch/x86/realmode/
objtool: Rewrite hashtable sizing
Nathan reported that LLVM ThinLTO builds have a performance regression
with commit 25cf0d8aa2 ("objtool: Rewrite hashtable sizing"). Sami
was quick to note that this is due to their use of -ffunction-sections.
As a result the .text section is small and basing the number of relocs
off of that no longer works. Instead have read_sections() compute the
sum of all SHF_EXECINSTR sections and use that.
Fixes: 25cf0d8aa2 ("objtool: Rewrite hashtable sizing")
Reported-by: Nathan Chancellor <nathan@kernel.org>
Debugged-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lkml.kernel.org/r/YMJpGLuGNsGtA5JJ@hirez.programming.kicks-ass.net
When an ELF object uses extended symbol section indexes (IOW it has a
.symtab_shndx section), these must be kept in sync with the regular
symbol table (.symtab).
So for every new symbol we emit, make sure to also emit a
.symtab_shndx value to keep the arrays of equal size.
Note: since we're writing an UNDEF symbol, most GElf_Sym fields will
be 0 and we can repurpose one (st_size) to host the 0 for the xshndx
value.
Fixes: 2f2f7e47f0 ("objtool: Add elf_create_undef_symbol()")
Reported-by: Nick Desaulniers <ndesaulniers@google.com>
Suggested-by: Fangrui Song <maskray@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lkml.kernel.org/r/YL3q1qFO9QIRL/BA@hirez.programming.kicks-ass.net
Currently x86 cross-compilation fails on big endian system with:
x86_64-cross-ld: init/main.o: invalid string offset 488112128 >= 6229 for section `.strtab'
Mark new ELF data in elf_create_undef_symbol() as symbol, so that libelf
does endianness handling correctly.
Fixes: 2f2f7e47f0 ("objtool: Add elf_create_undef_symbol()")
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: https://lore.kernel.org/r/patch-1.thread-6c9df9.git-d39264656387.your-ad-here.call-01620841104-ext-2554@work.hours
Currently objtool has 5 hashtables and sizes them 16 or 20 bits
depending on the --vmlinux argument.
However, a single side doesn't really work well for the 5 tables,
which among them, cover 3 different uses. Also, while vmlinux is
larger, there is still a very wide difference between a defconfig and
allyesconfig build, which again isn't optimally covered by a single
size.
Another aspect is the cost of elf_hash_init(), which for large tables
dominates the runtime for small input files. It turns out that all it
does it assign NULL, something that is required when using malloc().
However, when we allocate memory using mmap(), we're guaranteed to get
zero filled pages.
Therefore, rewrite the whole thing to:
1) use more dynamic sized tables, depending on the input file,
2) avoid the need for elf_hash_init() entirely by using mmap().
This speeds up a regular kernel build (100s to 98s for
x86_64-defconfig), and potentially dramatically speeds up vmlinux
processing.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210506194157.452881700@infradead.org
Allow objtool to create undefined symbols; this allows creating
relocations to symbols not currently in the symbol table.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Link: https://lkml.kernel.org/r/20210326151300.064743095@infradead.org
Create a common helper to append strings to a strtab.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Link: https://lkml.kernel.org/r/20210326151259.941474004@infradead.org
We have 4 instances of adding a relocation. Create a common helper
to avoid growing even more.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Link: https://lkml.kernel.org/r/20210326151259.817438847@infradead.org
Instead of manually calling elf_rebuild_reloc_section() on sections
we've called elf_add_reloc() on, have elf_write() DTRT.
This makes it easier to add random relocations in places without
carefully tracking when we're done and need to flush what section.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Link: https://lkml.kernel.org/r/20210326151259.754213408@infradead.org
- Make objtool work for big-endian cross compiles
- Make stack tracking via stack pointer memory operations match push/pop
semantics to prepare for architectures w/o PUSH/POP instructions.
- Add support for analyzing alternatives
- Improve retpoline detection and handling
- Improve assembly code coverage on x86
- Provide support for inlined stack switching
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Merge tag 'objtool-core-2021-02-23' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull objtool updates from Thomas Gleixner:
- Make objtool work for big-endian cross compiles
- Make stack tracking via stack pointer memory operations match
push/pop semantics to prepare for architectures w/o PUSH/POP
instructions.
- Add support for analyzing alternatives
- Improve retpoline detection and handling
- Improve assembly code coverage on x86
- Provide support for inlined stack switching
* tag 'objtool-core-2021-02-23' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (33 commits)
objtool: Support stack-swizzle
objtool,x86: Additionally decode: mov %rsp, (%reg)
x86/unwind/orc: Change REG_SP_INDIRECT
x86/power: Support objtool validation in hibernate_asm_64.S
x86/power: Move restore_registers() to top of the file
x86/power: Annotate indirect branches as safe
x86/acpi: Support objtool validation in wakeup_64.S
x86/acpi: Annotate indirect branch as safe
x86/ftrace: Support objtool vmlinux.o validation in ftrace_64.S
x86/xen/pvh: Annotate indirect branch as safe
x86/xen: Support objtool vmlinux.o validation in xen-head.S
x86/xen: Support objtool validation in xen-asm.S
objtool: Add xen_start_kernel() to noreturn list
objtool: Combine UNWIND_HINT_RET_OFFSET and UNWIND_HINT_FUNC
objtool: Add asm version of STACK_FRAME_NON_STANDARD
objtool: Assume only ELF functions do sibling calls
x86/ftrace: Add UNWIND_HINT_FUNC annotation for ftrace_stub
objtool: Support retpoline jump detection for vmlinux.o
objtool: Fix ".cold" section suffix check for newer versions of GCC
objtool: Fix retpoline detection in asm code
...
I've always been bothered by the endless (fragile) boilerplate for
rbtree, and I recently wrote some rbtree helpers for objtool and
figured I should lift them into the kernel and use them more widely.
Provide:
partial-order; less() based:
- rb_add(): add a new entry to the rbtree
- rb_add_cached(): like rb_add(), but for a rb_root_cached
total-order; cmp() based:
- rb_find(): find an entry in an rbtree
- rb_find_add(): find an entry, and add if not found
- rb_find_first(): find the first (leftmost) matching entry
- rb_next_match(): continue from rb_find_first()
- rb_for_each(): iterate a sub-tree using the previous two
Inlining and constant propagation should see the compiler inline the
whole thing, including the various compare functions.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Michel Lespinasse <walken@google.com>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Thanks to a recent binutils change which doesn't generate unused
symbols, it's now possible for thunk_64.o be completely empty without
CONFIG_PREEMPTION: no text, no data, no symbols.
We could edit the Makefile to only build that file when
CONFIG_PREEMPTION is enabled, but that will likely create confusion
if/when the thunks end up getting used by some other code again.
Just ignore it and move on.
Reported-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Tested-by: Nathan Chancellor <natechancellor@gmail.com>
Link: https://github.com/ClangBuiltLinux/linux/issues/1254
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Currently objtool headers are being included either by their base name
or included via ../ from a parent directory. In case of a base name usage:
#include "warn.h"
#include "arch_elf.h"
it does not make it apparent from which directory the file comes from.
To make it slightly better, and actually to avoid name clashes some arch
specific files have "arch_" suffix. And files from an arch folder have
to revert to including via ../ e.g:
#include "../../elf.h"
With additional architectures support and the code base growth there is
a need for clearer headers naming scheme for multiple reasons:
1. to make it instantly obvious where these files come from (objtool
itself / objtool arch|generic folders / some other external files),
2. to avoid name clashes of objtool arch specific headers, potential
obtool arch generic headers and the system header files (there is
/usr/include/elf.h already),
3. to avoid ../ includes and improve code readability.
4. to give a warm fuzzy feeling to developers who are mostly kernel
developers and are accustomed to linux kernel headers arranging
scheme.
Doesn't this make it instantly obvious where are these files come from?
#include <objtool/warn.h>
#include <arch/elf.h>
And doesn't it look nicer to avoid ugly ../ includes? Which also
guarantees this is elf.h from the objtool and not /usr/include/elf.h.
#include <objtool/elf.h>
This patch defines and implements new objtool headers arranging
scheme. Which is:
- all generic headers go to include/objtool (similar to include/linux)
- all arch headers go to arch/$(SRCARCH)/include/arch (to get arch
prefix). This is similar to linux arch specific "asm/*" headers but we
are not abusing "asm" name and calling it what it is. This also helps
to prevent name clashes (arch is not used in system headers or kernel
exports).
To bring objtool to this state the following things are done:
1. current top level tools/objtool/ headers are moved into
include/objtool/ subdirectory,
2. arch specific headers, currently only arch/x86/include/ are moved into
arch/x86/include/arch/ and were stripped of "arch_" suffix,
3. new -I$(srctree)/tools/objtool/include include path to make
includes like <objtool/warn.h> possible,
4. rewriting file includes,
5. make git not to ignore include/objtool/ subdirectory.
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Relocations generated in elf_rebuild_rel[a]_reloc_section() are broken
if objtool is built and run on a big endian system.
The following errors pop up during x86 cross-compilation:
x86_64-9.1.0-ld: fs/efivarfs/inode.o: bad reloc symbol index (0x2000000 >= 0x22) for offset 0 in section `.orc_unwind_ip'
x86_64-9.1.0-ld: final link failed: bad value
Convert those functions to use gelf_update_rel[a](), similar to what
elf_write_reloc() does.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Co-developed-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Building with the Clang assembler shows the following warning:
arch/x86/kernel/ftrace_64.o: warning: objtool: missing symbol for insn at offset 0x16
The Clang assembler strips section symbols. That ends up giving
objtool's find_func_containing() much more test coverage than normal.
Turns out, find_func_containing() doesn't work so well for overlapping
symbols:
2: 000000000000000e 0 NOTYPE LOCAL DEFAULT 2 fgraph_trace
3: 000000000000000f 0 NOTYPE LOCAL DEFAULT 2 trace
4: 0000000000000000 165 FUNC GLOBAL DEFAULT 2 __fentry__
5: 000000000000000e 0 NOTYPE GLOBAL DEFAULT 2 ftrace_stub
The zero-length NOTYPE symbols are inside __fentry__(), confusing the
rbtree search for any __fentry__() offset coming after a NOTYPE.
Try to avoid this problem by not adding zero-length symbols to the
rbtree. They're rare and aren't needed in the rbtree anyway.
One caveat, this actually might not end up being the right fix.
Non-empty overlapping symbols, if they exist, could have the same
problem. But that would need bigger changes, let's see if we can get
away with the easy fix for now.
Reported-by: Arnd Bergmann <arnd@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
The Clang assembler likes to strip section symbols, which means objtool
can't reference some text code by its section. This confuses objtool
greatly, causing it to seg fault.
The fix is similar to what was done before, for ORC reloc generation:
e81e072443 ("objtool: Support Clang non-section symbols in ORC generation")
Factor out that code into a common helper and use it for static call
reloc generation as well.
Reported-by: Arnd Bergmann <arnd@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Link: https://github.com/ClangBuiltLinux/linux/issues/1207
Link: https://lkml.kernel.org/r/ba6b6c0f0dd5acbba66e403955a967d9fdd1726a.1607983452.git.jpoimboe@redhat.com
Add the inline static call implementation for x86-64. The generated code
is identical to the out-of-line case, except we move the trampoline into
it's own section.
Objtool uses the trampoline naming convention to detect all the call
sites. It then annotates those call sites in the .static_call_sites
section.
During boot (and module init), the call sites are patched to call
directly into the destination function. The temporary trampoline is
then no longer used.
[peterz: merged trampolines, put trampoline in section]
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20200818135804.864271425@infradead.org
This provides infrastructure to rewrite instructions; this is
immediately useful for helping out with KCOV-vs-noinstr, but will
also come in handy for a bunch of variable sized jump-label patches
that are still on ice.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
With there being multiple ways to change the ELF data, let's more
concisely track modification.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Currently objtool only collects information about relocations with
addends. In recordmcount, which we are about to merge into objtool,
some supported architectures do not use rela relocations.
Signed-off-by: Matt Helsley <mhelsley@vmware.com>
Reviewed-by: Julien Thierry <jthierry@redhat.com>
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Before supporting additional relocation types rename the relevant
types and functions from "rela" to "reloc". This work be done with
the following regex:
sed -e 's/struct rela/struct reloc/g' \
-e 's/\([_\*]\)rela\(s\{0,1\}\)/\1reloc\2/g' \
-e 's/tmprela\(s\{0,1\}\)/tmpreloc\1/g' \
-e 's/relasec/relocsec/g' \
-e 's/rela_list/reloc_list/g' \
-e 's/rela_hash/reloc_hash/g' \
-e 's/add_rela/add_reloc/g' \
-e 's/rela->/reloc->/g' \
-e '/rela[,\.]/{ s/\([^\.>]\)rela\([\.,]\)/\1reloc\2/g ; }' \
-e 's/rela =/reloc =/g' \
-e 's/relas =/relocs =/g' \
-e 's/relas\[/relocs[/g' \
-e 's/relaname =/relocname =/g' \
-e 's/= rela\;/= reloc\;/g' \
-e 's/= relas\;/= relocs\;/g' \
-e 's/= relaname\;/= relocname\;/g' \
-e 's/, rela)/, reloc)/g' \
-e 's/\([ @]\)rela\([ "]\)/\1reloc\2/g' \
-e 's/ rela$/ reloc/g' \
-e 's/, relaname/, relocname/g' \
-e 's/sec->rela/sec->reloc/g' \
-e 's/(\(!\{0,1\}\)rela/(\1reloc/g' \
-i \
arch.h \
arch/x86/decode.c \
check.c \
check.h \
elf.c \
elf.h \
orc_gen.c \
special.c
Notable exceptions which complicate the regex include gelf_*
library calls and standard/expected section names which still use
"rela" because they encode the type of relocation expected. Also, keep
"rela" in the struct because it encodes a specific type of relocation
we currently expect.
It will eventually turn into a member of an anonymous union when a
susequent patch adds implicit addend, or "rel", relocation support.
Signed-off-by: Matt Helsley <mhelsley@vmware.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
ELF doesn't require .rela section names to match the base section. Use
the section index in sh_info to find the section instead of looking it
up by name.
LLD, for example, generates a .rela section that doesn't match the base
section name when we merge sections in a linker script for a binary
compiled with -ffunction-sections.
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
If a .cold function is examined prior to it's parent, the link
to the parent/child function can be overwritten when the parent
is examined. Only update pfunc and cfunc if they were previously
nil to prevent this from happening.
This fixes an issue seen when compiling with -ffunction-sections.
Signed-off-by: Kristen Carlson Accardi <kristen@linux.intel.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Currently, objtool fails to load the correct section for symbols when
the index is greater than SHN_LORESERVE. Use gelf_getsymshndx instead
of gelf_getsym to handle >64k sections.
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20200421220843.188260-2-samitolvanen@google.com
Quoting Julien:
"And the other suggestion is my other email was that you don't even
need to add INSN_EXCEPTION_RETURN. You can keep IRET as
INSN_CONTEXT_SWITCH by default and x86 decoder lookups the symbol
conaining an iret. If it's a function symbol, it can just set the type
to INSN_OTHER so that it caries on to the next instruction after
having handled the stack_op."
Suggested-by: Julien Thierry <jthierry@redhat.com>
Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20200428191659.913283807@infradead.org
In preparation to parallelize certain parts of objtool, map out which uses
of various data structures are read-only vs. read-write.
As a first step constify 'struct elf' pointer passing, most of the secondary
uses of it in find_symbol_*() methods are read-only.
Also, while at it, better group the 'struct elf' handling methods in elf.h.
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sami Tolvanen <samitolvanen@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20200422103205.61900-2-mingo@kernel.org
When doing kbuild tests to see if the objtool changes affected those I
found that there was a measurable regression:
pre post
real 1m13.594 1m16.488s
user 34m58.246s 35m23.947s
sys 4m0.393s 4m27.312s
Perf showed that for small files the increased hash-table sizes were a
measurable difference. Since we already have -l "vmlinux" to
distinguish between the modes, make it also use a smaller portion of
the hash-tables.
This flips it into a small win:
real 1m14.143s
user 34m49.292s
sys 3m44.746s
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20200416115119.167588731@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Sometimes, WARN_FUNC() and other users of symbol_by_offset() will
associate the first instruction of a symbol with the symbol preceding
it. This is because symbol->offset + symbol->len is already outside of
the symbol's range.
Fixes: 2a362ecc3e ("objtool: Optimize find_symbol_*() and read_symbols()")
Signed-off-by: Julien Thierry <jthierry@redhat.com>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Perf shows there is significant time in find_rela_by_dest(); this is
because we have to iterate the address space per byte, looking for
relocation entries.
Optimize this by reducing the address space granularity.
This reduces objtool on vmlinux.o runtime from 4.8 to 4.4 seconds.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20200324160924.861321325@infradead.org
Perf showed that __hash_init() is a significant portion of
read_sections(), so instead of doing a per section rela_hash, use an
elf-wide rela_hash.
Statistics show us there are about 1.1 million relas, so size it
accordingly.
This reduces the objtool on vmlinux.o runtime to a third, from 15 to 5
seconds.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20200324160924.739153726@infradead.org
Perf showed that find_symbol_by_name() takes time; add a symbol name
hash.
This shaves another second off of objtool on vmlinux.o runtime, down
to 15 seconds.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20200324160924.676865656@infradead.org
