Pull objtool fixes from Ingo Molnar:
"Fix an objtool false positive, and objtool related build warnings that
happens on PIE-enabled architectures such as LoongArch"
* tag 'objtool-urgent-2025-02-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
objtool: Add bch2_trans_unlocked_or_in_restart_error() to bcachefs noreturns
objtool: Fix C jump table annotations for Clang
vmlinux.lds: Ensure that const vars with relocations are mapped R/O
A C jump table (such as the one used by the BPF interpreter) is a const
global array of absolute code addresses, and this means that the actual
values in the table may not be known until the kernel is booted (e.g.,
when using KASLR or when the kernel VA space is sized dynamically).
When using PIE codegen, the compiler will default to placing such const
global objects in .data.rel.ro (which is annotated as writable), rather
than .rodata (which is annotated as read-only). As C jump tables are
explicitly emitted into .rodata, this used to result in warnings for
LoongArch builds (which uses PIE codegen for the entire kernel) like
Warning: setting incorrect section attributes for .rodata..c_jump_table
due to the fact that the explicitly specified .rodata section inherited
the read-write annotation that the compiler uses for such objects when
using PIE codegen.
This warning was suppressed by explicitly adding the read-only
annotation to the __attribute__((section(""))) string, by commit
c5b1184dec ("compiler.h: specify correct attribute for .rodata..c_jump_table")
Unfortunately, this hack does not work on Clang's integrated assembler,
which happily interprets the appended section type and permission
specifiers as part of the section name, which therefore no longer
matches the hard-coded pattern '.rodata..c_jump_table' that objtool
expects, causing it to emit a warning
kernel/bpf/core.o: warning: objtool: ___bpf_prog_run+0x20: sibling call from callable instruction with modified stack frame
Work around this, by emitting C jump tables into .data.rel.ro instead,
which is treated as .rodata by the linker script for all builds, not
just PIE based ones.
Fixes: c5b1184dec ("compiler.h: specify correct attribute for .rodata..c_jump_table")
Tested-by: Tiezhu Yang <yangtiezhu@loongson.cn> # on LoongArch
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20250221135704.431269-6-ardb+git@google.com
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Pull objtool fixes from Borislav Petkov:
- Move a warning about a lld.ld breakage into the verbose setting as
said breakage has been fixed in the meantime
- Teach objtool to ignore dangling jump table entries added by Clang
* tag 'objtool_urgent_for_v6.14_rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
objtool: Move dodgy linker warn to verbose
objtool: Ignore dangling jump table entries
Starting with Rust 1.85.0 (currently in beta, to be released 2025-02-20),
under some kernel configurations with `CONFIG_RUST_DEBUG_ASSERTIONS=y`,
one may trigger a new `objtool` warning:
rust/kernel.o: warning: objtool: _R...securityNtB2_11SecurityCtx8as_bytes()
falls through to next function _R...core3ops4drop4Drop4drop()
due to a call to the `noreturn` symbol:
core::panicking::assert_failed::<usize, usize>
Thus add it to the list so that `objtool` knows it is actually `noreturn`.
Do so matching with `strstr` since it is a generic.
See commit 56d680dd23 ("objtool/rust: list `noreturn` Rust functions")
for more details.
Cc: stable@vger.kernel.org # Needed in 6.12.y and 6.13.y only (Rust is pinned in older LTSs).
Fixes: 56d680dd23 ("objtool/rust: list `noreturn` Rust functions")
Reviewed-by: Gary Guo <gary@garyguo.net>
Link: https://lore.kernel.org/r/20250112143951.751139-1-ojeda@kernel.org
[ Updated Cc: stable@ to include 6.13.y. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
The lld.ld borkage is fixed in the latest llvm release (?) but will
not be backported, meaning we're stuck with broken linker for a fair
while.
Lets not spam all clang build logs and move warning to verbose.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
The syscall instruction is used in Xen PV mode for doing hypercalls.
Allow syscall to be used in the kernel in case it is tagged with an
unwind hint for objtool.
This is part of XSA-466 / CVE-2024-53241.
Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Co-developed-by: Peter Zijlstra <peterz@infradead.org>
In preparation for adding support for annotated jump tables, where
ELF relocations and symbols are used to describe the locations of jump
tables in the executable, refactor the jump table discovery logic so the
table size can be returned from arch_find_switch_table().
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20241011170847.334429-12-ardb+git@google.com
Pull Kbuild updates from Masahiro Yamada:
- Add generic support for built-in boot DTB files
- Enable TAB cycling for dialog buttons in nconfig
- Fix issues in streamline_config.pl
- Refactor Kconfig
- Add support for Clang's AutoFDO (Automatic Feedback-Directed
Optimization)
- Add support for Clang's Propeller, a profile-guided optimization.
- Change the working directory to the external module directory for M=
builds
- Support building external modules in a separate output directory
- Enable objtool for *.mod.o and additional kernel objects
- Use lz4 instead of deprecated lz4c
- Work around a performance issue with "git describe"
- Refactor modpost
* tag 'kbuild-v6.13' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild: (85 commits)
kbuild: rename .tmp_vmlinux.kallsyms0.syms to .tmp_vmlinux0.syms
gitignore: Don't ignore 'tags' directory
kbuild: add dependency from vmlinux to resolve_btfids
modpost: replace tdb_hash() with hash_str()
kbuild: deb-pkg: add python3:native to build dependency
genksyms: reduce indentation in export_symbol()
modpost: improve error messages in device_id_check()
modpost: rename alias symbol for MODULE_DEVICE_TABLE()
modpost: rename variables in handle_moddevtable()
modpost: move strstarts() to modpost.h
modpost: convert do_usb_table() to a generic handler
modpost: convert do_of_table() to a generic handler
modpost: convert do_pnp_device_entry() to a generic handler
modpost: convert do_pnp_card_entries() to a generic handler
modpost: call module_alias_printf() from all do_*_entry() functions
modpost: pass (struct module *) to do_*_entry() functions
modpost: remove DEF_FIELD_ADDR_VAR() macro
modpost: deduplicate MODULE_ALIAS() for all drivers
modpost: introduce module_alias_printf() helper
modpost: remove unnecessary check in do_acpi_entry()
...
Add the build support for using Clang's Propeller optimizer. Like
AutoFDO, Propeller uses hardware sampling to gather information
about the frequency of execution of different code paths within a
binary. This information is then used to guide the compiler's
optimization decisions, resulting in a more efficient binary.
The support requires a Clang compiler LLVM 19 or later, and the
create_llvm_prof tool
(https://github.com/google/autofdo/releases/tag/v0.30.1). This
commit is limited to x86 platforms that support PMU features
like LBR on Intel machines and AMD Zen3 BRS.
Here is an example workflow for building an AutoFDO+Propeller
optimized kernel:
1) Build the kernel on the host machine, with AutoFDO and Propeller
build config
CONFIG_AUTOFDO_CLANG=y
CONFIG_PROPELLER_CLANG=y
then
$ make LLVM=1 CLANG_AUTOFDO_PROFILE=<autofdo_profile>
“<autofdo_profile>” is the profile collected when doing a non-Propeller
AutoFDO build. This step builds a kernel that has the same optimization
level as AutoFDO, plus a metadata section that records basic block
information. This kernel image runs as fast as an AutoFDO optimized
kernel.
2) Install the kernel on test/production machines.
3) Run the load tests. The '-c' option in perf specifies the sample
event period. We suggest using a suitable prime number,
like 500009, for this purpose.
For Intel platforms:
$ perf record -e BR_INST_RETIRED.NEAR_TAKEN:k -a -N -b -c <count> \
-o <perf_file> -- <loadtest>
For AMD platforms:
The supported system are: Zen3 with BRS, or Zen4 with amd_lbr_v2
# To see if Zen3 support LBR:
$ cat proc/cpuinfo | grep " brs"
# To see if Zen4 support LBR:
$ cat proc/cpuinfo | grep amd_lbr_v2
# If the result is yes, then collect the profile using:
$ perf record --pfm-events RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k -a \
-N -b -c <count> -o <perf_file> -- <loadtest>
4) (Optional) Download the raw perf file to the host machine.
5) Generate Propeller profile:
$ create_llvm_prof --binary=<vmlinux> --profile=<perf_file> \
--format=propeller --propeller_output_module_name \
--out=<propeller_profile_prefix>_cc_profile.txt \
--propeller_symorder=<propeller_profile_prefix>_ld_profile.txt
“create_llvm_prof” is the profile conversion tool, and a prebuilt
binary for linux can be found on
https://github.com/google/autofdo/releases/tag/v0.30.1 (can also build
from source).
"<propeller_profile_prefix>" can be something like
"/home/user/dir/any_string".
This command generates a pair of Propeller profiles:
"<propeller_profile_prefix>_cc_profile.txt" and
"<propeller_profile_prefix>_ld_profile.txt".
6) Rebuild the kernel using the AutoFDO and Propeller profile files.
CONFIG_AUTOFDO_CLANG=y
CONFIG_PROPELLER_CLANG=y
and
$ make LLVM=1 CLANG_AUTOFDO_PROFILE=<autofdo_profile> \
CLANG_PROPELLER_PROFILE_PREFIX=<propeller_profile_prefix>
Co-developed-by: Han Shen <shenhan@google.com>
Signed-off-by: Han Shen <shenhan@google.com>
Signed-off-by: Rong Xu <xur@google.com>
Suggested-by: Sriraman Tallam <tmsriram@google.com>
Suggested-by: Krzysztof Pszeniczny <kpszeniczny@google.com>
Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
Suggested-by: Stephane Eranian <eranian@google.com>
Tested-by: Yonghong Song <yonghong.song@linux.dev>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Kees Cook <kees@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
For some, as of yet unexplained reason, Clang-19, but not GCC,
generates and endless stream of:
drivers/iio/imu/bno055/bno055_ser.o: warning: objtool: __tracepoint_send_chunk+0x20: data relocation to !ENDBR: __SCT__tp_func_send_chunk+0x0
drivers/iio/imu/bno055/bno055_ser.o: warning: objtool: __tracepoint_cmd_retry+0x20: data relocation to !ENDBR: __SCT__tp_func_cmd_retry+0x0
drivers/iio/imu/bno055/bno055_ser.o: warning: objtool: __tracepoint_write_reg+0x20: data relocation to !ENDBR: __SCT__tp_func_write_reg+0x0
drivers/iio/imu/bno055/bno055_ser.o: warning: objtool: __tracepoint_read_reg+0x20: data relocation to !ENDBR: __SCT__tp_func_read_reg+0x0
drivers/iio/imu/bno055/bno055_ser.o: warning: objtool: __tracepoint_recv+0x20: data relocation to !ENDBR: __SCT__tp_func_recv+0x0
Which is entirely correct, but harmless. Add the __tracepoints section
to the exclusion list.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20241108184618.GG38786@noisy.programming.kicks-ass.net
Add the build support for using Clang's AutoFDO. Building the kernel
with AutoFDO does not reduce the optimization level from the
compiler. AutoFDO uses hardware sampling to gather information about
the frequency of execution of different code paths within a binary.
This information is then used to guide the compiler's optimization
decisions, resulting in a more efficient binary. Experiments
showed that the kernel can improve up to 10% in latency.
The support requires a Clang compiler after LLVM 17. This submission
is limited to x86 platforms that support PMU features like LBR on
Intel machines and AMD Zen3 BRS. Support for SPE on ARM 1,
and BRBE on ARM 1 is part of planned future work.
Here is an example workflow for AutoFDO kernel:
1) Build the kernel on the host machine with LLVM enabled, for example,
$ make menuconfig LLVM=1
Turn on AutoFDO build config:
CONFIG_AUTOFDO_CLANG=y
With a configuration that has LLVM enabled, use the following
command:
scripts/config -e AUTOFDO_CLANG
After getting the config, build with
$ make LLVM=1
2) Install the kernel on the test machine.
3) Run the load tests. The '-c' option in perf specifies the sample
event period. We suggest using a suitable prime number,
like 500009, for this purpose.
For Intel platforms:
$ perf record -e BR_INST_RETIRED.NEAR_TAKEN:k -a -N -b -c <count> \
-o <perf_file> -- <loadtest>
For AMD platforms:
The supported system are: Zen3 with BRS, or Zen4 with amd_lbr_v2
For Zen3:
$ cat proc/cpuinfo | grep " brs"
For Zen4:
$ cat proc/cpuinfo | grep amd_lbr_v2
$ perf record --pfm-events RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k -a \
-N -b -c <count> -o <perf_file> -- <loadtest>
4) (Optional) Download the raw perf file to the host machine.
5) To generate an AutoFDO profile, two offline tools are available:
create_llvm_prof and llvm_profgen. The create_llvm_prof tool is part
of the AutoFDO project and can be found on GitHub
(https://github.com/google/autofdo), version v0.30.1 or later. The
llvm_profgen tool is included in the LLVM compiler itself. It's
important to note that the version of llvm_profgen doesn't need to
match the version of Clang. It needs to be the LLVM 19 release or
later, or from the LLVM trunk.
$ llvm-profgen --kernel --binary=<vmlinux> --perfdata=<perf_file> \
-o <profile_file>
or
$ create_llvm_prof --binary=<vmlinux> --profile=<perf_file> \
--format=extbinary --out=<profile_file>
Note that multiple AutoFDO profile files can be merged into one via:
$ llvm-profdata merge -o <profile_file> <profile_1> ... <profile_n>
6) Rebuild the kernel using the AutoFDO profile file with the same config
as step 1, (Note CONFIG_AUTOFDO_CLANG needs to be enabled):
$ make LLVM=1 CLANG_AUTOFDO_PROFILE=<profile_file>
Co-developed-by: Han Shen <shenhan@google.com>
Signed-off-by: Han Shen <shenhan@google.com>
Signed-off-by: Rong Xu <xur@google.com>
Suggested-by: Sriraman Tallam <tmsriram@google.com>
Suggested-by: Krzysztof Pszeniczny <kpszeniczny@google.com>
Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
Suggested-by: Stephane Eranian <eranian@google.com>
Tested-by: Yonghong Song <yonghong.song@linux.dev>
Tested-by: Yabin Cui <yabinc@google.com>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Kees Cook <kees@kernel.org>
Tested-by: Peter Jung <ptr1337@cachyos.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
