Re: [PATCH v2 bpf-next 1/3] objtool: Copy noreturns.h to include/linux

[Alexei Starovoitov]

On Sat, Feb 22, 2025 at 10:28 PM Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
>
> It will used by bpf to reject attaching fexit prog to functions
> annotated with __noreturn.
>
> Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> ---
>  include/linux/noreturns.h               | 52 +++++++++++++++++++++++++
>  tools/objtool/Documentation/objtool.txt |  3 +-
>  tools/objtool/sync-check.sh             |  2 +
>  3 files changed, 56 insertions(+), 1 deletion(-)
>  create mode 100644 include/linux/noreturns.h
>
> diff --git a/include/linux/noreturns.h b/include/linux/noreturns.h
> new file mode 100644
> index 000000000000..b2174894f9f7
> --- /dev/null
> +++ b/include/linux/noreturns.h
> @@ -0,0 +1,52 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +/*
> + * This is a (sorted!) list of all known __noreturn functions in the kernel.
> + * It's needed for objtool to properly reverse-engineer the control flow graph.
> + *
> + * Yes, this is unfortunate.  A better solution is in the works.
> + */
> +NORETURN(__fortify_panic)
> +NORETURN(__ia32_sys_exit)
> +NORETURN(__ia32_sys_exit_group)
> +NORETURN(__kunit_abort)
> +NORETURN(__module_put_and_kthread_exit)
> +NORETURN(__stack_chk_fail)
> +NORETURN(__tdx_hypercall_failed)
> +NORETURN(__ubsan_handle_builtin_unreachable)
> +NORETURN(__x64_sys_exit)
> +NORETURN(__x64_sys_exit_group)
> +NORETURN(arch_cpu_idle_dead)
> +NORETURN(bch2_trans_in_restart_error)
> +NORETURN(bch2_trans_restart_error)
> +NORETURN(bch2_trans_unlocked_error)
> +NORETURN(cpu_bringup_and_idle)
> +NORETURN(cpu_startup_entry)
> +NORETURN(do_exit)
> +NORETURN(do_group_exit)
> +NORETURN(do_task_dead)
> +NORETURN(ex_handler_msr_mce)
> +NORETURN(hlt_play_dead)
> +NORETURN(hv_ghcb_terminate)
> +NORETURN(kthread_complete_and_exit)
> +NORETURN(kthread_exit)
> +NORETURN(kunit_try_catch_throw)
> +NORETURN(machine_real_restart)
> +NORETURN(make_task_dead)
> +NORETURN(mpt_halt_firmware)
> +NORETURN(nmi_panic_self_stop)
> +NORETURN(panic)
> +NORETURN(panic_smp_self_stop)
> +NORETURN(rest_init)
> +NORETURN(rewind_stack_and_make_dead)
> +NORETURN(rust_begin_unwind)
> +NORETURN(rust_helper_BUG)
> +NORETURN(sev_es_terminate)
> +NORETURN(snp_abort)
> +NORETURN(start_kernel)
> +NORETURN(stop_this_cpu)
> +NORETURN(usercopy_abort)
> +NORETURN(x86_64_start_kernel)
> +NORETURN(x86_64_start_reservations)
> +NORETURN(xen_cpu_bringup_again)
> +NORETURN(xen_start_kernel)
> diff --git a/tools/objtool/Documentation/objtool.txt b/tools/objtool/Documentation/objtool.txt
> index 7c3ee959b63c..70a878e4dc36 100644
> --- a/tools/objtool/Documentation/objtool.txt
> +++ b/tools/objtool/Documentation/objtool.txt
> @@ -326,7 +326,8 @@ the objtool maintainers.
>
>     The call from foo() to bar() doesn't return, but bar() is missing the
>     __noreturn annotation.  NOTE: In addition to annotating the function
> -   with __noreturn, please also add it to tools/objtool/noreturns.h.
> +   with __noreturn, please also add it to tools/objtool/noreturns.h and
> +   include/linux/noreturns.h.
>
>  4. file.o: warning: objtool: func(): can't find starting instruction
>     or
> diff --git a/tools/objtool/sync-check.sh b/tools/objtool/sync-check.sh
> index 81d120d05442..23b9813cd5e9 100755
> --- a/tools/objtool/sync-check.sh
> +++ b/tools/objtool/sync-check.sh
> @@ -17,6 +17,7 @@ arch/x86/include/asm/emulate_prefix.h
>  arch/x86/lib/x86-opcode-map.txt
>  arch/x86/tools/gen-insn-attr-x86.awk
>  include/linux/static_call_types.h
> +tools/objtool/noreturns.h
>  "
>
>  SYNC_CHECK_FILES='
> @@ -24,6 +25,7 @@ arch/x86/include/asm/inat.h
>  arch/x86/include/asm/insn.h
>  arch/x86/lib/inat.c
>  arch/x86/lib/insn.c
> +include/linux/noreturns.h

The copy looks pointless.
Since we cannot rely on objtool let's just list all noreturn funcs
directly in BTF_SET_START(fexit_deny) in a single patch.
So all changes will be under kernel/bpf directory.

pw-bot: cr