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

[Yafang Shao]

On Mon, Feb 24, 2025 at 4:12 AM Alexei Starovoitov
<alexei.starovoitov@xxxxxxxxx> wrote:
>
> 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.

OK
I will send a new version.

-- 
Regards
Yafang