On Mon, Feb 10, 2025 at 08:12:32PM -0800, Eduard Zingerman wrote: > I'm probably out of context for this discussion, sorry if I'm raising > points already discussed. > > The DW_AT_noreturn attribute is defined for DWARF. A simple script > like [1] could be used to find all functions with this attribute known > to DWARF. Using this script I see several functions present in my > kernel but not present in the NORETURN list from this patch: > - abort > - devtmpfs_work_loop > - play_dead > - rcu_gp_kthread > - rcu_tasks_kthread > > All these are marked as FUNC symbols when doing 'readelf --symbols vmlinux'. > > 'pahole' could be modified to look for DW_AT_noreturn attributes and > add this information in BTF. E.g. by adding special btf_decl_tag to > corresponding FUNC definitions. This won't work if kernel is compiled > w/o BTF, of-course. > > [1] https://gist.github.com/eddyz87/d8513a731dfe7e2be52b346aef1de353 I also suggested this, I agree this is a much better way to go. noreturns.h is manually maintained based on objtool warnings and I'm not surprised it has missing entries. Alexei mentioned 30k+ noreturns, but when I eliminate dups and __compiletime_assert_* it's a much smaller list: $ ./noreturn_printer vmlinux |sort |uniq |grep -v compiletime_assert arch_cpu_idle_dead external idle.c arch_cpu_idle_dead external process.c cpu_startup_entry external cpu.h cpu_startup_entry external idle.c do_exit external exit.c do_exit external kernel.h do_group_exit external exit.c do_group_exit external task.h do_task_dead external core.c do_task_dead external task.h doublefault_shim external doublefault_32.c ex_handler_msr_mce external core.c ex_handler_msr_mce external extable.h __fortify_panic external fortify-string.h __fortify_panic external string_helpers.c i386_start_kernel external head32.c __ia32_sys_exit external syscalls_32.h __ia32_sys_exit_group external syscalls_32.h kthread_complete_and_exit external kthread.c kthread_exit external kthread.c kthread_exit external kthread.h machine_real_restart external reboot.c make_task_dead external exit.c __module_put_and_kthread_exit external main.c __module_put_and_kthread_exit external module.h nmi_panic_self_stop external panic.c panic external panic.c panic external panic.h panic_smp_self_stop external panic.c play_dead process.c rcu_gp_kthread tree.c rcu_tasks_kthread tasks.h rest_init main.c rewind_stack_and_make_dead external dumpstack.c start_kernel external main.c start_kernel external start_kernel.h stop_this_cpu external process.c stop_this_cpu external processor.h Also, for objtool we could use something based on your program to autogenerate noreturns.h. Only problem is, objtool doesn't currently have a dependency on CONFIG_DEBUG_INFO. Another option we've considered is compiler annotations (or compiler plugins). -- Josh
