Re: [tip: objtool/core] objtool: Add CONFIG_OBJTOOL_WERROR

[Steven Rostedt]

On Mon, 17 Mar 2025 17:05:22 -0700
Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote:


> Hm, I'm actually surprised randconfig doesn't set COMPILE_TEST.
> 
> Anyway, the warnings are valid:
> 
>   vmlinux.o: error: objtool: do_syscall_64+0x40: call to ftrace_likely_update() leaves .noinstr.text section
>   vmlinux.o: error: objtool: do_int80_emulation+0x30: call to ftrace_likely_update() leaves .noinstr.text section
>   vmlinux.o: error: objtool: do_fast_syscall_32+0x7b: call to ftrace_likely_update() leaves .noinstr.text section
>   ...
> 
> Those are triggered by CONFIG_TRACE_BRANCH_PROFILING which adds a
> function call to ftrace_likely_update() for every likely() / unlikely().
> Which obliterates the noinstr rules.
> 
> Steven, do you still want to keep that config option?

Yes, in fact I just ran it a couple of months ago:

  https://rostedt.org/branches/current/

That's the output of both the likely and unlikely output as well as the
full branch tracer. I do look at this to fix places that are incorrect.

> 
> If so, I suppose we could make OBJTOOL_WERROR depend on
> !TRACE_BRANCH_PROFILING.
> 

That, or you can disable it for files with:

  CFLAGS_<file>.o += -DDISABLE_BRANCH_PROFILING

In the Makefile.

-- Steve