Re: [RFC] Objtool toolchain proposal: -fannotate-{jump-table,noreturn}

On Wed, Sep 14, 2022 at 01:04:16AM +0100, Josh Poimboeuf wrote:

quoted

I will mention that objtool's existence is based on mistrust, of persons 
(not correctly annotating stuff) and of tools (not correctly heeding those 
annotations).  The mistrust in persons is understandable and can be dealt 
with by tools, but the mistrust in tools can't be fixed by making tools 
more complicated by emitting even more information; there's no good reason 
to assume that one piece of info can be trusted more than other pieces.  
So, if you mistrust the tools you have already lost.  That's somewhat 
philosophical, so I won't beat that horse much more either.

Maybe this is semantics, but I wouldn't characterize objtool's existence
as being based on the mistrust of tools.  It's main motivation is to
fill in the toolchain's blind spots in asm and inline-asm, which exist
by design.

That and a fairly deep seated loathing for the regular CFI annotations
and DWARF in general. Linus was fairly firm he didn't want anything to
do with DWARF for in-kernel unwinding.

That left us in a spot that we needed unwind information in a 'better'
format than DWARF.

Objtool was born out of those contraints. ORC not needing the CFI
annotations and ORC being *much* faster at unwiding and generation
(debug builds are slow) were all good.