linux-kernel - Re: [RFC PATCH v2 11/20] objtool: Flesh out warning related to pv

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Message-ID: <20230801160636.ko3oc4cwycwejyxy@treble>
Date:   Tue, 1 Aug 2023 11:06:36 -0500
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Valentin Schneider <vschneid@...hat.com>,
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Subject: Re: [RFC PATCH v2 11/20] objtool: Flesh out warning related to
 pv_ops[] calls

On Mon, Jul 31, 2023 at 11:46:12PM +0200, Peter Zijlstra wrote:
> > Ideally it would only print a single warning for this case, something
> > like:
> > 
> >   vmlinux.o: warning: objtool: __flush_tlb_all_noinstr+0x4: indirect call to native_flush_tlb_local() leaves .noinstr.text section
> 
> But then what for the case where there are multiple implementations and
> more than one isn't noinstr?

The warning would be in the loop in pv_call_dest(), so it would
potentially print multiple warnings, one for each potential dest.

> IIRC that is where these double prints came from. One is the callsite
> (always one) and the second is the offending implementation (but there
> could be more).

It's confusing to warn about the call site and the destination in two
separate warnings.  That's why I'm proposing combining them into a
single warning (which still could end up as multiple warnings if there
are multiple affected dests).

> > I left out "pv_ops[1]" because it's already long enough :-)
> 
> The index number is useful when also looking at the assembler, which
> IIRC is an indexed indirect call.

Ok, so something like so?

  vmlinux.o: warning: objtool: __flush_tlb_all_noinstr+0x4: indirect call to pv_ops[1] (native_flush_tlb_local) leaves .noinstr.text section

-- 
Josh