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Date:   Mon, 21 Mar 2022 17:50:50 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Stephen Rothwell <sfr@canb.auug.org.au>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux Next Mailing List <linux-next@vger.kernel.org>,
        mhiramat@kernel.org, ast@kernel.org, hjl.tools@gmail.com,
        rick.p.edgecombe@intel.com, rppt@kernel.org,
        linux-toolchains@vger.kernel.org, Andrew.Cooper3@citrix.com,
        ndesaulniers@google.com
Subject: Re: linux-next: build warnings after merge of the tip tree
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On Mon, Mar 21, 2022 at 12:45:51PM -0400, Steven Rostedt wrote:
> On Mon, 21 Mar 2022 17:40:32 +0100
> Peter Zijlstra <peterz@infradead.org> wrote:
> 
> > func_B:
> > 	call __fentry__	/* push func_B */
> > 	...
> > 	call __fexit__	/* pop 1 + tails */
> > 	ret
> > 
> > func_A:
> > 	call __fentry__ /* push func_A */
> > 	...
> > 	call __ftail__  /* mark func_A tail */
> > 	jmp func_B
> > 
> > func_C:
> > 	call __fentry__ /* push func_C */
> > 	call func_A;
> > 	...
> > 	call __fexit__  /* pop 1 + tails */
> > 	ret;
> 
> This also assumes that we need to trace everything that is marked. I
> mentioned in another email, what do we do if we only trace funcA?

Like I said later on; if we inhibit tail-calls to notrace, this goes
away.