linux-kernel - Re: [PATCH v2 2/2] ftrace: recordmcount: Handle sections with no non-weak symbols

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Message-ID: <20220428184212.18fbf438@gandalf.local.home>
Date:   Thu, 28 Apr 2022 18:42:12 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        <linux-kernel@...r.kernel.org>, <linuxppc-dev@...ts.ozlabs.org>,
        llvm@...ts.linux.dev
Subject: Re: [PATCH v2 2/2] ftrace: recordmcount: Handle sections with no
 non-weak symbols

On Thu, 28 Apr 2022 22:49:52 +0530
"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com> wrote:

> But, with ppc64 elf abi v1 which only supports the old -pg flag, mcount
> location can differ between the weak and non-weak variants of a
> function. In such scenarios, one of the two mcount entries will be
> invalid. Such architectures need to validate mcount locations by
> ensuring that the instruction(s) at those locations are as expected. On
> powerpc, this can be a simple check to ensure that the instruction is a
> 'bl'. This check can be further tightened as necessary.

I was thinking about this more, and I was thinking that we could create
another section; Perhaps __mcount_loc_weak. And place these in that
section. That way, we could check if these symbols to see if there's
already a symbol for it, and if there is, then drop it.

-- Steve