netdev - Re: [PATCH net-next v4] net: skb: prevent the split of kfree_skb

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Date:   Fri, 19 Aug 2022 00:31:44 +0800
From:   Menglong Dong <menglong8.dong@...il.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     kuba@...nel.org, miguel.ojeda.sandonis@...il.com, ojeda@...nel.org,
        davem@...emloft.net, edumazet@...gle.com, pabeni@...hat.com,
        asml.silence@...il.com, imagedong@...cent.com,
        luiz.von.dentz@...el.com, vasily.averin@...ux.dev,
        jk@...econstruct.com.au, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, kernel test robot <lkp@...el.com>,
        linux-toolchains <linux-toolchains@...r.kernel.org>
Subject: Re: [PATCH net-next v4] net: skb: prevent the split of
 kfree_skb_reason() by gcc

Hello,
On Wed, Aug 17, 2022 at 11:54 PM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> On Mon, Aug 15, 2022 at 8:29 PM <menglong8.dong@...il.com> wrote:
> >
> > From: Menglong Dong <imagedong@...cent.com>
> >
> > Sometimes, gcc will optimize the function by spliting it to two or
> > more functions. In this case, kfree_skb_reason() is splited to
> > kfree_skb_reason and kfree_skb_reason.part.0. However, the
> > function/tracepoint trace_kfree_skb() in it needs the return address
> > of kfree_skb_reason().
>
> Does the existing __noclone function attribute help at all here?
>
> If not, surely there's an attribute that's more precise than "disable
> most optimization outright."
>
> https://unix.stackexchange.com/questions/223013/function-symbol-gets-part-suffix-after-compilation
> https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noclone-function-attribute
>
> Perhaps noipa might also work here?
>

In my testing, both 'noclone' and 'noipa' both work! As for the
'-fdisable-ipa-fnsplit', it seems it's not supported by gcc, and I
failed to find any documentation of it.

I think that the '__noclone' is exactly what I needed! Just like what
saied in this link:

https://stackoverflow.com/questions/34086769/purpose-of-function-attribute-noclone

I appreciate your advice, and it seems it's not needed to
add new attributes to the compiler_attributes.h.

Thanks!
Menglong Dong