linux-kernel - Re: [RFC PATCH 4/6] arm64: clean up symbol aliasing

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Message-ID: <YbNsI31st3oXleWq@arm.com>
Date:   Fri, 10 Dec 2021 15:02:59 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     linux-kernel@...r.kernel.org, ardb@...nel.org, bp@...en8.de,
        broonie@...nel.org, dave.hansen@...ux.intel.com,
        jpoimboe@...hat.com, jslaby@...e.cz,
        linux-arm-kernel@...ts.infradead.org, maz@...nel.org,
        mingo@...hat.com, peterz@...radead.org, tabba@...gle.com,
        tglx@...utronix.de, will@...nel.org
Subject: Re: [RFC PATCH 4/6] arm64: clean up symbol aliasing

On Mon, Dec 06, 2021 at 12:47:13PM +0000, Mark Rutland wrote:
> Now that we have SYM_FUNC_ALIAS() and SYM_FUNC_ALIAS_WEAK(), use those
> to simplify and more consistently define function aliases across
> arch/arm64.
> 
> Aliases are now defined in terms of a canonical function name. For
> position-independent functions I've made the __pi_<func> name the
> canonical name, and defined other alises in terms of this.
> 
> The SYM_FUNC_{START,END}_PI(func) macros obscure the __pi_<func> name,
> and make this hard to seatch for. The SYM_FUNC_START_WEAK_PI() macro
> also obscures the fact that the __pi_<func> fymbol is global and the
> <func> symbol is weak. For clarity, I have removed these macros and used
> SYM_FUNC_{START,END}() directly with the __pi_<func> name.
> 
> For example:
> 
>     SYM_FUNC_START_WEAK_PI(func)
>         ... asm insns ...
>     SYM_FUNC_END_PI(func)
>     EXPORT_SYMBOL(func)
> 
> ... becomes:
> 
>     SYM_FUNC_START(__pi_func)
>         ... asm insns ...
>     SYM_FUNC_END(__pi_func)
> 
>     SYM_FUNC_ALIAS_WEAK(func, __pi_func)
>     EXPORT_SYMBOL(func)
> 
> For clarity, where there are multiple annotations such as
> EXPORT_SYMBOL(), I've tried to keep annotations grouped by symbol. For
> example, where a function has a name and an alias which are both
> exported, this is organised as:
> 
>     SYM_FUNC_START(func)
> 	... asm insns ...
>     SYM_FUNC_END(func)
>     EXPORT_SYMBOL(func)
> 
>     SYM_FUNC_ALAIAS(alias, func)
>     EXPORT_SYMBOL(alias)
> 
> For consistency with the other string functions, I've defined strrchr as
> a position-independent function, as it can safely be used as such even
> though we have no users today.
> 
> As we no longer use SYM_FUNC_{START,END}_ALIAS(), our local copies are
> removed. The common versions will be removed by a subsequent patch.
> 
> There should be no functional change as a result of this patch.
> 
> Signed-off-by: Mark Rutland <mark.rutland@....com>
> Cc: Ard Biesheuvel <ardb@...nel.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Mark Brown <broonie@...nel.org>
> Cc: Will Deacon <will@...nel.org>

Acked-by: Catalin Marinas <catalin.marinas@....com>