linux-kernel - Re: [PATCH v2 2/3] memory: export symbols for memory related functions

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Message-ID: <9cb31614569fb1e121102b6bef7de8870224283c.camel@mediatek.com>
Date:   Thu, 15 Jun 2023 02:08:32 +0000
From:   Wei-chin Tsai (蔡維晉) 
        <Wei-chin.Tsai@...iatek.com>
To:     "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "angelogioacchino.delregno@...labora.com" 
        <angelogioacchino.delregno@...labora.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mel Lee (李奇錚) <Mel.Lee@...iatek.com>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        wsd_upstream <wsd_upstream@...iatek.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        Ivan Tseng (曾志軒) 
        <ivan.tseng@...iatek.com>
Subject: Re: [PATCH v2 2/3] memory: export symbols for memory related
 functions

On Wed, 2023-06-14 at 17:21 +0100, Russell King (Oracle) wrote:
>  	 
> External email : Please do not click links or open attachments until
> you have verified the sender or the content.
>  On Wed, Jun 14, 2023 at 02:11:25PM +0200, AngeloGioacchino Del Regno
> wrote:
> > Il 14/06/23 11:59, Wei-chin Tsai (蔡維晉) ha scritto:
> > > On Wed, 2023-06-14 at 08:16 +0100, Russell King (Oracle) wrote:
> > > >   
> > > > External email : Please do not click links or open attachments
> until
> > > > you have verified the sender or the content.
> > > >   On Wed, Jun 14, 2023 at 11:20:34AM +0800, Wei Chin Tsai
> wrote:
> > > > > diff --git a/arch/arm/kernel/process.c
> b/arch/arm/kernel/process.c
> > > > > index 0e8ff85890ad..df91412a1069 100644
> > > > > --- a/arch/arm/kernel/process.c
> > > > > +++ b/arch/arm/kernel/process.c
> > > > > @@ -343,6 +343,7 @@ const char *arch_vma_name(struct
> vm_area_struct
> > > > *vma)
> > > > >   {
> > > > >   return is_gate_vma(vma) ? "[vectors]" : NULL;
> > > > >   }
> > > > > +EXPORT_SYMBOL_GPL(arch_vma_name);
> > > > ...
> > > > > diff --git a/kernel/signal.c b/kernel/signal.c
> > > > > index b5370fe5c198..a1abe77fcdc3 100644
> > > > > --- a/kernel/signal.c
> > > > > +++ b/kernel/signal.c
> > > > > @@ -4700,6 +4700,7 @@ __weak const char *arch_vma_name(struct
> > > > vm_area_struct *vma)
> > > > >   {
> > > > >   return NULL;
> > > > >   }
> > > > > +EXPORT_SYMBOL_GPL(arch_vma_name);
> > > > 
> > > > Have you confirmed:
> > > > 1) whether this actually builds
> > > > 2) whether this results in one or two arch_vma_name exports
> > > > 
> > > > ?
> > > > 
> > > > -- 
> > > > RMK's Patch system: 
> https://www.armlinux.org.uk/developer/patches/
> > > > FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at
> last!
> > > 
> > > Hi Russell,
> > > 
> > > We did confirm that it can be built successfully in kernel 6.1
> and run
> > > well in our system.
> > > 
> > 
> > It runs well in your system and can be built successfully because
> you're building
> > for ARM64, not for ARM...
> > 
> > > Actually, we only use this export symbol "arch_vma_name"
> > > from kernel/signal.c in arm64. We also export symbol for
> arch_vma_name
> > > in arch/arm/kernel/process.c because that, one day in the
> future,  we
> > > are afraid that we also need this function in arm platform.
> 
> What I'm trying to get at is that we have arch_vma_name in
> arch/arm/kernel/process.c and also a weak function in
> kernel/signal.c.
> 
> Both of these end up adding an entry into the __ksymtab_strings
> section and a ___ksymtab section for this symbol. So we end up with
> two entries in each.
> 
> Now, if the one from kernel/signal.c points at its own weak function,
> and that is found first, then that's the function that is going to be
> bound, not the function that's overriding it.
> 
> If, instead, the export in kernel/signal.c ends up pointing at the
> overriden function, then the export in arch/arm/kernel/process.c is
> entirely redundant.
> 
> So, you need to get to the bottom of this... and until you do I'm
> afraid I'll have to NAK this patch.
> 
> For the record, I suspect it's the latter scenario (we end up with
> two entries pointing at the same function) but that's nothing more
> than a hunch.
> 
> -- 
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/

Hi Russell,

OK, I will do the research for your questions...

Thanks.


> FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!