linux-kernel - Re: [PATCH v3 1/2] arch/powerpc/kvm: kvmppc_hv

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Message-ID: <ZCFoBqReJekPd7GI@li-a450e7cc-27df-11b2-a85c-b5a9ac31e8ef.ibm.com>
Date:   Mon, 27 Mar 2023 15:25:18 +0530
From:   Kautuk Consul <kconsul@...ux.vnet.ibm.com>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Fabiano Rosas <farosas@...ux.ibm.com>,
        Sathvika Vasireddy <sv@...ux.ibm.com>,
        Alexey Kardashevskiy <aik@...abs.ru>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] arch/powerpc/kvm: kvmppc_hv_entry: remove .global
 scope

On 2023-03-27 19:51:34, Nicholas Piggin wrote:
> On Mon Mar 27, 2023 at 7:34 PM AEST, Kautuk Consul wrote:
> > On 2023-03-27 14:58:03, Kautuk Consul wrote:
> > > On 2023-03-27 19:19:37, Nicholas Piggin wrote:
> > > > On Thu Mar 16, 2023 at 3:10 PM AEST, Kautuk Consul wrote:
> > > > > kvmppc_hv_entry isn't called from anywhere other than
> > > > > book3s_hv_rmhandlers.S itself. Removing .global scope for
> > > > > this function and annotating it with SYM_INNER_LABEL.
> > > > >
> > > > > Signed-off-by: Kautuk Consul <kconsul@...ux.vnet.ibm.com>
> > > > > ---
> > > > >  arch/powerpc/kvm/book3s_hv_rmhandlers.S | 3 +--
> > > > >  1 file changed, 1 insertion(+), 2 deletions(-)
> > > > >
> > > > > diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> > > > > index acf80915f406..b81ba4ee0521 100644
> > > > > --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> > > > > +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> > > > > @@ -502,8 +502,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
> > > > >   *                                                                            *
> > > > >   *****************************************************************************/
> > > > >  
> > > > > -.global kvmppc_hv_entry
> > > > 
> > > > I think this is okay.
> > > > 
> > > > > -kvmppc_hv_entry:
> > > > > +SYM_INNER_LABEL(kvmppc_hv_entry, SYM_L_LOCAL)
> > > > 
> > > > The documentation for SYM_INNER_LABEL says it for labels inside a SYM
> > > > function block, is that a problem? This is a function but doesn't have
> > > > C calling convention, so asm annotation docs say that it should use
> > > > SYM_CODE_START_LOCAL?
> > > That is correct. Will create a v4 patch for this and send it.
> > But using SYM_CODE_START_LOCAL again causes a warning in the build
> > (which we were trying to avoid):
> > arch/powerpc/kvm/book3s_hv_rmhandlers.o: warning: objtool: .text+0x48: unannotated intra-function call
> 
> Are you using SYM_FUNC_END as well? Looks like you need that to
> annotate the type properly. It should be the same as SYM_INNER_LABEL
> in the end AFAIKS.

What about SYM_CODE_START_LOCAL and SYM_CODE_END ?
This seems to work fine for me without any build warnings from objtool.
> 
> > > > 
> > > > BTW. why don't our _GLOBAL() macros use these SYM annotations? I haven't
> > > > really looked into them.
> > > Not sure. Was mostly just concentrating on the kvmppc_hv_entry code.
> 
> Looks like it's because we have a .type @function annotation in those
> already. Not sure if we should end up converting all that over to use
> the SYM annotations or if it's okay to leave it as is.
> 
> Thanks,
> Nick