linux-kernel - Re: [PATCH] riscv: enable DEBUG_FORCE_FUNCTION_ALIGN

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Message-ID: <ZMZy5ZA0POhm2tAQ@xhacker>
Date:   Sun, 30 Jul 2023 22:25:41 +0800
From:   Jisheng Zhang <jszhang@...nel.org>
To:     Conor Dooley <conor@...nel.org>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org
Subject: Re: [PATCH] riscv: enable DEBUG_FORCE_FUNCTION_ALIGN_64B

On Sat, Jul 29, 2023 at 11:34:38AM +0100, Conor Dooley wrote:
> Hey,
> 
> On Fri, Jul 28, 2023 at 12:03:56AM +0800, Jisheng Zhang wrote:
> > Allow to force all function address 64B aligned as it is possible for
> > other architectures. This may be useful when verify if performance
> > bump is caused by function alignment changes.
> > 
> > Before commit 1bf18da62106 ("lib/Kconfig.debug: add ARCH dependency
> > for FUNCTION_ALIGN option"), riscv supports enabling the
> > DEBUG_FORCE_FUNCTION_ALIGN_64B option, but after that commit, each
> > arch needs to claim the support explicitly. I tried the config file in
> > [1] for both RV64 and RV32, I can't reproduce the build error as [1],
> > there is no reason for not allowing to enforce this function alignment.
> > 
> > Link: https://lore.kernel.org/lkml/202202271612.W32UJAj2-lkp@intel.com/ [1]
> 
> This is a CSKY randconfig, is there any particular reason that running
> that randconfig (over a year later) and on a different architecture
> would trigger whatever the condition was?

Just use the randconfig and then s/CSKY/RISCV to check whether RV32
and RV64 can reproduce the compile error ;)

> 
> The original commit here seems far too penal - why was it not just
> disabled on CSKY??? I tried looking a bit on lore, but didn't see
> anything explaining the subset of supported archs they picked.
> I did see Guo Ren wondering if rv32 would be similarly problematic - but
> since this is something likely to just trip up randconfigs, I think we
> should go for it and if rv32 becomes a problem, restrict this to 64-bit.
> 
> Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>
> 
> Thanks,
> Conor.
> 
> > Signed-off-by: Jisheng Zhang <jszhang@...nel.org>
> > ---
> >  lib/Kconfig.debug | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> > index fbc89baf7de6..39ffd218e960 100644
> > --- a/lib/Kconfig.debug
> > +++ b/lib/Kconfig.debug
> > @@ -502,7 +502,7 @@ config SECTION_MISMATCH_WARN_ONLY
> >  
> >  config DEBUG_FORCE_FUNCTION_ALIGN_64B
> >  	bool "Force all function address 64B aligned"
> > -	depends on EXPERT && (X86_64 || ARM64 || PPC32 || PPC64 || ARC || S390)
> > +	depends on EXPERT && (X86_64 || ARM64 || PPC32 || PPC64 || ARC || RISCV || S390)
> >  	select FUNCTION_ALIGNMENT_64B
> >  	help
> >  	  There are cases that a commit from one domain changes the function
> > -- 
> > 2.40.1
> >