linux-kernel - Re: [PATCH v6 4/4] risc/purgatory: Add linker script

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Date:   Fri, 5 May 2023 13:30:15 +0100
From:   Conor Dooley <conor.dooley@...rochip.com>
To:     Ricardo Ribalda <ribalda@...omium.org>
CC:     Conor Dooley <conor@...nel.org>,
        Eric Biederman <ebiederm@...ssion.com>,
        Philipp Rudo <prudo@...ux.vnet.ibm.com>,
        Dave Young <dyoung@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Tom Rix <trix@...hat.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>, Baoquan He <bhe@...hat.com>,
        Philipp Rudo <prudo@...hat.com>, <kexec@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, Ross Zwisler <zwisler@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Simon Horman <horms@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        <llvm@...ts.linux.dev>, <linuxppc-dev@...ts.ozlabs.org>,
        <linux-riscv@...ts.infradead.org>, <stable@...r.kernel.org>
Subject: Re: [PATCH v6 4/4] risc/purgatory: Add linker script

On Mon, May 01, 2023 at 09:54:43PM +0200, Ricardo Ribalda wrote:
> On Mon, 1 May 2023 at 19:41, Conor Dooley <conor@...nel.org> wrote:
> > On Mon, May 01, 2023 at 02:38:22PM +0200, Ricardo Ribalda wrote:
> > > If PGO is enabled, the purgatory ends up with multiple .text sections.
> > > This is not supported by kexec and crashes the system.
> > >
> > > Cc: stable@...r.kernel.org
> > > Fixes: 930457057abe ("kernel/kexec_file.c: split up __kexec_load_puragory")
> > > Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> > > ---
> > >  arch/riscv/purgatory/Makefile | 5 +++++
> > >  1 file changed, 5 insertions(+)
> > >
> > > diff --git a/arch/riscv/purgatory/Makefile b/arch/riscv/purgatory/Makefile
> > > index 5730797a6b40..cf3a44121a90 100644
> > > --- a/arch/riscv/purgatory/Makefile
> > > +++ b/arch/riscv/purgatory/Makefile
> > > @@ -35,6 +35,11 @@ CFLAGS_sha256.o := -D__DISABLE_EXPORTS
> > >  CFLAGS_string.o := -D__DISABLE_EXPORTS
> > >  CFLAGS_ctype.o := -D__DISABLE_EXPORTS
> > >
> > > +# When profile optimization is enabled, llvm emits two different overlapping
> > > +# text sections, which is not supported by kexec. Remove profile optimization
> > > +# flags.
> > > +KBUILD_CFLAGS := $(filter-out -fprofile-sample-use=% -fprofile-use=%,$(KBUILD_CFLAGS))
> >
> > With the caveat of not being au fait with the workings of either PGO or
> > of purgatory, how come you modify KBUILD_CFLAGS here rather than the
> > purgatory specific PURGATORY_CFLAGS that are used later in the file?
> 
> Definitely, not a Makefile expert here, but when I tried this:
> 
> @@ -35,6 +40,7 @@ PURGATORY_CFLAGS_REMOVE := -mcmodel=kernel
>  PURGATORY_CFLAGS := -mcmodel=large -ffreestanding
> -fno-zero-initialized-in-bss -g0
>  PURGATORY_CFLAGS += $(DISABLE_STACKLEAK_PLUGIN) -DDISABLE_BRANCH_PROFILING
>  PURGATORY_CFLAGS += -fno-stack-protector
> +PURGATORY_CFLAGS := $(filter-out -fprofile-sample-use=%
> -fprofile-use=%,$(KBUILD_CFLAGS))
> 
> It did not work.

Unfortunately I am oh-so-far from an expert on this kind of thing, but I
had thought that PURGATORY_CFLAGS_REMOVE was intended for this sort of
purpose.

> Fixes: bde971a83bbf ("KVM: arm64: nvhe: Fix build with profile optimization")
> 
> does this approach, so this is what I tried and worked.

That doesn't have a specific CFLAGS though afaict.
Perhaps Nick etc have a more informed opinion here than I do, sorry.

Thanks,
Conor.

> > > +
> > >  # When linking purgatory.ro with -r unresolved symbols are not checked,
> > >  # also link a purgatory.chk binary without -r to check for unresolved symbols.
> > >  PURGATORY_LDFLAGS := -e purgatory_start -z nodefaultlib
> > >
> > > --
> > > 2.40.1.495.gc816e09b53d-goog
> > >
> > >
> > > _______________________________________________
> > > linux-riscv mailing list
> > > linux-riscv@...ts.infradead.org
> > > http://lists.infradead.org/mailman/listinfo/linux-riscv
> 
> 
> 
> -- 
> Ricardo Ribalda

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