linux-kernel - Re: [PATCH] ppc: add "-z notext" flag to disable diagnostic

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Message-ID: <87sfzde8lk.fsf@linkitivity.dja.id.au>
Date:   Sat, 14 Aug 2021 00:13:11 +1000
From:   Daniel Axtens <dja@...ens.net>
To:     Bill Wendling <morbo@...gle.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com
Cc:     Bill Wendling <morbo@...gle.com>
Subject: Re: [PATCH] ppc: add "-z notext" flag to disable diagnostic

Bill Wendling <morbo@...gle.com> writes:

> The "-z notext" flag disables reporting an error if DT_TEXTREL is set on
> PPC with CONFIG=kdump:
>
>   ld.lld: error: can't create dynamic relocation R_PPC64_ADDR64 against
>     local symbol in readonly segment; recompile object files with -fPIC
>     or pass '-Wl,-z,notext' to allow text relocations in the output
>   >>> defined in built-in.a(arch/powerpc/kernel/misc.o)
>   >>> referenced by arch/powerpc/kernel/misc.o:(.text+0x20) in archive
>       built-in.a
>
> The BFD linker disables this by default (though it's configurable in
> current versions). LLD enables this by default. So we add the flag to
> keep LLD from emitting the error.

You didn't provide a huge amount of context but I was able to reproduce
a similar set of errors with pseries_le_defconfig and

make ARCH=powerpc CROSS_COMPILE=powerpc64-linux-gnu- CC="ccache clang-11" LD=ld.lld-11 AR=llvm-ar-11 -j4 vmlinux

I also checked the manpage, and indeed the system ld does not issue this
warning/error by default.

> ---
>  arch/powerpc/Makefile | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
> index 6505d66f1193..17a9fbf9b789 100644
> --- a/arch/powerpc/Makefile
> +++ b/arch/powerpc/Makefile
> @@ -122,6 +122,7 @@ endif
>  
>  LDFLAGS_vmlinux-y := -Bstatic
>  LDFLAGS_vmlinux-$(CONFIG_RELOCATABLE) := -pie
> +LDFLAGS_vmlinux-$(CONFIG_RELOCATABLE) += -z notext

Is there any reason this should be gated on CONFIG_RELOCATABLE? (I tried
without it and got different but possibly related linker errors...)

Also, is this behaviour new?

Kind regards,
Daniel

>  LDFLAGS_vmlinux	:= $(LDFLAGS_vmlinux-y)
>  
>  ifdef CONFIG_PPC64
> -- 
> 2.33.0.rc1.237.g0d66db33f3-goog