linux-kernel - Re: [PATCH 2/2] powerpc/vdso32: link vdso64 with linker

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Date:   Wed, 2 Sep 2020 10:16:35 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Kees Cook <keescook@...omium.org>,
        Fangrui Song <maskray@...gle.com>
Subject: Re: [PATCH 2/2] powerpc/vdso32: link vdso64 with linker



On 9/1/20 10:25 PM, Nick Desaulniers wrote:
> Rather than invoke the compiler as the driver, use the linker. That way
> we can check --orphan-handling=warn support correctly, as cc-ldoption
> was removed in
> commit 055efab3120b ("kbuild: drop support for cc-ldoption").
> 
> Requires dropping the .got section.  I couldn't find how it was used in
> the vdso32.
> 
> Fixes: commit f2af201002a8 ("powerpc/build: vdso linker warning for orphan sections")
> Link: https://lore.kernel.org/lkml/CAKwvOdnn3wxYdJomvnveyD_njwRku3fABWT_bS92duihhywLJQ@mail.gmail.com/
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
> ---
> Not sure removing .got is a good idea or not.  Otherwise I observe the
> following link error:
> powerpc-linux-gnu-ld: warning: orphan section `.got' from `arch/powerpc/kernel/vdso32/sigtramp.o' being placed in section `.got'
> powerpc-linux-gnu-ld: _GLOBAL_OFFSET_TABLE_ not defined in linker created .got
> powerpc-linux-gnu-ld: final link failed: bad value

Finally I spotted it I think:

	make arch/powerpc/kernel/vdso32/ V=1

powerpc64-linux-ld  -EB -m elf64ppc -shared -soname linux-vdso32.so.1 
--eh-frame-hdr  --orphan-handling=warn -T 
arch/powerpc/kernel/vdso32/vdso32.lds 
arch/powerpc/kernel/vdso32/sigtramp.o 
arch/powerpc/kernel/vdso32/gettimeofday.o 
arch/powerpc/kernel/vdso32/datapage.o 
arch/powerpc/kernel/vdso32/cacheflush.o 
arch/powerpc/kernel/vdso32/note.o arch/powerpc/kernel/vdso32/getcpu.o -o 
arch/powerpc/kernel/vdso32/vdso32.so.dbg



If I do the same manually but with -m elf32ppc instead of -m elf64ppc, 
there is no failure.

Adding -m elf32ppc to ldflags-y also works, allthough I don't like too 
much having "-m elf64ppc -m elf32ppc" on the line.

Christophe