Messages in this thread | | | From | Nick Desaulniers <> | Date | Wed, 5 Dec 2018 10:21:51 -0800 | Subject | Re: [PATCH 2/2] ARM: Wrap '--pic-veneer' with ld-option |
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On Wed, Dec 5, 2018 at 12:10 AM Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote: > > (+ Arnd) > > On Wed, 5 Dec 2018 at 09:06, Nathan Chancellor <natechancellor@gmail.com> wrote: > > > > On Wed, Dec 05, 2018 at 08:37:05AM +0100, Ard Biesheuvel wrote: > > > On Wed, 5 Dec 2018 at 02:42, Nathan Chancellor <natechancellor@gmail.com> wrote: > > > > > > > > This flag is not supported by lld: > > > > > > > > ld.lld: error: unknown argument: --pic-veneer > > > > > > > > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> > > > > > > Hi Nate, > > > > > > Does this mean ld.lld is guaranteed to produce position independent > > > veneers if you build kernels that are bigger than the typical range of > > > a relative branch?
(+ Peter) who might be able to answer this.
> > > > > > > Hi Ard, > > > > Honestly, I'm not quite sure. I saw your commit that introduced this > > flag and I wasn't quite sure what to make of it for lld. What > > configuration would I use to verify and what would I check for? > > > > Try building allyesconfig, and check the resulting binary for veneers > (which have 'veneer' in the symbol name, at least when ld.bfd emits > them). These veneers should not take the [virtual] address of the > branch target directly, but take a PC relative offset (as in the > example in the commit log of that patch you are referring to)
Not sure clang can compile an arm32 allyesconfig (haven't tried personally, yet, TODO), but we could try gcc+lld.
> > > Additionally, I have filed an LLVM bug for the lld developers to > > check and see if this is a flag they should support: > > > > https://bugs.llvm.org/show_bug.cgi?id=39886 > > > > Thanks for the quick reply, > > Nathan > > > > > > --- > > > > arch/arm/Makefile | 2 +- > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > diff --git a/arch/arm/Makefile b/arch/arm/Makefile > > > > index e2a0baf36766..4fab2aa29570 100644 > > > > --- a/arch/arm/Makefile > > > > +++ b/arch/arm/Makefile > > > > @@ -10,7 +10,7 @@ > > > > # > > > > # Copyright (C) 1995-2001 by Russell King > > > > > > > > -LDFLAGS_vmlinux := --no-undefined -X --pic-veneer > > > > +LDFLAGS_vmlinux := --no-undefined -X $(call ld-option,--pic-veneer) > > > > ifeq ($(CONFIG_CPU_ENDIAN_BE8),y) > > > > LDFLAGS_vmlinux += --be8 > > > > KBUILD_LDFLAGS_MODULE += --be8 > > > > -- > > > > 2.20.0.rc1 > > > >
-- Thanks, ~Nick Desaulniers
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