[PATCH 2/3] RISC-V: build: Disable LTO for the vDSO

[Nick Desaulniers]

On Mon, Jul 19, 2021 at 1:53 PM Wende Tan <twd2.me at gmail.com> wrote:
>
> Disable LTO for the vDSO as done for x86 [1] and arm64 [2].  This also
> disables CFI for it [3].
>
> [1] https://patchwork.kernel.org/project/linux-kbuild/patch/20201009161338.657380-28-samitolvanen@google.com/
> [2] https://patchwork.kernel.org/project/kernel-hardening/patch/20201211184633.3213045-15-samitolvanen@google.com/
> [3] https://lore.kernel.org/bpf/CABCJKucpFHC-9rvT7uNF+E-Jh20fz69zdO49_4p8G_Sb634qmw@mail.gmail.com/

It might be nicer to use the typical form for commits:
commit <12 char sha> ("<oneline>")
rather than a mix of patchwork and lore links.

Do you have a list of diagnostics produced when building this object
file with LTO enabled?

>
> Signed-off-by: Wende Tan <twd2.me at gmail.com>
> ---
>  arch/riscv/kernel/vdso/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile
> index 24d936c147cd..4535a77792be 100644
> --- a/arch/riscv/kernel/vdso/Makefile
> +++ b/arch/riscv/kernel/vdso/Makefile
> @@ -30,7 +30,7 @@ obj-y += vdso.o vdso-syms.o
>  CPPFLAGS_vdso.lds += -P -C -U$(ARCH)
>
>  # Disable -pg to prevent insert call site
> -CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os
> +CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os $(CC_FLAGS_LTO)
>
>  # Disable profiling and instrumentation for VDSO code
>  GCOV_PROFILE := n
> --
> 2.25.1


-- 
Thanks,
~Nick Desaulniers