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    Subject[PATCH 5.0 231/246] x86/build: Mark per-CPU symbols as absolute explicitly for LLD
    Date
    5.0-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    [ Upstream commit d071ae09a4a1414c1433d5ae9908959a7325b0ad ]

    Accessing per-CPU variables is done by finding the offset of the
    variable in the per-CPU block and adding it to the address of the
    respective CPU's block.

    Section 3.10.8 of ld.bfd's documentation states:

    For expressions involving numbers, relative addresses and absolute
    addresses, ld follows these rules to evaluate terms:

    Other binary operations, that is, between two relative addresses
    not in the same section, or between a relative address and an
    absolute address, first convert any non-absolute term to an
    absolute address before applying the operator."

    Note that LLVM's linker does not adhere to the GNU ld's implementation
    and as such requires implicitly-absolute terms to be explicitly marked
    as absolute in the linker script. If not, it fails currently with:

    ld.lld: error: ./arch/x86/kernel/vmlinux.lds:153: at least one side of the expression must be absolute
    ld.lld: error: ./arch/x86/kernel/vmlinux.lds:154: at least one side of the expression must be absolute
    Makefile:1040: recipe for target 'vmlinux' failed

    This is not a functional change for ld.bfd which converts the term to an
    absolute symbol anyways as specified above.

    Based on a previous submission by Tri Vo <trong@android.com>.

    Reported-by: Dmitry Golovin <dima@golovin.in>
    Signed-off-by: Rafael Ávila de Espíndola <rafael@espindo.la>
    [ Update commit message per Boris' and Michael's suggestions. ]
    Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
    [ Massage commit message more, fix typos. ]
    Signed-off-by: Borislav Petkov <bp@suse.de>
    Tested-by: Dmitry Golovin <dima@golovin.in>
    Cc: "H. Peter Anvin" <hpa@zytor.com>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Brijesh Singh <brijesh.singh@amd.com>
    Cc: Cao Jin <caoj.fnst@cn.fujitsu.com>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: Joerg Roedel <jroedel@suse.de>
    Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
    Cc: Masami Hiramatsu <mhiramat@kernel.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Tri Vo <trong@android.com>
    Cc: dima@golovin.in
    Cc: morbo@google.com
    Cc: x86-ml <x86@kernel.org>
    Link: https://lkml.kernel.org/r/20181219190145.252035-1-ndesaulniers@google.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/x86/kernel/vmlinux.lds.S | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
    index 0d618ee634ac..ee3b5c7d662e 100644
    --- a/arch/x86/kernel/vmlinux.lds.S
    +++ b/arch/x86/kernel/vmlinux.lds.S
    @@ -401,7 +401,7 @@ SECTIONS
    * Per-cpu symbols which need to be offset from __per_cpu_load
    * for the boot processor.
    */
    -#define INIT_PER_CPU(x) init_per_cpu__##x = x + __per_cpu_load
    +#define INIT_PER_CPU(x) init_per_cpu__##x = ABSOLUTE(x) + __per_cpu_load
    INIT_PER_CPU(gdt_page);
    INIT_PER_CPU(irq_stack_union);

    --
    2.19.1


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