[PATCH AUTOSEL 3.18 39/41] x86/build: Mark per-CPU symbols as absolute explicitly for LLD

[Sasha Levin]

From: Rafael Ãvila de EspÃndola <rafael@xxxxxxxxxx>

[ 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@xxxxxxxxxxx>.

Reported-by: Dmitry Golovin <dima@xxxxxxxxxx>
Signed-off-by: Rafael Ãvila de EspÃndola <rafael@xxxxxxxxxx>
[ Update commit message per Boris' and Michael's suggestions. ]
Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
[ Massage commit message more, fix typos. ]
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Tested-by: Dmitry Golovin <dima@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Brijesh Singh <brijesh.singh@xxxxxxx>
Cc: Cao Jin <caoj.fnst@xxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Joerg Roedel <jroedel@xxxxxxx>
Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Tri Vo <trong@xxxxxxxxxxx>
Cc: dima@xxxxxxxxxx
Cc: morbo@xxxxxxxxxx
Cc: x86-ml <x86@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20181219190145.252035-1-ndesaulniers@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 49edf2dd3613..1bd47a144db1 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -345,7 +345,7 @@ 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