From: Rafael Ávila de Espíndola rafael@espindo.la
[ 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 b854ebf5851b..2384a2ae5ec3 100644 --- a/arch/x86/kernel/vmlinux.lds.S +++ b/arch/x86/kernel/vmlinux.lds.S @@ -390,7 +390,7 @@ 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);