On Wed, Dec 19, 2018 at 11:02 AM <ndesaulni...@google.com> wrote: > > From: Rafael Ávila de Espíndola <raf...@espindo.la> > > The kernel has many variables that it wants to have per CPU. It is > similar to how each thread wants a copy of a thread local variable. > > To access such variable, the code has to find the offset of that > variable in the per cpu block and add it to the address of the current > brock for that cpu. > > 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 ld.lld does not implement this behavior. Instead, we can > explicitly mark non-absolute terms ABSOLUTE via linker script. This is > no functional change for ld.bfd which coverts the term to ABSOLUTE > anyways as specified above. > > Reported-by: Dmitry Golovin <d...@golovin.in> > Tested-by: Dmitry Golovin <d...@golovin.in> > Suggested-by: Borislav Petkov <b...@alien8.de> > Suggested-by: Michael Matz <m...@suse.de> > Signed-off-by: Tri Vo <tr...@android.com> > Signed-off-by: Nick Desaulniers <ndesaulni...@google.com> > Signed-off-by: Rafael Ávila de Espíndola <raf...@espindo.la> > [nd: commit message updated as per Boris' and Michael's sugguestions]
Happy new year. Bumping for review. > --- > Changes from v1 -> v2: commit message updated > > 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); > > -- > 2.20.1.415.g653613c723-goog > -- Thanks, ~Nick Desaulniers
