On Tue, Jul 9, 2019 at 11:39 AM Alexey Dobriyan <adobri...@gmail.com> wrote: > > On Mon, Jul 08, 2019 at 12:35:13PM -0700, Thomas Garnier wrote: > > On Mon, Jul 8, 2019 at 12:09 PM Alexey Dobriyan <adobri...@gmail.com> wrote: > > > > > > Thomas Garnier wrote: > > > > - "pushq $1f\n\t" > > > > + "movabsq $1f, %q0\n\t" > > > > + "pushq %q0\n\t" > > > > "iretq\n\t" > > > > UNWIND_HINT_RESTORE > > > > "1:" > > > > > > Fake PIE. True PIE looks like this: > > > > I used movabsq in couple assembly changes where the memory context is > > unclear and relative reference might lead to issues. It happened on > > early boot and hibernation save/restore paths. Do you think a relative > > reference in this function will always be accurate? > > As long as iretq target is not too far it should be OK. > > I'm not really sure which issues can pop up. > > IRETQ is 64-bit only, RIP-relative addressing is 64-bit only. > Assembler (hopefully) will error compilation if target is too far. > > And it is shorter than movabsq.
Agree, I will change it and run some tests for the next iteration. > > > > ffffffff81022d70 <do_sync_core>: > > > ffffffff81022d70: 8c d0 mov eax,ss > > > ffffffff81022d72: 50 push rax > > > ffffffff81022d73: 54 push rsp > > > ffffffff81022d74: 48 83 04 24 08 add QWORD PTR [rsp],0x8 > > > ffffffff81022d79: 9c pushf > > > ffffffff81022d7a: 8c c8 mov eax,cs > > > ffffffff81022d7c: 50 push rax > > > ffffffff81022d7d: ===> 48 8d 05 03 00 00 00 lea rax,[rip+0x3] > > > # ffffffff81022d87 <do_sync_core+0x17> > > > ffffffff81022d84: 50 push rax > > > ffffffff81022d85: 48 cf iretq > > > ffffffff81022d87: c3 ret > > > > > > Signed-off-by: Alexey Dobriyan <adobri...@gmail.com> > > > > > > --- a/arch/x86/include/asm/processor.h > > > +++ b/arch/x86/include/asm/processor.h > > > @@ -710,7 +710,8 @@ static inline void sync_core(void) > > > "pushfq\n\t" > > > "mov %%cs, %0\n\t" > > > "pushq %q0\n\t" > > > - "pushq $1f\n\t" > > > + "leaq 1f(%%rip), %q0\n\t" > > > + "pushq %q0\n\t" > > > "iretq\n\t" > > > UNWIND_HINT_RESTORE > > > "1:"
