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. > > 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:"
