On 12/03/2020 14:20, Miroslav Benes wrote: > The unwinder reports the boot CPU idle task's stack on XEN PV as > unreliable, which affects at least live patching. There are two reasons > for this. First, the task does not follow the x86 convention that its > stack starts at the offset right below saved pt_regs. It allows the > unwinder to easily detect the end of the stack and verify it. Second, > startup_xen() function does not store the return address before jumping > to xen_start_kernel() which confuses the unwinder. > > Amend both issues by moving the starting point of initial stack in > startup_xen() and storing the return address before the jump. > > Signed-off-by: Miroslav Benes <mbenes@xxxxxxx> > --- > arch/x86/xen/xen-head.S | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S > index 1d0cee3163e4..642f346bfe02 100644 > --- a/arch/x86/xen/xen-head.S > +++ b/arch/x86/xen/xen-head.S > @@ -35,7 +35,7 @@ SYM_CODE_START(startup_xen) > rep __ASM_SIZE(stos) > > mov %_ASM_SI, xen_start_info > - mov $init_thread_union+THREAD_SIZE, %_ASM_SP > + mov $init_thread_union+THREAD_SIZE-SIZEOF_PTREGS, %_ASM_SP > > #ifdef CONFIG_X86_64 > /* Set up %gs. > @@ -51,7 +51,9 @@ SYM_CODE_START(startup_xen) > wrmsr > #endif > > + push $1f > jmp xen_start_kernel > +1: Hang on. Isn't this just a `call` instruction written in longhand? ~Andrew
