Re: [PATCH v5 07/10] x86/asm/acpi: Fix asmvalidate warnings for wakeup_64.S

Josh Poimboeuf
2015-06-10T14:08:50Z

On Wed, Jun 10, 2015 at 03:19:14PM +0200, Pavel Machek wrote:
> Hi!
>
> > Fix the following asmvalidate warnings:
> >
> > asmvalidate: arch/x86/kernel/acpi/wakeup_64.o: wakeup_long64()+0x15: unsupported jump to outside of function
> > asmvalidate: arch/x86/kernel/acpi/wakeup_64.o: wakeup_long64()+0x55: unsupported jump to outside of function
> > asmvalidate: arch/x86/kernel/acpi/wakeup_64.o: wakeup_long64(): unsupported fallthrough at end of function
> > asmvalidate: arch/x86/kernel/acpi/wakeup_64.o: do_suspend_lowlevel()+0x9a: unsupported jump to outside of function
> > asmvalidate: arch/x86/kernel/acpi/wakeup_64.o: do_suspend_lowlevel()+0x116: unsupported jump to outside of function
> > asmvalidate: arch/x86/kernel/acpi/wakeup_64.o: do_suspend_lowlevel(): unsupported fallthrough at end of function
> > asmvalidate: arch/x86/kernel/acpi/wakeup_64.o: do_suspend_lowlevel(): missing FP_SAVE/RESTORE macros
> >
> > 1. wakeup_long64() isn't a function that can be called. It's actually
> > redirected to via a return instruction in the entry code. It
> > shouldn't be annotated as a callable function. Change ENDPROC ->
> > PROC accordingly.
>
> But I see -> END.

Oops! It should say -> END.

> > 2. do_suspend_lowlevel() is a non-leaf callable function, so
> > save/restore the frame pointer with FP_SAVE/RESTORE.
>
> It does not work with the frame pointer itself. Is FP_SAVE/RESTORE
> still neccessary? Will you need FP_RESTORE to wakeup_long64, then?

wakeup_long64 jumps to .Lresume_point, which does the FP_RESTORE.

> > 3. Remove the unnecessary jump to .Lresume_point, as it just results in
> > jumping to the next instruction (which is a nop because of the
> > align). Otherwise asmvalidate gets confused by the jump.
>
> It also results in flushing the pipeline. Ok, I guess this one is unneccessary.
>
> > 4. Change the "jmp restore_processor_state" to a call instruction,
> > because jumping outside the function's boundaries isn't allowed. Now
> > restore_processor_state() will return back to do_suspend_lowlevel()
> > instead of do_suspend_lowlevel()'s caller.
> >
> > 5. Remove superfluous rsp changes.
>
> Did you test the changes?

Yes, I verified that it didn't break suspend/resume on my system.

> Do you plan to make similar changes to wakeup_32.S?

Currently, asmvalidate is x86_64 only, so I'm only fixing the 64-bit
stuff right now.

> > diff --git a/arch/x86/kernel/acpi/wakeup_64.S b/arch/x86/kernel/acpi/wakeup_64.S
> > index 8c35df4..7e442be 100644
> > --- a/arch/x86/kernel/acpi/wakeup_64.S
> > +++ b/arch/x86/kernel/acpi/wakeup_64.S
> > @@ -5,6 +5,7 @@
> > #include <asm/page_types.h>
> > #include <asm/msr.h>
> > #include <asm/asm-offsets.h>
> > +#include <asm/func.h>
> >
> > # Copyright 2003 Pavel Machek <pavel@suse.cz>, distribute under GPLv2
> >
> > @@ -33,13 +34,13 @@ ENTRY(wakeup_long64)
> >
> > movq saved_rip, %rax
> > jmp *%rax
> > -ENDPROC(wakeup_long64)
> > +END(wakeup_long64)
> >
>
> This should result in no binary code changes, so that's ok with me...
>
> > ENTRY(do_suspend_lowlevel)
> > - subq $8, %rsp
> > + FP_SAVE
> > xorl %eax, %eax
> > call save_processor_state
> >
>
> Are you sure? Stuff like
> movq $saved_context, %rax
> movq %rsp, pt_regs_sp(%rax)
>
> follows. And you did not modify wakeup_long64, which now receives
> different value in saved_rsp.

Hm, I'm looking hard, but I still don't see a problem with that code.
It's saving rsp to the saved_context struct. As I mentioned above, it's
ok for the wakeup_long64 path to restore the same rsp value, since it
jumps to .Lresume_point which has FP_RESTORE.

> > @@ -108,8 +108,9 @@ ENTRY(do_suspend_lowlevel)
> > movq pt_regs_r15(%rax), %r15
> >
> > xorl %eax, %eax
> > - addq $8, %rsp
> > - jmp restore_processor_state
> > + call restore_processor_state
> > + FP_RESTORE
> > + ret
> > ENDPROC(do_suspend_lowlevel)
>
> Umm. I rather liked the direct jump.

Why?

--
Josh